Chevy & GMC Vans

Ok, some of you know who I am, some of you don't. Im Dennis, skippys brother. As some of you know, Im having major problems with my van. The major problem is, no idle. It will not idle correctly, it goes up and down, even when I help it stay running by pressing the gas pedal, as of late, it is NOT throwing any codes from the computer. here is a parts list of what has been replaced, and fixed.
timing chain and gear, idle air controller, electronic spark control, throttle position sensor, coolant temp sensor, throttle body has been rebuilt, with new fuel pressure regulator, and rebuild kit, intake manifold gaskets replaced, egr valve, plugs, wires, cap and rotor, computer and chip,map sensor, all engine and body grounds have been checked and fixed where needed, all vacuum lines checked and replaced as needed. It has been put on a scan tool numerous times before, which led us to the esc at first. Its not a timing, its not a fuel pressure issue, I thought vacuum, which is why I replaced the intake gaskets, Im lost, 2 other reputable mechanics are lost. So here I am. Countless hours,money, and much stress later, we've gotten nowhere. when you start it, it will not idle on its own, it bogs like itsnotgetting fuel, or too much fuel, or too much air, but everything, according to the hand held scan tool, is within spec, again, no codes from the computer now. PLEASE HELP!!!!!

what year van? what engine?
Are the injectors spraying like they should?

Battery & alt have been replaced , fuel pump & filter also grounds have all been checked , 3 different computers & chips with no difference . power cable from battery to starter was replaced . compression was tested its got 120 to 122 on all cylinders . all electrical componants have been replaced with new or known good parts . throttle bodys been replaced & rebuilt . everything in the dizzy was checked or replaced . its got good spark cuz it will fire right up , but won't stay running unless you feather the gas peddle . fuel spray pattern at the injectors are perfect , no drips or misses . egr has been checked countless times all hoses for vaccum checked or replaced . the diaphram for the cruise was bypassed cuz i thought maybe the diaphram went bad but nope .

any suggestions you can think of would be greatly appreciated . we're all dumbfounded !!!!

oh yeah its a 1992 astro 4.3 with TBI awd .

Does it have the hydroboost or vacuum boost power brakes?
If vacuum, there may be a leak inside the booster.
When the IAC was replaced, did you check the pintle diameter to ensure it matched the original? I've been given the wrong IAC, that bolted right in coincidentally. It worked for a while then gave up the ghost, and never did throw a code.
Man what a problem. That pretty much taps my ideas.
Time for the heavy duty gurus to chime in.

vaccum booster hmmmmmm didn't think of that . how could you check it ? i have the one from my 88 it should bolt right up correct ? the IAC yeah we made sure it was correct & even adjusted it a million times to see if it made any difference , & no difference .


nope its hydroboost !!!!

skippy wrote: fuel pump & filter

this was gonna be my question, all though most of you are far superior mechanics than myself, did you possibly try another new fuel filter just incase?

Skippy,
Am I mistaken,but I thought you have this fixed before.Did it go back to it's old ways over time??.

Time to look at the long shot problems because looks like you have the normal stuff covered.

yes fuel filter was replaced 3 times that i know of maybe more .
gary , this is sortof an extention of the problems it had before . it was remedied last time by putting in a new coolant temp sensor . it would only act up once in awhile after that . & at wierd times . it seemed to act up after long trips (more than just around town , like more than 10 constant mile trips ) it would idle shitty & stall at lights .then the next day it wouldbe fine for awhile . untill finally it wouldn't idle at all & if it did idle , it would run like crap & die as soon as you dropped it in gear . its still running like that now .

It's running worse than that now, even feathering the pedal, it wont run more than 30 seconds. Even spray from both injectors, good fuel pressure, new pump, sending unit and filter, tbi was rebuilt and a new presuure regulator was put in. The only thing not replaced yet, is the 02 sensor, but there is no catalytic converter. And it absolutely will NOT run in gear.

Just a shot in the dark, but perhaps you have a leak at the intake manifold gasket or throttle body gasket. How do the plugs look? I'm not sure how you would check for it in a car, but on motorcycles, we would spray the intake manifold with starting fluid, or brake cleaner, where it mated with the head. If there was a leak you would notice a drastic change in idle. Don't spray in or near the throttle body opening, just around the gasket sealing surfaces.
If it running as bad as you say it is, you will probably need one person spraying looking for the leak, while someone else feathers the gas.
Hope it helps..

This is a wild guess,but replace the gas tank cap with a new one.I am not kidding,just try it.

Anyone in the tri-city area know voodoo?

liftedwhiteastro wrote:The only thing not replaced yet, is the 02 sensor, but there is no catalytic converter. And it absolutely will NOT run in gear.

Well, here's a few more thoughts..thinking "out loud" here:
It's certain then that it's not a clogged cat. However, the O2 sensor is the primary sensor for adjusting the lean / rich fuel mixture. The ECM won't take readings off the O2 until it goes into closed loop operation. If the O2 was functioning just barely within spec so as to not throw a code, but causing the fuel mix to run lean, you wouldn't see the effects during warm up, then as the engine came up to operating temp and the ECM goes into closed loop, you might not see drastic effects untill the engine is good and heat soaked, at which point the incoming air is getting pretty warm resulting in lower density. combine that with a lean fuel delivery and you have a poorly running engine.

dunedog wrote:Anyone in the tri-city area know voodoo?

Not sure if there is anyone but skippy has access to 1/4 sticks of dynamite!

Good luck on getting this fixed Dennis and Dan.