You should replace the TPS and tell us if that works 'cause ive done about the same things you've done and still have a similar problem... I just haven't replaced the TPS (I cleaned the IAP, it was pretty dirty and fixed the problem *slightly*)

So, if you buy a new one and it works I can confidently do the same

Alright, I just bought a TPS and an IAC. It's dark, so I can't put them on now, but I'm going to do it first thing tomorrow morning. Everyone sacrifice a Honda to the Fiero gods for me, I need their favor!

Okay, all of you who said TPS or IAC, go to your rooms.

No effect whatsoever. The lumpy idle, the misfiring at idle, it's all still there.

Guess I should have kept that car and had Ed Parks put in a 4.9--that would fix that idle problem. Sorry again to hear it is giving you fits.

Jeff

damn, I knew it would'nt be that easy. I'm still following ya.

Whoops... I misread one of your posts.. Sounds like you're having a lean condition. I don't believe it is electrical then, because otherwise you would be experiencing a rich condition at the exhaust. I think I read that you replaced the fuel pump earlier, and the fuel filter. When you smell your exhaust, does it smell like gasoline/rich? I suppose it could be possible that you have an exhaust leak before your O2, causing false readings, and the ECM adjusting it the other way, but that would most likely only happen *after* it's warmed up. I don't think it would explain it while it's cold. Gasket leak would also cause this all the time - I don't remember you saying if you checked the intake or not... I don't know the 2.5 too well, but I think you need to check the entire intake tract for leaks with carb cleaner or a length of hose for a stethoscope. And you did buy used TPS/IAC right?

wait a sec... how many miles? - it could very well be that noisy timing gear

[This message has been edited by ryan.hess (edited 12-16-2003).]

Jeff, that 4.9 might still be the ultimate solution for this car. It's really a great car, runs excellent except for at idle.

Ryan, don't tell me "whoops" after I spend $100 on a NEW TPS and a NEW IAC!
That's okay, it may be me wanting to feel a difference, but I think it smoothed out the car's throttle response a bit. I don't have any more stuttering at 3k rpms.

I have yet to test or replace the fuel pump, that's next on my list. I'm going to perform the diagnostic tests in the service manual (one for flow, one for pressure), and that should give me a good idea as to whether the problem is fuel delivery related. I haven't noticed a strong gasoline smell from the exhaust, but I try to inhale as little exhaust as possible.

I hadn't thought of an exhaust leak. The car doesn't have a cat (straight pipe), but that's after the O2. I wonder if that could still cause problems. I'll definitely check both the exhaust and intake for cracks/leaks.

Oh, and to clarify, the bad idle occurs after the car has warmed up fully, not just at startup. The car does the normal Fiero idle high, then gradually come down thing when you first start it, but I haven't had a Fiero that didn't do that.

The car has a little over 110k miles on it, and those gears are a little annoying. They make the car sound like it's a diesel.

Today, just to feel like I'm making progress, I replaced the TBI base gasket. No change, but it needed replacement anyway.

[This message has been edited by HummelHund (edited 12-16-2003).]

quote Originally posted by HummelHund: Ryan, don't tell me "whoops" after I spend $100 on a NEW TPS and a NEW IAC! That's okay, it may be me wanting to feel a difference, but I think it smoothed out the car's throttle response a bit. I don't have any more stuttering at 3k rpms.

I believe I said swap it for a used one I'm not sure if not having a cat would do much, maybe someone else knows. So why can't the timing be set on your 2.5? (not familiar)

[This message has been edited by ryan.hess (edited 12-17-2003).]

The Distributorless Ignition System (DIS) found on 87-88' 2.5's controls the timing, so it is non-adjustable.

It's been awhile...and I've done nothing to the car. Still having the problems, I just haven't had the time to take a look at it. But, now I'll be driving around 200 miles a week in the Fiero, so it's going to get some well deserved preventative maintenence...

1. Clutch Master & Slave Cylinders, and bleeding- The clutch still works great, but pedal pressure is low and the master has been leaking for some time now. Time to finally break down and replace them...

2. Brake Hoses- Finishing up a job from a few months ago, I'm putting Earl's stainless steel brake hoses on the rear. I only had time for the fronts when I started the job.

3. Cooling System Overhaul- All new hoses, caps, t-stat, and a flush and fill. I recently replaced the heater core, so that's one less thing to replace.

4. Timing Gears- This is the big one, it may have to wait until spring break, when I have some time to get to it. It's a tough job, but I don't have the cash to take it somewhere, and I feel confident that, with a little help from my friends and family, I can get the job done.

