I've got a 1992 truck with a 4 banger. Bought the truck with a blown motor so I rebuilt it. It starts perfectly and idles high for a minute or so then kicks down to a nice idle. It has an automatic and when I put it in gear it drops idle down even more. Not bad but noticable. It drives fine without any miss and has really good response especially for pulling 35" tires. Now the problem.... After its good and warm it idles really rough at a stop. No missing or hesitating while driving only at a dead stop. Only does this when the motor is hot. Im thinking maybe throttle position or mass air but wanted to check with you guys before going on a wild goose chase

 

I would give it a good tune up, make sure all of your hoses are good and no leaks, you probably have a lot of carbon build up from the EGR and it will have some plugged lines coming off of the Plenum. Then I would start running test on you different sensors if the problem persist.

 

vacuum leak on the brake booster/brake booster line. start there, easy to test, easy to fix, cheap.

 

Thanks for the replies so far. All the tuneup type stuff is new but I am going to check the hoses again. The truck doesn't miss a beat when driving just at idle after warming up. When cold its fine. I have worked on a few of these in the past but never had anything this aggravating

 

yeah. if the idle is high enough, a small vacuum leak won't be noticed. at a lower idle, it will. and when you stop (foot on the brake), the vacuum leak will be more noticeable.

 

So I got under the hood after a 15 mile trip. Can't find any hoses that are disconnected or appear to be damaged. I unplugged the TPS and the idle went back to normal except when I put it in drive then it goes low like I am putting a big load on the engine. For the hell of it I checked the tranny fluid and it was at the cold mark so I definitely need to add some. Did unplugging the TPS and idling nice in park prove anything?

 

Still need help here. Ended up replacing a few suspect vacuum lines and made sure the we're all hooked up good... No change so then I pulled the idle air control valve and it looked great. I put in hot water and proved it closed like it should then I let it cool down and it opened. What else is suspect here. It's driving me crazy! If I start it and let it warm up it idles fine in the driveway but starts acting up after driving about 5 miles. Rough as hell sitting at a light.

 

x2 on the booster!!!

 

Are you guys talking about the actual booster itself?I've checked the lines going to the booster and they are good.