95 Chevy 3500 w/5.7L...need help!

Tuesday (9 March '10) I went to start my truck and it did not have any get up and go and wanted to die in gear. The problem has only gotten worse. I have replaced the cap, rotor, plugs, wires, and air filter. I took the truck to a local shop and was told that "it's not a fuel delivery problem". Although when I looked at the injectors today, one seemed weak, drivers side. This truck will not idle in gear, dies at every stop and nearly dies in park if you don't rev it a few times. Any ideas on what may be the problem? I have put injector cleaner though it and at speed it does run better, guess I had better not hit any red lights.

Thanks, Craig

Next I'd check the EGR and IAC valves. They can get stuck from fuel varnish and sludge. Check, clean and/or replace. And I'd also check the ignition coil for good measure.

I checked the EGR and it moves freely, I even unplugged the vac line from it and there was no difference in engine idle. I'm not sure if this has an IAC or not. Also on an update, I replaced the pick-up coil and that helped a little and the vac line to the MAP sensor might have had a hair line crack in it. It seems as the truck warms up the worse it gets. Trying to get up to speed it tends to chug and hesitate and even dieing in "N". Right now it will idle at about 900 RPM when warmed up. I think running the injector cleaner though it made the gas pretty rich also contributing to the problem. I'm not getting any codes or check engine lights. I will put a meter on the ignition coil to see what the resistance is. This truck has me to the point that I would like to cut it in half and smash it.

Craig

From your 1st post about the drivers side injector being weak. If that is the case then only 4 out of 8 cylinders are getting proper fuel delivery. I have found that the best way to check TBI injector patterns is with a timing light (if the engine will run). If one injector is bad then both should be replaced as a pair.

As mentioned the IAC needs to be checked also (95% sure it has one on the TBI).

The ECT sensor (coolant temp to the ECM) needs to be checked also.

Hang in there. In a perfect world where nothing plugs up or breaks there would be no need for places like this forum.

I'm 99.9% sure you've got an IAC valve...since I have a '95 with a 350/5.7-L also.

The EGR is bolted into the intake manifold behind the TB on the passenger side. Forward of the EGR and screwed into the base of the TBI is the IAC valve, with a 4-wire electrical connector...about 1-1/4" in diameter. The TPS is next to the IAC towards the front, in line with the butterfly plate shaft and has a 2-wire connector.

If you clean the IAC, only clean the plunger part with carb cleaner or better use electronic sensor cleaner. Don't soak the electrical part of the valve in the solvent cleaner. Also, a used IAC can't be adjusted for plunger length...only a new one can.

Ditto on the ECT, and using the timing light to see the injector spray pattern.

Today, I unplugged the AIC and the truck ran good. I bought and installed a new IAC, plugged it in and the truck ran bad. I ran the truck at temp and even at 40 MPH so the AIC could reseat and nothing changed. It still wants to die in gear at a stop and in park. It gets worse as the truck warms up. So there is something wrong in the IAC circuit. What falls in line with the IAC? Any ideas?

Thanks, Craig

Today, I unplugged the AIC and the truck ran good. I bought and installed a new IAC, plugged it in and the truck ran bad. I ran the truck at temp and even at 40 MPH so the AIC could reseat and nothing changed. It still wants to die in gear at a stop and in park. It gets worse as the truck warms up. So there is something wrong in the IAC circuit. What falls in line with the IAC? Any ideas?

Thanks, Craig

somethings wrong with the engine vacuum ...the IAC is controlling the air entering the engine to regulate idle speed ...with a vacuum leak this throws off all these adjusting componets,,,engine runs poorly,,,,get a vac guage and hunt down the leak[s]...

Vacuum leak seems most reasonable. If the TBI to intake manifold gasket is the original, it may be old and swollen. There are some passages in the TBI's base that are sealed by the gasket. If it is old, it can become swollen and contribute to blockage if there is significant sludge. I just replaced mine because it had a big leak and it had nearly blocked the IAC passage it was so fat and swollen there, among other places. I'll post a pic of it when I get a chance.

Another thought is to check the wiring from the IAC to the VCM...make sure there are no breaks or shorts between them.