1991 chevy 1500 5.7 tbi erratic idle

[tpulliam79]

new iac and o2

[Jasper911]

I think I solved my problems today. I bought a used ecm from pull a part. It was actually out of an Astro but had the same service #. It runs much better so far and just for the heck of it, I've been playing with the e-proms from the 4.3, 5.0, and one from a Suburban that was either a 5.7 or a 7.4. The one from the Suburban just raised the idle and offered nothing performance-wise. However the 4.3 prom seemed to significantly improve power but smells a bit too rich. I'll drive it for a few days and see.

[tpulliam79]

yeah I tried new computer still no luck but after the work i have been doing on my 88 something occurred to me, the return line on my 91 from the throttle body is kinked pretty good, looks like someone tried to remove the fittings and bent it pretty good, now im wondering if the restriction in the line could be causing too much gas built up and may be causing my up and down idle? what do you guys think?

[NEUMANNZZ]

I would fix the kink.

[smblksrock]

CHECK THE EGR VALVE! At least take it off and clean all the carbon off. Alot of idle issues are egr's leaking or stuck open. This should be your FIRST suspect along with dirty IAC, then go from there.

[tpulliam79]

is there a gasket under the egr valve? think the kink could cause these issues? i am heading to the yard tues to grab a new return line.

[kavemanlee]

I have the same truck with the same symptom if yours is an automatic also. A local mechanic isolated it down to the probability of the gear selector sending mixed signals,ie; "I'm in Drive, now I'm in Nuetral, now I'm in Drive". I haven't tried to fix it yet but my idle remains mostly stable at 550 rpm if the traffic light isn't too long.

[tpulliam79]

sounds just like mine, and i have to hold the gear selector to the left if I want my reverse lights to come on. how is this fixed? I dont know that that is the issue with the idle but maybe I will kill two birds with one stone. If anyone knows how to adjust this please let me know ...thanks

[cancritter]

theres a adjustment at the steering colum in engine bay..losen nut and adjust accordingly...not shure this is what your after,,

as for kink in return line ..yes fix asp...if its bottlenecking return gas then it in turn is acting like a fuel regualtor and may be starveing engine

[tpulliam79]

the adjustment of the nut on the column in the bay will adjust the prindle ( for lack of proper term) and make the gear selector adjustment? I just want my reverse lights to come on when in reverse so people and cars will stop coming behind me as I reverse. and I am going to the yard tomorrow to get another return line.

[Jasper911]

My problem isn't solved either. I have tried three different egrs, one new, one from old engine and one from new engine before rebuild. All the same.

Still runs very rich. even blows a blueish smoke at times under load just off idle, but not oil smoke. This is unburnt fuel. The throttle body is the only thing I have never changed out and it has 255K. Possible worn throttle shaft giving false TPS info?

It will idle up briefly after letting up from giving it throttle. Also notice an oscillation up and down while parked in gear idling. At times under acceleration (from a stop) it hesitates then when I let off it responds. Like it's doing the opposite of my command. Annoying and seems hard on the trans and drive line.

[Jasper911]

Man

I kinda feel like a dunce. My vapor canister was leaking around the top. We checked it a while back, but not very well. I blew into the hose and felt the leaks. For now I just plugged the fitting on the throttle body. It's running excellent...duh!

[cancritter]

Originally Posted by tpulliam79

yeah I tried new computer still no luck but after the work i have been doing on my 88 something occurred to me, the return line on my 91 from the throttle body is kinked pretty good, looks like someone tried to remove the fittings and bent it pretty good, now im wondering if the restriction in the line could be causing too much gas built up and may be causing my up and down idle? what do you guys think?

as a general rule when you put in a aftermarket fuel regulator you put it in the return line....
the kink could be possible acting like a fuel regulator and starveing your engine...fix line and keep fuel lines as far away from exhaust or they will get hot and perculate giveing you same symptoms as a pluged or restricted fuel filter

[cancritter]

Originally Posted by Jasper911

My problem isn't solved either. The throttle body is the only thing I have never changed out and it has 255K. Possible worn throttle shaft giving false TPS info?

.

bang on with the throtle body shaft...gotta watch that on older tbis..even small amount of play is enough to throw things outa whack...for future refrence

[Jasper911]

I could never move the throttle shaft up and down enough to cause any idle change. It did have a bit of play but felt like every other one at Pull A Part. When it did change the idle, it was when I had gone past pushing and pulling and began turning it. I sprayed some starting fluid on the shaft as well and it never did anything to really take note of.

Now, this evening's discovery of the vapor canister is exceptional. Driveability is smooth and seamless. I knew something was up when the computer kept the idle high on a long test drive. I turned it off and restarted it. It now starts immediately and idles smoothly at the right rpm. It no longer burns my eyes or permeates my clothes when I stand behind it. The exhaust has a healthy ring to it. Damn, I actually look forward to driving it tomorrow!

Don't just check the vapor canister lines. Check the can too!

Thanks all. Now I can think about shocks and the bald spots on the roof!

[cancritter]

funny,,,had mine disconeted "canister line"..truck ran fine without but was thinking l'll keep re milage ect and a bumch of other things l dont know about...after readin this will definitley be keepin...speacialy after takein steel wool to line...nice and shiney now :O)

[Jasper911]

Grim update

Truck running better but still not right and still getting code 32. Drive for 10 miles or so and I get the light. Also, kinda doggy on the highway, does not run perfectly smooth and lock up (often premature(32mph)) makes it even worse. Have tried a fourth, known to be good, sucked on by me, oem egr valve. But still the same conditions.

Incidentally, the Autozone egr would not hold vacuum and my other oem egr was stuck in the opposite position and held no vacuum.

Bummin! Getting sick of this. Hate my truck.

[Jasper911]

Still fighting the demons!

[tpulliam79]

at this point i think im gonna live with it for now, had surgery on my right arm so for now its to be continued

[tpulliam79]

well now i feel dumb after all that has gone in to this truck i noticed it looks as if the balancer may have slipped so now im wondering if because of that i cant get the timing right and that could be the whole issue. I am having the balancer , distributor, crank seal, and cv done this weekend so i will update after that.