Ok, so far, in trying to get my 88' Coupe, 2.5L to run smoothly, I have replaced: MAP Sensor MAT Sensor O2 Sensor Coolant Temp. Sensor (replaced by prev. owner) EGR Valve All vaccuum hoses Plugs (AC Delco) Wires Fuel Filter Oil & Oil Filter Air Filter I've also decarbonized the engine using Ed Park's three part system.
Still, after all this, the car runs rough at startup, and once warm, the idle hunts and the car sort of coughs/hiccups. I've also noticed that under hard acceleration (I was in 3rd gear at the time, if that helps), it stumbles a little. The engine has good oil pressure and doesn't leak anything.
So. What's next to replace? My top suspects are:
Wires- I bought Autozone wires, which I haven't had problems with in the past, but those cars were not DIS.
Fuel Vapor Canister- It's original, maybe a source of vaccuum leak?
DIS Parts- A long shot, because from what I've read, they either work or they don't.
A PROM Problem- I was alerted to this GM TSB in another thread. Apparently the PROM can be a problem with these late model Fieros, and sometimes need to be changed? Anyone have any ideas on that? Link to the discussion: //www.fiero.nl/forum/Forum2/HTML/043407.html
The only other problem with the car is noisy timing gears. Could they be worn enough to cause erratic idle and the hiccups?
I am bound and determined to get to the bottom of this. Help!
Not sure as I don't own a 4cyl. but does your car have a TPS. If so that would be something I would concider replacing if not done yet!
I have noticed after replacing mine that I get a nice smooth idle (800-850rpms). My car (87 GT) also use to suffer from a very poor running condition when cold (it would stumble and hesitate while taking off). My car suffered from this for the better part of a year.....and I threw everything at it that I thought would correct it (plugs,wires,o2,egr,air filter,injectors,distribitor with rotor and cap, timming adjustments,even fuel filter and pump) but nothing did......so I gave up, that is until I decided to swap out the TPS from my 86 GT and low and behold it solved the problem and the real kicker was "I didn't even do it to solve this problem...I was trying to cure a high idle issue on the 86GT and was trying to rule this out".
Good luck!
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03:37 AM
HummelHund Member
Posts: 1037 From: Niceville, FL, USA Registered: Apr 2001
My 87 wasn't throwing any codes either so that was why I never considered it either. It was a surprise when I seen it fixed the 87 but at the same time upset me that it didn't fix the 86. Although the 86 problem is fixed now aswell (seems that when I pulled the plenum off to pull a head that I forgot to hookup a vaccum hose).
Not sure if there is anyway to test it or not either (short of buying one....and that would suck if it not your problem).
Good luck!
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04:12 AM
Pyrthian Member
Posts: 29569 From: Detroit, MI Registered: Jul 2002
I just replaced my alternator recently, and it got rid of my hunting idle. I have a underdrive pulley, and when my alternator died, I replaced it with a higher output alternator (SI to CS conversion) and it solved my hunting idle. But I had really LLOOOWW output before with the SI alternator. wipers would barely make it across the windshield at idle. But, anyways, ground & power will affect idle. See what your output from your alternator is at idle.
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08:46 AM
cool-tom Member
Posts: 23 From: Louisville, KY, USA Registered: Aug 2003
I have had idle problems and tested my TPS with an ohm meter. IIRC it showed 0 ohms to 5000 ohms in a smooth steady sweep. As I moved the TPS the meter followed every move, so I concluded it was working OK.
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09:20 AM
EMFORCE Member
Posts: 227 From: Lake Saint Louis, MO, USA Registered: Aug 2003
I recently had my timing gears and chain replaced (3.4L) and it seemed to help the idle a lot once warmed up. But, still , every once and awhile it decides to idle at 1500- 2000 RPM. there is no rhyme or reason to this- but it happens infrequently.
------------------ EMFORCE '88 Formula (Silver) 3.4 L, 5-speed Performance tires/wheels, sound system, electrics, exhaust, etc. (man I NEED new seats!!)
