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Used Cars for sale - Used Trucks for sale [1334549052] Buy Used Cars

1991 Chevy 2500 5.7 Hard start, Rough Idle, No Performance

- Chevrolet-2500 Pickup

Forum Post
02/08/10 19:45
Randy Light

1991 Chevy 2500 5.7 Hard start, Rough Idle, No Performance

I have a 1991 Chevy truck 2500 with a 5.7 fuel injection throttle body. Has always ran great. Last October (2009) the engine was hard to start. When started, the engine idle was erratic. The RPM went up then down, up then down. After a while the engine dies. If you can keep it running and drive the truck, it acts like it's starving for fuel. You have to pump the accelerator to keep the RPM up. Now you can park, turn off the engine, same day or next day and it starts easy, idles perfect, and runs great. Then a day or two later the same thing again. I replaced the fuel pump and filter on the frame. This made no difference. Seems to do the same thing hot or cold days. No check engine light. Hope someone can help. Thanks
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This post has a total of 16 replies. Your feedback, comments, opinions and questions are welcome and encouraged.

This forum post has messages dated from 02/08/10 through 05/19/13, please be sure to read all the messages. If you feel it is old or outdated, please follow up with a question or comment and someone may be able to update it, or reply with newer information if you have it.

03/07/10 12:47
Joe Bassi

I'm currently having the same issue with my 1991 c2500 5.7 v8. The darn thing won't idle well and stalls. When it does run it has hardly any power. I replace the IdleAirControl valve, then the MAP sensor, replace all vacuum hoses. I did the fuel filter and check fuel pressure at 9.5 lbs. Still nothing helped. Then I changed the oxygen sensor, plug wires, plugs, new coil and new distributor and rebuilt the throttle body. Nothing seems to help it run better. I finally broke down and took her to a Chevy dealer in Troy Alabama. They had the truck twice for a total of three days and could not get it to run. They said without a check engine light or proper shop manuals that they were stumped. However they charged me over $200 for their time. Then I isolated the EGR valve and checked it over and it seems to be working fine. I even disconnected the EGR completely and that did not work. A friend of mine said that on these years of 5.7 v8's there has been a problem with a colapsing inner tube of the Y exhaust pipe. I did not know that the Y pipe had inner tubing. He suggested I disconnect the exhaust that the exhaust manifolds and run it. I have not done it yet but when I do it will be loud. I'm currently in Connecticut working and won't get back to 'Bama until April. If you find the answer let me know. If the Y pipe was my problem I'll let you know.
06/10/10 20:04

Similar problem 91 chev k2500 5.7. It seems as though mine only acts up when the engine is cold. I let it warnm up in am for 20 minutes or so then drive to work with no problem. I get off work around noon and dont let it warm up but for maybe 3-4 minutes then drive. The engines kinda stalls out just like you shut off the key then takes off again. drive for about a half a mile, it keeps stalling the rpm go from 2000 to 0 then back up to 2000 or however fast i am going then it dies. Smells like gas real bad. Let it sit for 10-15 min start it runs kinda rough then smooths out and runs fine when operating temp get up to 180-190. Any help would be greatly appreciated.
07/06/10 09:08

I have worked on a vehicle with the same problems as you, I had to remove the intake assy and replace the fuel pressure regulator, and yes its under the intake monifild
07/14/10 23:18

I having the same problem with my 1991 GMC Suburban 350 - 5.7, I started out with the map sensor, then rebuilt the Fuel pressure regulator ( Not Hard ), replaced the idle control valve, & Vacuum Hoses... If it was accessible I replaced it.. NOTHING WORKED unitl I put in a new Prom-Chip for the computer. Works great..
09/06/10 12:06
casey pye

i have a 305 doing the same crap and my buddy has a 350 doing it to and we just changing part that we think might be the problem as money well alow us but the salution im bout ready to go with is carburater 400 that will solve the problem and a want of more power to
09/22/10 16:33

