I know this is common with fieros...what's the fix.... engine starts...runs.....after it warms up it starts to surge ...rpm gauge runs up and down until it eventually shuts off....anyone??

IAC - Idle Air Control located below the TPS on the side of the TB. The IAC is either dirty and or it is bad. It unscrews from the TB. Unplug the wire, take it out and try cleaning it with carb cleaner. Look at the end of the IAC. Make sure that the point is clean and does not have any pits or heavy deposits on it. When you first pull it out, the sealing surface of the plunger will be evident. Make sure this area is clean. The ECM see's a rich/lean indication from the sensors and adjusts the IAC in or out to compensate. If the IAC is dirty, sticking, etc. the engine idle will "hunt". At idle, the butterfly in the TB should be closed. Air for the engine is regulated through the IAC port. In the front of the TB inside at the bottom, there is a hole apprx 3/8". this is where the air for the IAC port enters. Be sure to clean this port out too. Also, get some pipe cleaners or small round fiber brush and clean the port that the IAC screws into. For me, I have found it best to take the TB off and clean the entire TB. Once it is all cleaned up, reinstall and see if that cures your problem. If not, try a new IAC. It could also be the TPS going bad too. The TPS could be sending a false signal to the ECM fooling it into thinking the throttle is moving up and down then the ECM compenstaes with either fuel through the injectors or opening the IAC for more air. Of course it could be due to other sensors or combinations of sensors but I have found that the IAC/TPS is a good place to start. You will also want to check for vacuum leaks.

A couple of questions:

Does it only do this at an idle?
Does the car "surge" while driving at a steady speed?
While driving at a steady speed and you left off the throttle to say come to a stop, does the engine die or try to die?
What does it do when the AC is switched on? At Idle? At steady Speed?

[This message has been edited by katatak (edited 08-21-2008).]

thank you for a very informative post...to answer your questions...it surges only after it warms up...and it when it is sitting there idiling...and at red lights..anything else you can think of??

Thanx again

Good info there. Let me know if you solve the problem, cause I have a similar issue.

[This message has been edited by MarineFiero (edited 08-22-2008).]

Has the TB "idle screw" (not what it really is) been messed with. It should still have a cap on it so you can't see the screw.

Sometime messing with it can cause the idle hunt.


Has it alway done this for you? You will often notice it hunt more with the air temps are between 50*-70* or so.
Hotter and colder then that and they sometimes don't hunt.
When mine does it sometime if I blip the throttle so it snaps shut quickly it stops the hunt. I have not figured out if its the change in the TB butterfly position, TPI, so some other sensor that sees a change from doing it..

[This message has been edited by Dodgerunner (edited 08-22-2008).]

Often times a surge can be traced down to one of two things, running lean, or a slow O2 sensor. Fuel is used in combination with the IAC to control engine speed. When in closed loop, the O2 sensor is what keeps the fuel in line. If it's reading slow, it can be like pushing a person on a swing at the right time- it starts to oscillate more and more. Of course, it's hard to tell for sure without a data log.

quote Originally posted by ryan.hess: Often times a surge can be traced down to one of two things, running lean, or a slow O2 sensor. Fuel is used in combination with the IAC to control engine speed. When in closed loop, the O2 sensor is what keeps the fuel in line. If it's reading slow, it can be like pushing a person on a swing at the right time- it starts to oscillate more and more. Of course, it's hard to tell for sure without a data log.

Like ryan stated, sounds like something could be fubar with the 02... Since it's only doing it when the car warms up, that's when the car enters closed loop... Do you have a way to put a scanner on the computer and see how the 02 is reacting? Is the coolant temp sensor working correctly as well? Do you have a vac leak? During cold start you usually run richer to help warm the engine, so it's possible that the car is rich enough not to surge with the vac leak during cold start, but once it gets to the base fuel map it's too lean with the vac leak.... Check all your vac lines etc and see fi anything is up.

EGR valve can cause a surge problem also and on some OBD I vehicles can be caused to malfunction as a result of other sensors being out of spec. In other words try disconnecting and plugging the EGR vacuum line at the EGR and see if it helps.

I actually changed the egr valve and have noticed that the O2 sensor is on its last leg...looks rotted and corroded...I am rebuilding the car and do not drive it everyday but do notice the surge every time I turn it on..... I am going to start with the O2 sensor

quote Originally posted by mavsf49: I actually changed the egr valve and have noticed that the O2 sensor is on its last leg...looks rotted and corroded...I am rebuilding the car and do not drive it everyday but do notice the surge every time I turn it on..... I am going to start with the O2 sensor

The EGR can be pulsed inappropriately as a result of a problem elsewhere so changing it would not stop a surge if it is not the primary cause. It will still cycle on command by the ECM. It does appear the O2 sensor would be a good start.