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09:51 AM
rube Member
Posts: 165 From: Indianapolis, IN Registered: Sep 2002
I don't think the alternator's the problem. Output is fine, and the unit itself is pretty new. I will check the grounds, though, that could definitely cause some idle trouble.
rube- Thanks for the link. The injector troubles mentioned in there seem like a very reasonable answer, I think AC Delco plug wires and a new injector are on my shopping list.
Thanks guys, keep the suggestions coming! If we can get all the possible reasons for a bad idle in here, it'll help me, and future Fiero owners!
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03:40 PM
TaurusThug Member
Posts: 4271 From: Simpsonville, SC Registered: Aug 2003
I doubt it's the IAC. Been there, done that. Done lot's of stuff actually. The IAC is one of those things that if it wasn't working you'd know it. If you hook up a cheap air/fuel ratio meter it will probably show wide swings at idle in time with the hunting.
Vaccum leak is probably out too, that would tend to be continuous. Gotta be fuel delivery somewhere.
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01:31 AM
HummelHund Member
Posts: 1037 From: Niceville, FL, USA Registered: Apr 2001
Thanks for the tip. The Ogre seems to back you up, from the article on the 700 TBI in his cave. He does mention a tester you can use for the IAC, if everything else is ruled out, I'll go that route.
Well, I didn't have a chance to change the injector out today, and now it's raining. The forecast is for rain tomorrow, as well. Having no garage or carport doth suck royally.
When the weather allows, I'll put the new injector in and post the results.
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01:48 AM
Dec 5th, 2003
HummelHund Member
Posts: 1037 From: Niceville, FL, USA Registered: Apr 2001
The injector didn't help with the idle, or the hiccup/cough/sputtering. Tomorrow I'm going to order some AC Delco plug wires(no one around here has them) and doublecheck my spark plug gap. I'll continue to post results to this thread, maybe my mistakes will help someone else further down the road.
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12:06 PM
OutlawFiero Member
Posts: 262 From: San Diego,CA,USA Registered: Sep 2002
I had almost the same problems on my '84Indy, mine would always hunt for idle and idle high(around 1300rpm), after replacing everything you did and even more, i finally replaced the rubber gasket that is on top of the valve cover, that(i think) went to the pcv valve hose. After replacing, car idled perfect!!! Ran a little better too. Not sure if this is you problem, but it could help, good luck!..jim('86GT)
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01:13 PM
Bruce Member
Posts: 2189 From: Ventura, California, USA Registered: May 99
Check the archives for the past month or so. I think someone ($Rich$ ?)posted that he ran a ground wire from someplace to another (no charge for the technical jargon), and that really smoothed out his idle. It was a simple ane effective fix. b
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02:08 PM
Dec 7th, 2003
HummelHund Member
Posts: 1037 From: Niceville, FL, USA Registered: Apr 2001
Ok, today I checked spark plug gap. A couple of the plugs were a little off, but fixing this did not solve my idle problem. I've got some plug wires on order, and they should be in tomorrow.
I'd noticed that sometimes when I turned my car on after letting it sit for just a few minutes, the idle would race up to 2500rpm, then after a 15-30 seconds, would come back down, and the SES light would come on. Today, the Fiero and I had a chat through its SES light, and I got these codes:
Code 13: Oxygen Sensor I've replaced the O2 sensor! Mayhaps the sensor's just confused.
Code 36: IAC Hmm....perhaps ManiMack was on to something...
Code 44: Lean exhaust Points to the O2 sensor and/or a vaccuum leak. The Haynes manual mentions the TBI base gasket. Mine is a little ratty, I may have to try replacing that.
Any tips based on my findings today?
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04:11 PM
PFF
System Bot
OutlawFiero Member
Posts: 262 From: San Diego,CA,USA Registered: Sep 2002
I think our cars have esp or something because that is also what mine does, and with the same codes. When I find a good solution I will post. I did do the extra ground, and it did smooth the car a little more, but not the idle problem. Because of the higher idle does your car also read about 500 rpm to high at cruising speeds also? I keep thinking and the car acts like their is some problem with a system/sensor that is not reading properly. So it idles, then jumps a little, idles again (high) and then jumps, and this goes on and on. I know what you mean by saying it's not a vacumm leak, I have had that before and this is not it. Something is not reading properly, or sadly it might be our ecm going bad.
