Hello everyone,

My 98 Classic does not like to idle when it's warmed up. I know there could be a variety of problems that could cause this, but I thought it would be worth a shot if I said something here. It's not bad enough that it sounds like the engine is going to die, but it may drop a 100 RPM and then shoot back up to normal a second later. It's not throwing any codes, either. All suggestions are appreciated

 

Are you getting any codes? Don't quote me on this but on most vehicles I've owned they won't idle nice if I keep it below 3k. On the highway home I like to hit 4k-4500 for a bit to "burn off the carbon build up" and by the time I get to the stop light at my exit it's idling smooth as butter. It's something I learned in a auto forum at one time or another

 

Nope, no codes. I usually take it easy with the Jeep and the engine never revs over 3K. Soon I'm going to pour some Seafoam in there once I get a new tank of gas. Hopefully it helps.

 

You might want to try cleaning the idle air control valve. They can get gunked up and effect your idle.

 

That's most likely your problem. Rev it up to 4500 a few times on a nice highway trip then report back.

Funny story, the last engine I used seafoam on to help with a rough idle blew the head gasket. I'd look at the iac and motor mounts before pouring snake oil in your motor and crossing your fingers.

 

Sorry it's been so long, I've been awfully busy and only got back to the Jeep the other day. I used some SeaFoam and did some around the town cruising in 1st gear. Seemed to have helped a lot, and I think I'm going to clean the idle air control valve today when I get a chance.

 

Always worth checking the basics. I chased a warm idle problem for a year, fixed it and then it came back. first time was spark plugs. I replaced the champions with autolite. Idled ok cold, was fine at speed, but terrible idle when warm. 6 months later had another warm idle problem. Turned out to be the coil that time. I had proactively replaced the original coil with an Echlin from Napa. I always keep the original parts just in case. swapped it back in and has been great.

 

Agreed on cleaning the IAC and it's wire connector. The TPS can affect throttle also, any funny business shifting also might point there. TPS does not like getting wet, if this started right after a wash might point there also.

 

I'm going to be reviving this thread because my problem has returned. It has gotten bad pretty quickly (maybe over the course of 2 weeks). I was pulling down my driveway (just idling) and the Jeep started sputtering and jerking around. I shifted into neutral and it was still doing it, so I gave it a little gas (up to 2K rpm) and it eventually smoothed itself out... Put it back in drive and it's idling fine for a 5-10 seconds, sputters and drops 100 rpms, and then returns to normal. This process does not stop. I restarted it several times but the problem did not go away. The check engine light did not turn on. Any help?