5. Finally, a Rodney Dickman OEM style Cat-Con to replace the straight pipe that's on the car now. It makes the car sound like a large, gassy bee, so this will be a definite improvement.

From there, who knows? A paint job! Mr. Mike's Seats! Some of them spinnin' 20" wheels and a set a' neons fer tha bling-bling factor! A Huly-Huly girl to go on the dash! The possibilities are endless!

It'll still miss at idle, though...

It saddens me to hear this man.......I have the same problem (along with everybody else) Well one thing I would suggest.....and I heard this somewhere, is get your ignition module, and clean the base of the module off, and the base of the dist. off really really really really really good. Then apply a brand spankin new coat of dielectric grease on there and see what that does. Somebody told me that it needs to be clean because the dist. base is where the module uses as a ground. And also, the thing that somebody said before about $Rich$ adding a ground. He added a ground to the EGR valve on his V6 and it helped out a whole lot he said. I would just add redundant stupid grounds everywhere and see what that does. I mean it can't hurt can it?

Austin

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Practice makes perfect, but since nobody's perfect, why practice?
If life gives you lemons, take them and throw them at people you hate.

Thanks for the suggestion, but this is an 88', with the DIS motor, so there is no ignition module or distributor. I will try to clean up the DIS brick and see if that does anything. Since my last post, I've replaced the brake booster vacuum hoses, with no effect, and tested the fuel pressure, which tested good at 11.5PSI at engine off/ignition on and 13PSI at idle. Next step, when I get the brakes fixed, is to get the alternator and battery tested. One step at a time...

While I'm thinking of it, you should probably replace the battery cables (positive and negative). It'll only cost you.....$10 maybe (only a dent in what you've already thrown at this thing). I'm sorry if this has been repeated or anything, but have you checked your timing gear? Or the voltage to your fuel pump? Have you put any of that.......well the only product that I know of is SeaFoam, but you dump it in your crankcase when you change your oil....tried that? BTW, what gasket were you talking about with the TBI? Was it the TBI and the air filter assembly or the TBI and intake gasket? I'm only a beginning mechanic but I'm just trying to think of anything that could cause you some grief. Also, I were again suggest for putting more grounds on the car. It can't hurt.

Austin

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Practice makes perfect, but since nobody's perfect, why practice?
If life gives you lemons, take them and throw them at people you hate.

HummelHund,
Don't know if your idle is still unresolved. I've been beating my head against a wall for a couple of years on a very similar problem. Solved it tonight. Check the gasket between the upper and lower throttle body castings. This gasket can be installed backwards/upsidedown. This will not allow the IAC to function in that the air passage is blocked. My car ran fine for two years outside of a lousy idle with this gasket snafu. I bought the car with this known idle problem and went through many of the same troubleshooting efforts you seem to have done.

Bump

If anyone can shed some new light, please do. My Fiero still idles poorly, and now smokes on occasion. Here's the scenario: Pull up to a stoplight, the car begins to idle roughly, bouncing between 700-1100rpm, stuttering, some smoke and it smells like it's running rich. After doing that for a minute or so, it'll rev up by itself to around 1200rpm, the SES light comes on, and it idles perfectly at 900rpm.

So what's the deal?

What code is it throwing @ u? my car hiccups just before throwing a rich code, then throws the idle up to 1000 (usuall idles 800-900)

[This message has been edited by JamesCurtis (edited 07-26-2004).]

I haven't pulled the codes in a while, but I seem to remember it was giving me a Lean Idle Code, which was strange. If I have some time tomorrow, I'll get the ol' Fiero to cough up the codes again.

HummelHund,

Just a word of encouragement for you.
I have been watching this thread and been dealing with the same thing with my 87GT. The confounded thing is the while the 87 has the hunting idle, my 86 has a rock steady idle. I know that you have a 4 cylinder and I have a 6 cylinder but the principals are the same.

Pretty much the same thing here, very good grounds, CS alternator, fresh heads on up, good tune up parts, no codes, no vacuum leaks, fresh injectors, fresh filters and a rebuilt distributor from the Fiero store. I have switched out a couple of parts from the 86 such as the TPS and coil and still have not nailed this down yet.

Am I wrong to think that the difficulties are related to just the ECM, IAC, O2 sensor and maybe the MAT sensor in the air cleaner. Now here is what I am thinking. The hunting idle is overshooting to both the high rpm and the low rpm which makes me think that one or more of the 4 components is too slow in sending a signal or reacting to a signal. ( I hope that I conveyed that concept properly.) Lets forget about the TPS right now because it isn't doing anything as you are sitting at a light with a hunting idle.