Good info everyone,

I just went through all the IAC, TPS, vaccuum leaks, etc. It did make a difference but I still get some idle hunt after it's warmed up. I just got back from a 60 mile drive and in town, it would ocaisionly die at a stop light. I also just did some datalogging with help from Dodgerunner. My 88 is doing this intermittently and ocaisionaly will throw a "lean" code. When it does hunt at idle, I also notice that it lags between idle and 25-2800, I think the data points to the O2 sensor. I got to change it out and see if it makes a difference.

Pat

When you do change it out, report back. It helps to have people say "I did everything but then I did this and it worked"...

Keeps this topic going. I have the same problem with mine. I just did a 3.4 conversion and started to have the same idle problems. I've checked for vacuum leaks, have new Bosch O2 sensor, new IAC valve, and cleaned throttle ...everything is close to new. I even replaced ECM. I was told to reset idle to 750 rpms by adjusting idle screw with air intake rubber tube off and obstructing the bottom hole in the throttle. I will do this tomorrow to see if this will reset the base idle and then go from there. Any comments and suggestions greatly appreciated

.

quote Originally posted by vitog44: Keeps this topic going. I have the same problem with mine. I just did a 3.4 conversion and started to have the same idle problems. I've checked for vacuum leaks, have new Bosch O2 sensor, new IAC valve, and cleaned throttle ...everything is close to new. I even replaced ECM. I was told to reset idle to 750 rpms by adjusting idle screw with air intake rubber tube off and obstructing the bottom hole in the throttle. I will do this tomorrow to see if this will reset the base idle and then go from there. Any comments and suggestions greatly appreciated

Skybax wrote an excellent article, had it book marked, on setting base idle screw.
https://www.fiero.nl/forum/A...060206-2-060970.html
I will say this from experience, you'll do a little bit better if you have a scanner or "auto x-ray" rather by doing this blind.

mavsf49, I'll agree with the above posts. I prefer a AC Delco O2 sensor over a Bosch, they seem faster and helped tone down my hunting idle on my old 87GT. Be sure to double check all your battery and ground connections, sensors and ECM won't operate well with crappy power.

quote Originally posted by vitog44: Keeps this topic going. I have the same problem with mine. I just did a 3.4 conversion and started to have the same idle problems. I've checked for vacuum leaks, have new Bosch O2 sensor, new IAC valve, and cleaned throttle ...everything is close to new. I even replaced ECM. I was told to reset idle to 750 rpms by adjusting idle screw with air intake rubber tube off and obstructing the bottom hole in the throttle. I will do this tomorrow to see if this will reset the base idle and then go from there. Any comments and suggestions greatly appreciated .

I have heard just the opposite - not to touch the idle screw - it is actually a stop screw to keep the butterfly from jamming in the bore.

quote Originally posted by katatak: Hope the old one comes out easy. Any suggestions on reinstall? Should I use some anti sieze? First attempt at dealing with the O2 so I am a little hesitant.

Spray some PB Blaster on the threads & let it stand awhile. A good O2 sensor wrench helps -- the one I found fits over the sensor and has an offset socket to fit a 3/8" ratchet. If you find yourself holding a ratchet handle in a way that, if things break loose suddenly, is likely to cost knuckles, do the smart thing and get a neighbor to push on it while you stand back and observe. A cheater bar helps immensely -- I had about an 18" piece of PVC pipe at hand that happened to be large enough to fit over the ratchet handle, tried it on a whim, and broke the thing loose fairly easily without loosing any skin. (All hail PB Blaster!)

The hardest part is disconnecting and re-connecting the lead wire -- it should be a one-second, two-handed job with the car on a lift, but on a jack when you can only get one hand to where the connector is, it takes some effort.

Guys, thanks for the input. Jetman, thanks for your link. I think itt will make my job easier. I'll let you all know how it goes. By the way, here's a link on idle and leak problems: http://www.justinchristie.ca/blog/category/fiero/

quote Originally posted by katatak: I have heard just the opposite - not to touch the idle screw - it is actually a stop screw to keep the butterfly from jamming in the bore.

For all intent, that is correct. If the cap has not been removed or tampered with, it is best to leave this alone and not touch it. The ECM expects to see the throttle body in a certain position through the count from the IAC in the idle position. The ECM will have fits if this is out of whack so you don't want to mess around only if you really need to. I posted the link to the skybax article so people will have a decent procedure to follow if they needed to reset the throttle body.

quote Originally posted by vitog44: Jetman, I checked the auto-x-ray scanner . It runs about $200. Can you suggest something cheaper. Will any OBD1 scanner do the job? Thanks

I usually borrow the scanner form work so unfortunately I cannot make recomendations. Auto parts stores have tool loaner programs, I wonder if they have one available? I want to get a scanner too and will be using the forum search to see what the other members opinions are.

quote Originally posted by katatak: I have 2 extra O2 sensors that I will try in the AM. I will go run a few logs and report back. Hope the old one comes out easy. Any suggestions on reinstall? Should I use some anti sieze? First attempt at dealing with the O2 so I am a little hesitant. Thanks

Definately use anti-sieze on the threads, careful not to get any on sensor tip. Badly rusted O2 sensors can be removed by heating the bung with a torch and quenching it with PB blaster, repeat a couple of times. The heat will draw the PB blaster into the threads.

quote Originally posted by mavsf49: I know this is common with fieros...what's the fix.... engine starts...runs.....after it warms up it starts to surge ...rpm gauge runs up and down until it eventually shuts off....anyone??

