1990 Gmc Vandura Idleing Problem?

814jeffw · July 29, 2008

Hi, I have a 1990 GMC Vandura work van, 5.7,... and it recently began acting up on me. Always been a great work van for me. It will run ok to take it somewhere (Fortunately),...but every now and then when it is idling it will lose half of it's RPM's and then rev up and down about twice and then just die. But it will start back up and run fine as I begin to drive it. So far,.. (AC Delco) distributor and cap, rotor, ignition module, fuel filter and fuel pump. Oh yea,... and lots of head scratching. Also when you turn the ignition on to engage the pump it runs for no less than thirty seconds every time, should be about three seconds I thought. Don't know if this is part of the other issue or not. Would greatly appreciate any suggestions, and thanks!!

Jeff

mightybg · July 30, 2008

I have a 1991 k2500 5.7l, so I am going to assume the fuel control is similar. The fuel pump is supposed to run for 20sec with the key turned to the on position and eninge not running, this was to take care of hot fuel vapor lock causing starting issues. as far as the idle issue, i have read a few posts that have had similar problems caused by a bad ECM ground on the motor near the water filler neck or, like on my truck, on the intake bolt drivers side near the front of the engine. I have heard that the ground located on the water filler neck is a bad location for it and can cause problems. Or it could be the idle air control valve with controls the air density during idle operations and i think some off idle conditions as well. but I know for sure that it controls the idle speed with no throttle. (if you unplug it and start the engine my will run at ~1200 rpm instead of 750rpm).

814jeffw · July 30, 2008

Thank you Mightybg, I wasn't sure about the length of time the fuel pump was supposed to run. I will definitely check out the possible grounding issue. Will also check out the othe idle control valve you mentioned. Thanks again!!

Jeff