My thought is that perhaps there is a difference in the quality of the replacement parts?
Are some brands faster than others?
Is there an updated PROM for the ECM that is processing information faster?
We have some very smart folks here at PFF, maybe we can get some more input on this?
What do you think about this?
I would be more than willing to try this idea out if I could get the recomendations on the brands the perform the best and share the info I get with you.
tm

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jetman
Silver 86 SE 2M6 4-speed, with "check wallet light" and "a good nights sleep"

jetman- Thanks for the reply. I really do think some real investigation into this sort of problem would help a lot of Fiero owners who are in the same boat we're in.

As far as replacement parts are concerned, I tried to stay with AC Delco if possible (especially the EGR) and Borg Warner if not. I think the O2 sensor was a Bosch. I've had some problems with Wells parts in the past, and they really just feel cheap to me, so I stayed away from them.

There is an updated PROM, and I haven't tried that yet. I don't think that's the root of the problem, though, since many Fieros are running and not exhibiting the symptoms mine is. Ed Parks was kind enough to send me a full computer to try out, and it didn't change anything. I keep thinking it must be something extremely simple that I'm just overlooking.

Sean
I don't know if this would have any effect or not but it might be worth checking. When I pulled the TBI off of my old duke to put on the new one I got from you, the EGR passage under the gasket was solid carbon. Rock hard. Totally blocked end-to-end. So effectivily my EGR was blocked off. Have you looked at yours. A new TBI gasket is not real expensive and yours probably needs replacing too. Add that it might be compressed and heat soaked so a slight vaccum leak is also possible. Not a hard thing to change and could bring lots of results. BTW, underneath the TBI my IAC passages were pretty gummed up too. Another area that could help things out. Good luck.

I hope to fire that engine up for the first time this weekend. It has been a long road!

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Dwayne,

Great to hear the engine's almost ready to go!

I've done the whole decarbonization thing using a kit from Ed Parks, and it seemed to clean out most of the crud in the intake system .When I had the EGR off to replace it, there were some carbon deposits, but definitely not so much as to clog up any ports. It's been a few months, though, so when I get some time I may take it all apart again to double check it.

I also have already replaced the TBI gasket, as well as the TBI, so I'm pretty sure that's not the problem.

Thanks for the help!

86 SE (V6) 101,000 miles

Bought the car with only 79,000 about 3.5 years ago. When I bought the car, it sounded the same as it does now, like it has some kind of exhast leak and you can hear the insides of the engine a little more than normal. But when I bought the car, it would start up instantly, almost likely you didn't even have to turn the key. Super fast starting and it had a perfect idle and everything. That lasted about 1.5 years, and now it takes about 0.5 to 1.0 sec to start, so now it feels like all the other cars I have ever owned. And now it also idles a little rough and the rpms bouce a little between 400 and 1100 when cold, so if I don't try smoothing the rpms with the gas petal, it will sometimes stall because of the boucing idle when cold. So I think I am in the right thread of this forum. So I don't think my issue is related to the TBI gasket, since I haven't touched that and it ran perfect for 1.5years after buying the car. Fuel filter, all filters, O2 sensor, spark plugs, ignition module, cap, etc, have been replaced. But no difference. New alternator, no difference. SeaFoam is in the crankcase right now and will be chaning the oil tomorrow, but since I still don't feel a difference, I don't think SeaFoam helped that. Checked the codes, and I know it said "Lean Exhast" but since I never checked the codes until now and I believe it has always had a small exhast leak since I bought it, it is possible that the Lean exhast code has been there the whole time, even when it ran perfect. I would like to solve the lean exhast issue anyways, but I don't think I have time right now to probe for the exhast leak and I doubt it's my main issue right now for boucing rpm issue right now.

Someone locally keeps telling my to try new spark plug wires. And I would like to try that. Problem is, I tried to purchase a set and all the new wires were about 6 inches longer than what is on my car right now, which means that the coil to cap wire alone would have a loop of wire since the one I have now is the perfect length. So does anyone recommend any local shops that sell the right length of plug wires? I don't want to order online and find out the online ones are also too long. (Even though they would work, I would like to match my current wires that are not only red, but the exact length that routes perfectly in the engine. The new wires don't need to be red, since I now have red loom covering over the wires because they clean up better than the wire and also would cover future non-red wire sets.)

Has anyone else heard idle improvements from new wires? Even though my car had a perfect idle the first 1.5 years I owned it, it just gradually got "off" and so I can't think of anything that may have changed to start my search. I will also try to post my efforts to try and help with ideas.

