91GMC Sierra won't idle

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#1
Hey guys....I have another problem...think I am getting to old for this crap....my mind isn't working like it should....anyway...91 GMC Sierra, 1500,4x4,4.3.....came in running like crap and wouldn't idle.....I put new plugs, wires, cap, rotor,fuel filter on it....still wouldn't idle...I changed the IAC....still no idle...Starts right up and if I give it gas it will run good at high rpm....let of the gas and it dies....start it up without touching the gas pedal and it starts and revs then the idle comes down and it dies......any thoughts are appreciated.....Jim....
 

nickb2

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#2
Hi, jim, long time, no speak, I am pretty sure you have this info but will post anyway. Maybe I read wrong, but is this manual or auto trans? Cuz specs and idle counts are different and pcm relearn is different.

I have not worked one of these in years. ouch Is it a K series or

Also did not see any codes written in your initial post. Try to see data on short/longterm fuel trims. :idea:

But those old scanners are hard to find, can use DVM on AC scale :idea: Shorting A and B pins on DLC should give a code :idea: Post back I will be most happy to help!!!! 8) :thx ;D

I still don't why when I post, I am 1 hour back. How do you fix that? Anyway, maybe an admin can help me with this pesky little detail.

I added another pdf, may help. :p

Had to modify, key words here a fuel trim and IAC count in this TSB ace 2 attachement. 8)

Still had to modify, I forgot to write "know" :ROFL
 

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billr

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#4
Have you checked the ECT sensor? Easy to do with just an ohmmeter. GM has used the same calibration for years, the calibration chart you find for any GM will be correct. Then, how about compression, fuel pressure, and ignition timing? Yeah, ignition timing may not be adjustable, but still can't hurt to check what it is doing at idle. Is the IAC trying to slurp in air at its inlet port? Another easy test to see if IAC is even trying to work.
 
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#5
With KOEO look at the injectors- are they leaking -spraying ?
check the inj harness as it passes thru the air cleaner assy they can rub to ground.
Be sure the EGR is seated - 4.3 is bad for pintel stuck open -
 
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#6
Thanks Bill....I changed the ECT.....same thing...fuel pressure is ok....timing looks close.....didn't do a compression check.....Kev....injectors aren't leaking...wires look ok......pulled the EGR...cleaned it....looks to be seating ok......drove it around and when stopping at a light it idles ok.....come back home and let it idle in the driveway and it dies.....maybe a bomb would help...lol....Jim
 

billr

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#7
There is an O2 sensor on this? Does it go and stay rich or lean as the engine struggles to idle and dies?
 
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#8
That comment starts revs idles down then stalls - would have me looking at vacuum-Check for vacuum leaks- TB base gasket, Intake, Temp disconnect and plug the EGR vac line,


compression, vacuum reading steady, plug appearance black-wet -dry- tan?