94 GMC Sierra starts, idles about 1500 rpm, will stall or sputter when accelerated, will have trouble restarting...replaced egr and iac valve. New fuel filter. Recent oil, plug, and wire change. Alternator 5 months old. HELP

Did you change the ECM to match the newer engine?

https://www.google.com/search?q=1992+GMC+Sierra+ST%2C+5.7+TBI+runs+rough

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sorry for late post
that was dead wrong to do. 1.6L ( 8v or 16v?)
the PCM sets idle only (ISC valve) and when cold only thermal IAC valve, so if then wrecked the TB throttle stop screw setting a factory settings. (no never touch) it did this like a CARB and is not one.

so is this a hot engine stall or cold, hot means normal temps.
stall on this car means the PCM lost control of idle. (its job is that)
top cause are.
1: EGR struck open they love to just as you stop the car. and stalls at 400 rpm and is never allowed to be active at idle (PCM logic0
so is bad valve stuck.
now back to high RPM
the answer is not same for 8v and 15valve engine
8v any vacuum leak causes super high idle.
16v engine leaks cause low idle, goes lean.
stalling has many causes ,
and are not the same hot and cold engine
on cold engine the IAC open and idle is about 1500 RPM
if not the IAC is dead or EGR stuck open.
on the hot engine the ISC holds RPM at 800 rpm, (AC off)
if not ISC stuck EGR open or ISC is jammed up,

EGR and ISC just love to stick on this car and can be cleaned
the IAC is therrmal device and can not be cleaned,only replaces and are rare now.
I have simple test to prove what it is , ask/

It can be issue with IAC( idle air control valve) causing the problem.

There are many other possibilities causing these idle issues. Engine idles rough.

There are few help links with solutions to troubleshoot such idle issues.

I suggest you refer the link below and follow its troubleshooting details:------

Click the link below:-----

Ford Expedition IAC valve replacing

http://technoanswers.blogspot.com/2012/12/ford-expedition-iac-valve-replacing.html

Bad miss at idle?

http://technoanswers.blogspot.com/2012/01/bad-miss-at-idle.html

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Stumbling and stalling at idle after engine rebuild?

http://schematicsdiagram.blogspot.in/2012/03/stumbling-and-stalling-at-idle-after.html

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1999 Ford F-150 Idles rough and quits when gas pedal is pressed less?

http://technoanswers.blogspot.in/2012/01/1999-ford-f-150-idles-rough-and-quits.html

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Engine stumbles coming off idle when warm?

http://repairhelpcenter.blogspot.com/2012/01/engine-stumbles-coming-off-idle-when.html

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Erratic idle on car?

http://schematicsdiagram.blogspot.com/2011/12/erratic-idle-on-car.html

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Cold start problem and vehicle shudder around 2500 to 3500 rpms

http://repairhelpcenter.blogspot.com/2012/10/cold-start-problem-and-vehicle-shudder.html

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Low idle when cold out side?

http://repairhelpcenter.blogspot.com/2011/12/low-idle-when-cold-out-side.html

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GMC Sonoma Stalls and idles low

http://technoanswers.blogspot.com/2012/10/gmc-sonoma-stalls-and-idles-low.html

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GMC Idle Air Control (IAC) Valve Replacing?

http://schematicsdiagram.blogspot.com/2011/12/gmc-idle-air-control-iac-valve.html

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1996 Camry intermittent engine failure while idle?

http://repairhelpcenter.blogspot.com/2011/10/1996-camry-intermittent-engine-failure.html

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Engine quits at idle?

http://repairhelpcenter.blogspot.com/2011/10/engine-quits-at-idle.html

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Car overheats and Air blows hot at idle?

http://howtobyme.blogspot.com/2011/11/car-overheats-and-air-blows-hot-at-idle.html

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High Idle Problem

http://repairhelpcenter.blogspot.com/2012/10/high-idle-problem.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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Idle flair is noticed on car? Rough idle? car will not idle? Erratic idle speed?

http://technoanswers.blogspot.in/2012/02/idle-flair-is-noticed-on-car-rough-idle.html

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High rpm in neutral? Inconsistant high RPM in neutral?

http://technoanswers.blogspot.in/2012/02/high-rpm-in-neutral-inconsistant-high.html

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Vehicle stumbling at idle and shows code 54?

http://schematicsdiagram.blogspot.in/2012/03/vehicle-stumbling-at-idle-and-shows.html

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Rough idle, staling and Erratic shifting?

http://technoanswers.blogspot.in/2012/03/rough-idlestaling-and-erratic-shifting.html

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While stop engine idles like cylinder missing?

http://schematicsdiagram.blogspot.com/2012/01/while-stop-engine-idles-like-cylinder.html

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These details will help.

Thanks.

Try replacing your Idle Air Control valve. I am a former Ford tech and have two LTC's a 94 and a 96. I have had to do this job on both. When they get up in miles, the IAC valve gets carboned up and can't adjust the air/fuel intake mixture under load. If you still have a stalling issue after that, then you will probably have to replace the EGR valve as well. But it is very important that you start the engine with the old EGR valve removed so you can blow any carbon balls out of the EGR passage before installing the new EGR valve. Otherwise you will just end up plugging and ruining the new EGR valve and have the same stalling issue. Good luck!

Hi, you've hit the usual causes. Now check for vacuum leaks and also for an EGR valve stuck open.

Please see my tip at http://www.fixya.com/cars/r7427423-fix_poor_idle_high_idle_stalling_fuel . These are generic instructions. If you get stuck or need specific instructions for your car, please get back to me with model, year and engine info.

Good Evening, have you double checked your timing and checked for possible vacuum leaks?

The throttle cable is probably ok. I would be more likely to suspect the idle air control valve/solenoid to be causing your trouble. Sometimes trouble with the EGR valve not closing all the way will cause this problem as well.

It is most likely the EGR (Exhaust Gas Recirculation) valve.
The valve is supposed to close when the car is idling and open other wise.

Inspect it / Replace it.

Hope this helps!

Throttle body, IAC or EGR valve.

egr valve