Haynes manual suggests worn camshaft or timing gears among other things.

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White 84 SE with the Duke, Holley TBI, Rodney's Cat

The stock spark plug wires (carbon core) I had on had only 3000 miles on them. I replaced them with MSD spiral core spark plug wires and it was like getting 5 to 10 hp.

I read you have no cat. If that is correct the O2 sensor may not be staying hot enough to remain in closed loop. Once the engine temp gets warm enough the ecm goes into closed loop and the O2 sensor is king of the fuel delivery chain. If it cools down too much it cannot work properly. When this happens you will see fluctuations in Idle and eventually the ses light. the light will usually be off when cruising or accelerating as there is enough heat to keep the O2 sensor warm enough to work. If you have a scan tool you should be able to see loop status and O2 voltage.

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Signature courtesy of MinnGreen.

[This message has been edited by Fiero STS (edited 10-22-2004).]

Well, I did finally fix the problem...I bought a Miata.

I loved the Fiero to death, but it was beginning to have more problems than just the idle. It will stay in the family, though, my father's buying it.

You can still put on a scan tool and check the loop status and O2 voltage. This will aleast eliminate some items. If it stays in open loop you will need to check coolant temp sensor. When you installed your new TPS did you verify it was in the correct range? It may be reading to high at idle. Also EGR and EGR solinoid should be checked.

HummelHund, I have owned several '87 & '88 coupes. I would be willing to bet money that your exhaust manifold is cracked at the welds where #1 & #4 tubes join the manifold. These cracks open up when the manifold warms up, and suck air into the exhaust. I know, that doesn't sound right, but it is. The extra air in the exhaust is picked up by the O2 sensor, and the computer will add gas to bring the mixture back into range. When that doesn't work, the computer does recognize the fact, and determines that the O2 reading is wrong, turns on the light, and disregards the O2 readings. That is when your idle stabilizes. But it seems the computer doesn't just forget about the O2 sensor, it tries every so often to use it again, then the whole scenario repeats.

The cracks are very hard to see with the manifold on the car. If you can get a bright light down there and use a mirror, you may be able to see some carbon tracks where the cracks are. The manifold is pretty easy to get off, the bolts don't seem to rust in the heads like they do on the sixes. Getting the manifold to the down pipe bolts off is another issue...

Pete

I read another post that suggests the exhaust manifolds can crack on the duke if water gets on them when they are hot but mine has the recall strip still on the back of the deck. My 87 is having problems and i am following (and posting) in them to keep this near the top to try to resolve them as cost-effectively as possible. that and i am getting tired of chasing problems. So far (for the sake of this thread) I have replaced the following: spark plug wires, PCV valve, crank position sensor, O2 sensor, catalytic converter and air filter. Today a fuel filter goes on. The car sat for a few years on a dealers' lot with no exhaust system and a variety of half completed repairs, some correct and some executed by a crosseyed syphillic baboon. The synptoms were/are: Hard to start (crappy gas i suspect) and backfires thru TB... and this is after the simple stuff the air filter and PCV - once it would start it wouldn't idle without several attempts to restart it. Then it would stall when put into gear (this is an automatic DIS 4 cyl) and once it would warm up enough to keep running in gear it had no power and the new catalytic converter would start to glow. Wouldn't go above 30 MPH. So in goes the new crank sensor some vacuum hoses and plug wires, the car starts easier and will idle better but still stalls and has no power. the cat will glow after a while still but not as bright. Still not much power, but now I get a code 13 = O2 sensor. In goes the new O2 sensor. Tiny better power amount but the good thing is the cat doesn't glow as bright. Now, I've mentioned the catalytic converter a couple times because it is NOT the manifolds but the cat! Would that mean something different than a cracked manifold, just running lean? i put a bottle of fuel system cleaner in the tank and I wanted to run a tankful through before changing the filter but I'm afraid of damaging the converter before then. If it doesn't run better after this I'm going to pull the EGR or replace coil packs next. The reason I haven't yet is there is already some shiney bolts holding the one on there down like it's been changed before I got it. From reading other posts I'll be switching out the ECM next and possibly the computer after that. Another tip I picked up is that the Torque Converter lockup solenoid might be stuck and is causing the stalling when put into D or R. I'll have to unplug that until I get round to fixing THAT headache.

[This message has been edited by USFiero (edited 02-19-2005).]