Failing MAP sensors may also cause the surging idle. Try removing the connector to the MAP sensor to see if that makes a difference. You'll throw a code but you can clear that out by disconnecting the negative battery cable later.

Use only throttle body safe cleaners when you're cleaning parts, no sense frying your O2 sensor.

------------------
jetman
Silver 86 SE 2M6 4-speed, with "check wallet light"
Now fortified with 8 essential slices of bacon goodness

Ok, I could not get the other used O2 sensors out of the y Pipe's so I broke down and bought a new O2 sensor. I could not find an AC Delco off the shelf so I got the Bosch. Also picked up the "tool". I have the old one "soaking: rigt now. I will give it a go when it cools off out side this evening.

Pat

Just got back from a few log runs. Installed new O2 sensor. My "lag" is much better and no O2 lean code. Still have a slight idle hunt. I pulled the IAC and it was filthy. I cleaned it off and reinstalled. Getting better with each little tweak. Next I will pull the TB and clean it up. If that don't work, I will try the Idle adjustment procedure and see what that gets me.

Thanks for the reply Jetman. found a neighbor who has a skanner. I'm still going to try the manual way to reseg idle today. Please keep the postings coming.

Ok folks,

Here's what I did today:

Pulled the TB and gave it a thorough cleaning. Th IAC ports were filthy and the tube that runs from the TB to the manifold was almost plugged with crude. Also the TB butterfly was pretty nasty especially on the intake side. Pulled the IAC out of the TB and gave it a real good going over. Reinstalled everything, Performed the adjustment of the IAC, disconnected the battery, etc. After I got it all back together and the ECM reset, I went for a drive.

I can not believe the difference. Wow..... Rock solid idle @ 900 RPM, No surge what so ever. All the lag between idle and 2500 - Gone. Car runs and pulls hard all the way to 5k - thats where I let off......

After I ran some logs yesterday, I sent them to Dodgerunner and he suspected that my IAC was dirty and not reacting quick enough thus my issue with the car dying when I decelerated to a stop. That issue is cured too.

Sometimes it is the simplest, easiest things that make the biggest difference. The only sensor I replace was the O2 and it made a difference too. Here's what my weekend fix its cost.

Bosch O2 Sensor from Autozone - 19.99
Can of carb cleaner - 4.00
Can of PB blaster - 7.00
O2 sensor tool - priceless - 9.00

So for 40 bucks, I got a lot taken care of.

Thanks to everyone that had a suggestion. Big thanks to Dodgerunner.

Pat

Wow, that's good news to hear and thank you for posting that follow up information.

Still waiting for mavsf49 to post on his results, did you make any progress?

Ok its been a while but her eare the results...changed IAC...TPS...O2 sensors...Installed ceramic coated crossover pipe and cleaned out throttle body...does not surge anymore...pretty steady...however I thought the ratlle I heard was coming from the crossover pipe in bad shape but it seems its the alternator making a racket...I knew I had to change it because my new baterry kept on dying...big improvment however...does not burn lean any more...going to try to replace injectors and CAT next

quote Originally posted by katatak: Ok folks, Here's what I did today: Pulled the TB and gave it a thorough cleaning. Th IAC ports were filthy and the tube that runs from the TB to the manifold was almost plugged with crude. Also the TB butterfly was pretty nasty especially on the intake side. Pulled the IAC out of the TB and gave it a real good going over. Reinstalled everything, Performed the adjustment of the IAC, disconnected the battery, etc. After I got it all back together and the ECM reset, I went for a drive. I can not believe the difference. Wow..... Rock solid idle @ 900 RPM, No surge what so ever. All the lag between idle and 2500 - Gone. Car runs and pulls hard all the way to 5k - thats where I let off...... After I ran some logs yesterday, I sent them to Dodgerunner and he suspected that my IAC was dirty and not reacting quick enough thus my issue with the car dying when I decelerated to a stop. That issue is cured too. Sometimes it is the simplest, easiest things that make the biggest difference. The only sensor I replace was the O2 and it made a difference too. Here's what my weekend fix its cost. Bosch O2 Sensor from Autozone - 19.99 Can of carb cleaner - 4.00 Can of PB blaster - 7.00 O2 sensor tool - priceless - 9.00 So for 40 bucks, I got a lot taken care of. Thanks to everyone that had a suggestion. Big thanks to Dodgerunner. Pat

How (or what) exactly is an IAC adjustment? I read about the 1 1/8" distance from the pintal to the shoulder, how does it adjust?
sparx22