94 Jimmy 4.3 CPI idling like crap
 

Hey guys, well my Jimmy has been sitting in the cold for about three weeks up until yesterday in my back yard. I went to go fire it up, started fine and ran smoothly. I went to go get some gas since I parked it with very little and about 2.5 miles later it starts running like crap, actually right as I let off the gas to pull into the gas station. It'll barely idle, the whole truck will shake violently and there is virtually no power brake assist at idle. And there is a terrible smell coming from the exhaust, I guess you can describe it as burning plastic and exhaust mixed together. Under throttle, the engine runs fine. I noticed that when I give 'er WOT for a couple moments, it'll idle fine for a little while but then start idling like crap again. It's been sitting for about 24 hours until now when I went to try it again and it still idled like crap, although I didn't drive it this time. The truck has done this a couple times before, but it has magically healed itself after a day or two. I actually got an SES light for about a minute during my ride yesterday up until I shut the engine off. It hasn't come back.

Wtf is the problem? I don't think it's a problem with an individual cylinder considering how it runs fine under throttle. Do you think the ecu might still have the trouble codes stored? If so how can I retrieve them (paper clip trick)? It ran perfectly fine before I parked it for the 3 weeks. I would start it up for a few seconds every few days while it was sitting with no problems. Maybe it's an EGR problem? I need it on the road soon....

some more background info on the car:
1994 GMC S15 Jimmy 4x4.
Vortec 4.3 CPI engine
Cap, rotor, coil, wires, and plugs all have less than 5000 miles on them.
About 150k miles with the original engine.

Thanks guys!

Sticking EGR valve perhaps? Or a dirty IAC valve?

A fuel leak could explain the symptoms as well, but something like that wouldn't miraculously cure itself. Low fuel pressure may also be a concern so a fuel pressure and leak down test isn't out of the question.

How is the system voltage during the problem?

Well that depends, when I'm coasting to a stop, the engine surges and the voltages surges with it. But usually when I'm stopped the engine just idles like crap, consistently but like crap. At that point, the voltage is usually normal.

I just ran a test on the SES light and it looks like I got a code 32, which is confirming my suspicion of EGR trouble. Now it's just a matter of me fixing it. I guess it's time for a new EGR valve!

You could try cleaning it first. :icon_wink:

That's what I'll do! I'm actually on my way to buy a new gasket. :)

Well i yanked the EGR valve off and I noticed that it was stuck halfway open. There was literally a 1/4 inch chunk of carbon wedged in the valve; other that that it looked relatively clean. So I got that out, sprayed it down with carb cleaner and reinstalled it with a new gasket. Went for a test drive and the truck ran beautifully for about a mile or so. Then slowing down for a red light it started surging again and actually stalled at the light. Fortunately it started back up (barely) and I limped home with the same symptoms.

So I'm thinking that the EGR valve might be toast; perhaps I even damaged it while cleaning it. I'll take it off again tomorrow to see what's up. I still think its the same issue considering how it ran great for a little after I cleared it out. So I'm guessing that the thing will open up but not close?

It is possible that another chunk of carbon got in there. I have taken to using a long brass pipe cleaner to clean the EGR supply pipe then start the engine momentarily with the EGR valve off and the port back to the intake plugged suitably. This will blow all of the loose junk out of the supply pipe.

Also, you should look into finding a screened EGR gasket for your application. It will keep the chunks out of the valve.

Thanks so much Swart! I removed the EGR valve again last night and sure enough, another 1/4 inch carbon pebble wedged itself into the valve keeping it stuck open. So I cleaned that out, and a ton of soot shot out when I ran the engine for a few seconds with the valve off. I got a screened gasket, slapped it all back together and the James now runs like a charm. :) I put about 25 miles on it in the past 24 hours with no issues at all. Thanks so much for the tips! I never even thought that a screened gasket existed. And here's a link for the gasket if anybody else needs it. :icon_wink:

http://shop.advanceautoparts.com/web..._A|GRP2037____