Well I hope this helps a little especially if you read through this thread. After doing some superficial repairs I tried to start the 87 duke w/auto and got the same results as before so in a nutshell I pulled two adjacent spark plugs and guess what: one was nice and clean and the other was all wet with gas - it WAS an ignition coil. replaced it and the car runs swell now. Still a little down onpower, but then again my normal daily ride is a V8 (too bad its not in a Fiero... yet)

quote Originally posted by HummelHund: My Fiero still idles poorly, and now smokes on occasion. Here's the scenario: Pull up to a stoplight, the car begins to idle roughly, bouncing between 700-1100rpm, stuttering, some smoke and it smells like it's running rich.

Mine would actually stall, and the smoking and rich smell sounds like fuel not burning... hence the idea it could be a coil going out. It certianly was with mine, at first. Replaced a coil, drove the car all day then it acted like the other coil was quitting. Now the car won't start at all.

Well, how's this for a bump? I drove the car for cbasically a day, it was weak then just quit running. I figured at this point maybe it was the PIM (under the coils) and per the Ogre's Cave I waited until a nice day came along and went to the junk yard and got a couple spares. They came with coils of course. The weird thing was the Crank position sensors were all screwed up on both... so I was a little nervous about these units. They were different from the one that came off my Fiero in that they had heat sink like fins all around the outside but otherwise they were bnolt ons. I swapped over my new crank sensor, lubed everything up with heat sink compound and bolted it in. Dang if it didn't start up right away! Then the exhaust started to smoke, it smelled rich. Got a Code 45 shortly after that and the check engine light would stay on. I unplugged the MAP sensor to make sure that wasn't the problem -- it didn't seem to help much. So my 'sensor safe' throttle body cleaner may not be after all. But the car runs with plenty of power, the cat doesn't glow, but now I am concerned about the long term effects of running rich. So it's parked again until I replace that TPS.

...replacing the TPS did the trick. Now I have to fix the new leak in the cooling system and oh-my-gosh this needs shocks all around. I'm also replacing the dogbone with an earlier style with poly bushings after reading Ogre's article in the cave. The old one was pretty worn. The Odometer on this car reads almost 190,000 miles.

bump

Since this is a popular subject thought I'd bump it up again. I wanted to be sure that I pointed out that the fuel filter needed changing early on (not sure this was plain in the rambling posts I made above) and that helped with the 'glowing cat' problem as well as the no power problem... besides all the other fixes listed. I have read that a couple people on this list advocate changing the fuel filter almost every year. In the position (down low) that it is at on the 87 I can see how it will collect junk, and it would be a special problem on neglected, sitting Fieros. Now the 87 runs pretty good, but I've put it in the garage until I get a chance to rebuild the suspension.. it is extremely bad.
I'm driving the 85 (duke) daily now, but I have a high idle issue there to chase down. It runs smooth and powerful, it just idles at 1800-2200 RPM all the time hot or cold.

i had a very similar problem with my 87 coupe for about the past year...finally got it to go away with a new map sensor and map sensor connector. Just a thought

I've figured out why my idle hunts, but have no way to fix it. While testing my car for emissions a few months ago I noticed that the HC climbed and fell with the RPM, and what I determined was that at idle at the low end of the spec the mixture is too rich. The ECM leans the BLM, that causes the idle to increase slightly. At the upper end of the idle spec the mixture is lean, so when the idle increases the mixture goes too lean, the ECM commands IAC to reduce the idle. The idle drops, but now it's too rich again, and the cycle repeats. I was able to watch the HC rise and fall in time with the idle speed. This was without a converter, BTW, so I was seeing actual HC output. I tried burning a chip that increased idle fuel, but my software created a bad checksum and the chip didn't work.

I'm still saving for a copy of tunercat, it will be a while before I can afford it.

JazzMan

quote Originally posted by JazzMan: I've figured out why my idle hunts, but have no way to fix it. While testing my car for emissions a few months ago I noticed that the HC climbed and fell with the RPM, and what I determined was that at idle at the low end of the spec the mixture is too rich. The ECM leans the BLM, that causes the idle to increase slightly. At the upper end of the idle spec the mixture is lean, so when the idle increases the mixture goes too lean, the ECM commands IAC to reduce the idle. The idle drops, but now it's too rich again, and the cycle repeats. I was able to watch the HC rise and fall in time with the idle speed. This was without a converter, BTW, so I was seeing actual HC output. I tried burning a chip that increased idle fuel, but my software created a bad checksum and the chip didn't work. I'm still saving for a copy of tunercat, it will be a while before I can afford it. JazzMan

This may seem like a dumb question...but im new to the Fiero abbreviations....what the hell is HC???