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05:41 PM
rube Member
Posts: 165 From: Indianapolis, IN Registered: Sep 2002
look for vac leaks. read that article in my cave. Don't overlook the spare fitting to the left of the TBI unit.
sweep the wiring, especially grounds. Read Wire Service in my cave. Don't just look at them. take the grounds off and check each one. Replace the braied strap and run it to solid metal, NOT the bloody hinge stud like GM did.
DO NOT assume the alt is ok! have that and the battery tested. This can be done in car at Autozone, Sears, NTB, and many other places for free.
------------------ Be alert. The world needs more lerts...
Thanks guys. I'm going to give it another vacuum leak test, and then check the grounds. Come to think of it, the small battery to body ground that the Ogre speaks of in his cave isn't connected, I noticed that today.
I'll let y'all know how it works out.
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09:35 PM
jeffndebrus Member
Posts: 2772 From: Jacksonville, Fl- usa Registered: Aug 2001
I am sorry to hear that the 88 is giving you problems! Check the metal tubes that go to the fuel vapor cannister. I am not sure if these are "vacuum" or not, but I seem to remember corrosion at this point. The 86 is slowly coming along. I fixed the horn and wipers-both grounding problems. Still have to replace the heater core so I will have heat and defrost. Still setting a code 32 egr even with the new egr and braided egr tube. Bled the clutch and it is shifting pretty well now. Still have to sort out the wiring mess from the alarm system. Maybe someday I can get the radio to work lol. Good Luck!! Jeff
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10:11 PM
HummelHund Member
Posts: 1037 From: Niceville, FL, USA Registered: Apr 2001
It's been a good car, it's just got a few annoying problems that won't go away. I noticed those tubes when I replaced the soft hoses that come from them, I guess I need to get a can of throttle body cleaner and check for leaks in that area. I just came in from connecting the loose ground, and the idle problem is still there, though it does seem to run a little smoother (might just be in my head, though ). I've been reading about the 86', man, I didn't know it had that much wrong with it! I wouldn't have traded my 87' GT + cash for it if I'd known that. Good to hear you've got it going, though. You may want to take that EGR off and inspect it, make sure the last owner put it on right, especially if it isn't AC Delco. The aftermarket ones use a washer to fit properly, and if you don't get it on just right, it won't work. And the radio worked when I first got the car, then stopped working for no apparent reason. I didn't really look into why, maybe a fuse or wire connection?
One disturbing thing I noted while freezing outside, connecting that ground wire: My battery seems to be buzzing intermittently when the car is cooling down, then stops when it's completely cool. Is the battery going to explode? 'Cause if I have to have surgery to repair my face, I won't have the money to work on the Fiero.
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10:26 PM
Dec 8th, 2003
HummelHund Member
Posts: 1037 From: Niceville, FL, USA Registered: Apr 2001
Replaced the plug wires today, with AC Delco OEM. The idle problem is still there. I'm going to check grounds and vaccuum lines as soon as I get a chance. I think I'm also going to pull off the coil pack and inspect it and the crank sensor. I'm sure it won't hurt to have a new coat of dialectric grease. Will post the results as they come...
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08:04 PM
Dec 10th, 2003
rube Member
Posts: 165 From: Indianapolis, IN Registered: Sep 2002
Ummm...fuel? Seriously. An ignition system problem would most likely show itself as misfire/ backfire so I don't think that's your problem. Remote diagnosis is tough but I'd say look at the fuel pump.
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03:45 AM
Gordo Member
Posts: 2981 From: East Guilford, NY, USA Registered: Mar 2002
My 88 coupe has always had a slightly erratic idle with occasional stumble right from the time it was purchased new from the dealer. It was returned twice under warranty and they replaced the TPS both times to no avail. To this day, 72,000 miles later it still idles the same way. I have always just considered it the normal "nature of the beast" as my wife's 88 coupe also idles the exact same way. We have no drivability problems. They both accelerate just fine with no hesitation under load.
