When I first picked up my 98 v6 manual 4WD, it had a rough idle... I cleaned the MAF, replaced the air filter, ran some seafoam through... and it was fine for about 3k.... now the rough/ high idle is back. Now when I am sitting at a stoplight with the truck in neutral, it idles as high as 1300 rpm. Then again, sometimes, it idles perfect at the 600-700 rpm level. What gives?

Also today, the check engine light came on.

I had changed the spark plugs when I first got it, and cleaned what I described above, so I am at a loss for what could be causing this new condition. Any ideas? Thanks

 

could be your tps or you ISC valve. (idle speed contol). I just replaced one on a 97 with the same problem

 

Is the idle high all the time, when the engine is hot or cold? Mine runs high when it is cold (probably to heat up quicker), and I imagine most other do as well. I think I idle at about that speed when I first start it up in the day.

 

I'd bet money it's the later (IAC valve) of the two also.
You can try cleaning it and see if that helps.

Search on YT for IAC and you'll find a few threads on how to clean it.

 

Will do...

Just to check, I cleaned the MAF again before going out tonight, and it still did it.

(And no, its not just when cold... its all the time... 5 minutes after startup to 3 hours after highway driving)

I also noticed tonight, if I tap the throttle a bit, the revs will sometimes drop a few hundred rpm before darting around a bit then settling around 1000 rpm.


I will definitely check for the IAC valve cleaning procedure... I hope its not too bad.