My Fiero Formula is idling irratically when you first start it thru the first 5-10 minutes of running. Then, after it warms up it runs perfectly! When idling poorly, in park (ATX) it will idle up and down, sputtering when it goes down and occasionally will stall, but not often. When put into reverse with a cold engine, the RPM will drop so low it will stall or nearly stall. When shifted from P to drive, it usually doesn't idle down as far, but will occasionally stall. It will idle fine when moving, but the idle will drop and be irratic, close to stalling when stopped at stop signs, street lights etc. These problems will disappear once the engine gets to normal operating temperature. It will sometimes idle up and down over about a 100 RPM range while stopped or in park and warm, but this isn't too bad and is no way close to stalling the car.

Since this has been an ongoing problem, I have had many mechanics look at it and a lot of stuff has been repaired/replaced. Here is the list.

Complete tune up...
Dist. cap and rotor, plugs, wires, ign. coil, air filter, PCV valve, charcoal canister filter

EGR Sys.
Repaired vacumn lines and fittings to eliminate leaks.
New EGR Tube
EGR Valve
IAC valve
MAP sensor
Throttle body cleaned

Anybody with any ideas? Since the problem changes based on engine temperature, I am thinking it might be mechanical. Fuel injectors maybe? Or timing chain? Other sensors could be the EGR solenoid or Lock up solenoid? Maybe I am wrong, but I wouldn't think these components would be temp sensitive.

Any help would be greatly appreciated. I am now at a loss as to what it could be, and taking it to mechanics isn't getting me anything but diagnostic costs which turn up nothing. I hope somebody can give me some advice. Thanks!

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John
AOLIM: Fformula88

1988 Fiero Formula
1985 Fiero SE 2M6

Have you already performed a basic idle speed setting procedure. This is done while the engine is hot and the IAC fully closed. You have to turn the manual idle speed screw up enough to achive the desired RPM. The screw hidden under a plug which you must remove to make the adjustment. After you do that then the TPS sensor needs to be re-adjusted correct.

This may help.

Put ECM into Diagnostic Mode (jumper the top far right 2 ALDL connector pins) with key on-no start. Disconnect the IAC plug, then turn off key, remove ECM from diagnostic mode (remove ALDL jumper), start engine with scan tool attached or Tachometer installed, set idle to 650 to 680rpm. When completed shut off engine reconnect IAC plug. Turn key back on and re-adjust TPS to proper setting. Then clear ECM trouble codes by disconnecting the battery.

The 650 to 680rpm IAC setting is approx 100 rpm below the commanded chip program, and also becomes part of the stall saver.

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86 SE Fiero converted to GT (Buick Turbo V6 transplant in progress)

78 Malibu 3.8L Turbo Buick
TURBO WONDER
Best 8th: 1.548, 6.62@106.32 3450lb
TE-70 3 bolt, Ported Stock Iron Heads and Intake
2.5 stock intercoolers
Vernon Swindell, Jr.

Thanks for the advice Turbo... but I am not sure where the idle screw is located. I've been looking around the throttle and there doesn't seem to be any cap or screw there to do this. However, I don't think the idle speed is really the problem. Sometimes it will idle fine.

The car is also running a bit rich when idling bad... which is probably causing the stumbling. I've also replaced the MAT and coolant temp sensors without any improvement. Since it was running rich, I thought maybe it was adding more fuel do to faulty sensor readings of either of those two... guess not.

In fact, its idling worse now. It will start, run at about 1300 RPM or so... idle back to about 1100. Then it will start to stumble, the idfle will drop momentarily and return to 1100... eventually one of these drops is enough to stall it out... sometimes it saves itself and comes back up.

1 of 3 things .. TPS,MAP,IAC once had the same problem .. after telling myself repedidly that it just couldent be the throtle posisioning senser and after replacing almost every electrical part ..shure enough it was the throtle posisioning senser

I'll try the TPS tonight. For the more expensive electrical stuff, I've been swapping parts between the SE and my Formula since the SE is running great, and most of the stuff is interchangeable. If its not the TPS, I am going to be totally lost! I bought a new IAC and swapped the MAP... no success. Thanks fldevil!

Hmmm...Im having the exact same prob w/ my Formula. I havnt driven it in a while because of that. I makes me very nervous at long red lights. It was running fine, then the day after Christmas, it wouldnt start. It would turn over but not start. I had already replaced all the ignition components. Now it'll usually start (most of the time), but from time to time it does that bizzar idle thing like yours does. I was thinking cold start injector, but that thing only fires when the starter is doing its thing......who knows. Youve gotten me really courious again about it. Ive pretty much ignored the Formula for the past few months, with the exception of starting it up about once every two weeks or so. Hmmmmmmm
M7F

quote Originally posted by Fformula88: I swapped the TPS... no luck. Anybody have any other possibilities?