Had same type trouble out of my truck at work (municipality). We changed plugs, wires, dist cap, ign module, every sensor. Still had same problem. Finally was under hood tinkering around with it running, moved wiring harness on intake and it spettered and died. Found the wires going to the temp sensor on top of the intake were either bad or the plug was bad. Replaced the plug and wires about 18 inches back and runs great now. Appeared this truck was flooding out, this sensor tells it to adjust fuel for the temp of the engine.
10/11/10 21:03

i have a k2500 with a 350 and it does much of the same more when its cold than hot but what gets me is i changed the fuel filter not to long ago and it improved performance but when its cold it just does not want to run. it stalls out all the time what would be the best thing to try first
10/19/10 19:26

11/16/10 19:27
matt giorsetti

if anyone has any idea i have a 91 chevy suburban w/5.7L engine and when its fully warmed up it missfires and the idle dropps real low then goes back up. I have replaced all the sensors on the engine and checked for a vaccum leak, cleaned all grounds and replaced the pcm, egr and catalytic converter. any help would be greatly apprietiated.
11/19/10 11:24
Big Dawgie

I have a 1989 Silverado 4x4, 5.7 that stalled and idle rough until it warmed up. It then ran fine. Check engine light stayed on constantly and the OBD1 code was 55. Very vague code. I changed Oxygen Sensor, Throttle Positioning Sensor, Engine Control Module, Fuel Filter, Fuel Relay Switch and Idle Air Control.

Nothing helped. I finally noticed a very small leak on the upper radiator hose at the thermostat housing. The Temperature Control Sensor Ground wire bolts onto the stud for the thermostat housing. The leak corroded/tarnished the washer and nut for the Temperature Control Sensor ground wire. I replaced the Temperature Control Sensor, nut and wahser. I also wire brushed the thermostat housing stud to clean it up. The truck started right up and runs perfect. Beleive it or not!

04/17/11 10:22

I really need help guys, I have changed everything mention in all of your posts and I still have the same problem. This truck has been my worst nightmare. it is a 1991 Chevy 2500 dually and I just cannot figure it out.. it will start and run rough and when I push on the throttle is will spitter/sput and die. I really need help with this problem. thank you
04/24/11 22:48

The distributer stem can become warn will not seal or stay in the correct position, replacing the stem could correct your problem. I'm not guaranteeing anything but this could help. This could be causing the misfires and rough running, which would be an ignition problem. The rotor in the distributer runs off of a shaft which is vertical in the motor and ties into the crankshaft.
05/08/11 21:52

Tim; Reply #6, thank for your post. I thought I had replaced everything. After reading your post about the temp sensor; I went out and diconnected it and the truck started right up. An easy $11 fix. Thanks
12/28/11 13:23
Buffalo, NY
Thank author of this post/comment"Temp Sensor"

I just want to thank poster #6 (Tim) for his advice. I had just about given up on my old truck when I stumbled on this forum.

Anyways, the temp sensor did the trick.

08/04/12 19:24
Salt Flats
Thank author of this post/comment"Low Idle Chev 350?"

I had this problem, where the motor will idle so low it nearly quits. I changed all of the componants I could think of, from the fuel pump, to the purge valve, up to the sensors, and then some. Well my Chevy Brothers, I stumbled on to a part inside the TBI. it is called the fuel pressure regulator. Fixing this solved all my problems. You will need to get a TBI tune up kit from your local parts store, (O'Reilly auto parts). It will include simple instructions, and pay close attention how you disassemble it. good luck!
05/19/13 15:25
Foster, ri
Thank author of this post/comment"need help"

If I block off my egr and unplug the solenoid will the check light come on , iam building a 383 for it so need help gonna be using a 4bbl intake with a composite adapter!?
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    Chevrolet 2500 Pickup '1991 Chevy 2500 5.7 Hard start, Rough Idle, No Performance'