I might add that over the years, I have changed plugs, wires, coils, map sensor, pcv and the entire computer. It still idles exactly the same.
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[This message has been edited by Gordo (edited 12-10-2003).]
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05:35 AM
Dec 12th, 2003
HummelHund Member
Posts: 1037 From: Niceville, FL, USA Registered: Apr 2001
rube- I'm listening to ya. Buying a fuel pressure gauge is on my list of things to try. I REAAALLY don't want to have to change another fuel pump, but if it comes to that, I can.
Tomorrow I'm going to double check for vacuum leaks. I'm also going to inspect the coil pack and regrease its baseplate, and check the crank sensor while I've got it off. I think I'm also going to order the replacement PROM specified in the GM TSB and try that.
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08:29 PM
PFF
System Bot
Dec 13th, 2003
rube Member
Posts: 165 From: Indianapolis, IN Registered: Sep 2002
I would save my money and not buy the updated PROM. Think about this. The car did not have the problems your having when it was new. Nobody would have bought it. So, the problem has to be elsewhere since the car ran acceptably at some point in it's life with the current PROM. Dropping the tank is a pain but it might be worth it in the long run.
I've often wished GM had provided an access panel of some sort to allow changing the pump from inside the car (like an Eclispe). I hate being under a car on jackstands. Gives me a creepy feeling.
Easter egging with new parts sucks but sometimes you don't have a choice.
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02:50 AM
numan Member
Posts: 166 From: Kentucky, USA Registered: May 2003
I had a similar problem with my 84. I chanegd the O2 sensor with an after market brand. I blamed everything else until an old GM mechanic told me to install an AC Delco O2 sensor. He was right. Lots of new prts for no reason. It's GM parts for me on ALL my cars now!
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08:02 PM
Darth Fiero Member
Posts: 5919 From: Waterloo, Indiana Registered: Oct 2002
Not to overstate the obvious, but have you done a compression and leakdown test? If you have poor sealing valves they can cause all kinds of problems that not only show up at idle, but could cause problems under full throttle as well. With all the electrical and sensor work you have done, I am thinking your problem could be mechanical.
------------------ power corrupts. absolute power corrupts absolutely.
Once again, thanks for all the suggestions, this is helping a lot. It rained all day today, so I didn't get a chance to check for vacuum leaks. Tomorrow, if the weather's better, I will:
1. Check for vacuum leaks with throttle body cleaner. 2. Check and regrease all grounds. 3. Inspect DIS. 4. Inspect IAC. 5. Buy a compression tester/gauge and check compression.
I'll post my findings, we WILL get this thing running right!
Oh, and chcuk, I've used AC Delco parts as much as I can, including the O2 sensor, so I don't think that's the problem. Thanks for the suggestion, though!
[This message has been edited by HummelHund (edited 12-13-2003).]
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10:14 PM
Dec 14th, 2003
HummelHund Member
Posts: 1037 From: Niceville, FL, USA Registered: Apr 2001
They look like good numbers to me, any thoughts from the experts? I wasn't able to get any of the other tests done, other than a quick vacuum leak check that turned up nothing. I'm going to try to do a more thorough one when I get some time.
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04:38 PM
Dec 15th, 2003
ryan.hess Member
Posts: 20784 From: Orlando, FL Registered: Dec 2002
I'm not sure what the exact number is, but #1 is 10% lower than #4, which is a bit worrysome. However, two things come to mind that *need* to be checked/replaced, at least with some used junkyard parts to rule them out. TPS and IAC are two beasts that can test correctly and still be bad. (Okay, this is my opinion here, relating to experiences with a surging 93 grand am) TPS specifically has to be in a certain range or else the O2 will be so rich it'll set a code. IAC may be acting very slowly, causing a surging while it tries to match the idle rpm and "controlled vacuum leak". Hope this makes some sense, it's too early.