I just bought a '94 Jimmy 4 door 4x4 with only 144k on it. The truck is in pretty nice condition and seems to have been taken care of for the most part. It has an occasional rough idle though. It doesn't always do it, and sometimes is worse than others. I have tried pulling the vacuum line off the brake booster to see if that made any difference to see if maybe it was a vacuum leak. Once unhooked the truck idled up like it should, and it tried to die when I plugged the vacuum line with my thumb. So I'm not suspecting a vacuum leak now. I also unplugged the IAC and the truck revved up and down and threw the CEL light on. I plugged it back in and turned the truck off and started it back and the CEL went off. The CEL light never comes on during normal driving, doesn't run hot, holds good oil pressure, and doesn't smoke or stumble on acceleration like I have read would be symptoms of a bad spider injection. Could it be an EGR issue? Bad gas? Clogged fuel filter? It has me confused since sometimes it runs perfect and always has good power and acceleration. Any ideas?

 

My EGR requires cleaning every 20000 or so. I put the aftermarket screen gasket in it from (UHelp I believe) and it seems to be better. Its easy enough to take off and inspect/clean so I would try that. If you have access to a simple scan tool, compare desired EGR position to actual and you'll know if they are not the same.


Another time I had a vacuum problem was the brake booster with an internal leak. Had to replace it.


In addition to the very common spider injector system issue (replaced mine 2x in 135K miles) , the fuel lines going into the manifold are notorious for getting hard with age and splitting. This will leak raw fuel into the manifold and can cause rich condition intermittently or you could lack pressure at the injector from this condition


Good luck

 

Thanks. I've let it get very low on gas deliberately so I can be sure I have good, fresh gas in the tank and I'm going to add some fuel system cleaner to it as well to see if there might be some trash in the system. I'll check the EGR as well and see if it needs to be cleaned. It likely has never been done. What's the best way to clean them on these trucks? With no CEL about the only other thing I can think of would be possibly a failing cat?

 

Filled the tank this morning and added a bottle of Lucas fuel system cleaner to it. I'll drive this tank out and see if it clears up any before I go crazy tearing things apart on it. Maybe moisture got in the gas from sitting? Maybe the Lucas will help clear out carbon...

 

You want to be careful running the tank very low on any car these days with electric fuel pumps, especially with aged fuel pumps. They rely on the fuel to cool them and I understand the most common cause of premature failure is from running the tank low enough to allow the pump to not be surrounded by fuel/coolant.


Hope the fuel cleaner does it.

 

You've never seen a "newer" fuel pump assy have u???? they basically sit in what looks like a big cup...as long as there is fuel in the tank they are surrounded...now I can see that being an issue with cars from the 80s' or early 90's i

 

Haven't had the chance yet to get it out and drive it much. I work about 5 miles from where I live currently. Have the next few days off, after my shift tonight. I'm going to try to put it out on the interstate and run it.

 

Like a 94 Jimmy?

 

Drove it out to my in - law's last night. About 40 mile round trip. Still running the same. Father-in-law said he thinks it's the iac. I think when I tried to check it I unplugged the tps instead.

 

My 93' had a similar problem. Replaced the dist cap and rotor. They can be bought together. Fixed it. 178k miles.