I ended up having to have my injectors reconditioned before I was able to fix my problem which sounds like it was similar to yours. Rough/stalling when cold and surging idle!

I was thinking it might be the inectors too. However, I am not sure that explains why it stalls when shifted into reverse. Its as if the transmission is putting such a load on the engine when it goes shifts into gear that it stalls. If I give it gas as I shift, I can keep it running.

My7... does yours stall or almost stall when shifted into gear too? I don't know if this is a symptom or cause, just curious. I haven't driven the my Formula much either because of the problem. If I let it warm up, I think it will stay running. However, those first few miles are troublesome! I am going to keep playing with it... if I figure anything out I'll let you know.

Does anybody know if the injectors can be tested without removing them from the car? Can a computer diagnostic troubleshoot the individual injectors? Thanks all!

I have a 88 Astro vanthat had the same problem took it to several mechanics spent tons of dollars on diagnostic machines still didn't work.Went to the parts store and just happen to see this old fart shade tree mechanic friend of mine and mentioned the problem to him and he said change the water temp switch what it does is to tell the computer to send more gas ,i bought the part put it in and bingo ran great after that just my 2cents.

Thanks for the advice Bluemagic. Unfortunately I've already replaced all the coolant temperature sensors and such. They didn't seem to help any. No luck yet.

Sent you a picture through e-mail.

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86 SE Fiero converted to GT (Buick Turbo V6 transplant in progress)

78 Malibu 3.8L Turbo Buick
TURBO WONDER
Best 8th: 1.548, 6.62@106.32 3450lb
TE-70 3 bolt, Ported Stock Iron Heads and Intake
2.5 stock intercoolers
Vernon Swindell, Jr.

I think you said that you had changed all the coolant sensors. The main sensors is the ECM sensor just under the thermostat housing and the MAT sensor located in the air cleaner housing. these two sensors tell the computer the temp of the air and water and to adjust the fuel ratio.

<~~ Got the pic! Thanks. I'll try playing with it tomorrow.

ka, I replaced both of those.

Just sending back to the top in hopes of any other ideas.

Ok call me krazy but is the alternator putting out enough juice. My 88 did idle ocillations but when I replaced the alternator and battery the problem went away. I read somewhere that at low rpm the alternator is not putting out enough to charge the battery and run the ECM and all the other electronics to keep the car running so the IAC kicks up the idle and thus more juice to the system causing the IAC to bring it back down again. This continues until 1 of 2 things happens. 1 enough electricity to run the car (battery charged enough) or 2 STALL!

My 88 now starts and Idles HIGH (up to 1300 rpm) then slowly comes down to normal as it warms

Like I said its a far fetched solution but it worked for me.

I just went through some papers on my car and found I replaced the alternator and the battery CHECK your battery first since it may be weak! but still crank the car over. Chances are that the battery is the culprit

[This message has been edited by 84Bill (edited 04-07-2001).]

Fformula88, one thing no one has mentioned to you is the O2 sensor - it should probably be changed - this could cause it to run rich. Since yours is an automatic, you may want to change the Automatic Torque Convertor Lock-Up Solenoid. This will involve removing the transmission pan (might as well replace the filter too while you are at it) as the solenoid is located inside on the bottom of the tranny. It is possible that the torque convertor is not fully releasing when stopped at a light, sign, etc and this will cause the engine to attempt to stall.........

I think the electrical is good. The guage reads fairly normal when the car is on, and the battery puts out plenty of power to crank the car, even when its cold out. So I'd be doubtful that is my problem.

tgowens, I was thinking maybe the lock up solenoid too... or possibly the P/N switch. Yesterday after work I tested the P/N switch according to the Pontiac shop manual and it tested ok... so that leaves the lock up sol. The O2 sensor is new, so I think I'll try the solenoid next. I know I need a fluid change and new filter in the tranny anyway.

Thanks again for the advice!

Try swaping the O2 sensor with the known good one from your other car. It,s possible that it was defective when you installed it.
The O2 will cause eratic idle.

Just bringing this back to the top...I seem to be having the same prob...just wondering if there are any updates?

Thanks...

I thought I read in the Haynes manual that the o2 sensor does not feed the ECM any info until it reaches 600 degrees or so. If this is true then it should have no effect when the car is first started. "The ECM will not react to the sensor signal until the sensor reaches approximately 600 degrees Fahrenheit. This factor must be taken into consideration when evaluating the performance of the sensor."

No updates from my end so far. I still mean tot ry and swap out the lockup solenoid, but haven't had a chance to start working on that yet. I've been driving the car a lot, which seems to have had a small effect on the problem. It hasn't stalled on me since I started to drive it daily. It still idles very bad, and comes close to stalling, but keeps running. I dunno if its dumb luck or not. TThe car IS running very rich when its cold. Until it warms up, the exhaust is a little smokey when it is first started and when I give it gas. I think this is related, but am not sure on what is causing.