strange running

Yes I have searched.

Have a '98 4.0L AW4.

After it's been running for a while it will sometimes (not always) idle up to about 1100 RPM when i put it in park or neutral. Runs smooth...just sometimes idles up higher.

For a few weeks now it will still do this BUT will also (again sometimes) idle low around 500 RPMs....but it also does it while in gear...not just in park or neutral like the high idle.

Just yesterday it tried to die on me...came back up on its own. Then about 100 yds further along it did die. No sputtering...nothing...just dead. Cranked it and it fired right up and kept going with no issues.

Today I was at a stop light and it idled down to about 200 RPM (again running smooth...as it can for 200 RPM). SO I shut it off...and cranked it...fired right back up and kept right on going no problem. This was all after driving around all morning for at least 40 miles.

I have a permanant check engine light due to a speedsensor issue so I canot tell if it;s throwing any more codes...and I intend to put it on a friends scanner but he's not back in town till tomorrow. So I'm entertaining even guesses right now as to what I could be facing.

Any update? My 98 is having similiar problems, high idle in park sometimes and and low idle sometimes when stopped and in gear. Does't do it all the time though. I cleaned the tb and it seemed to help for a little while but problem surfaced a few days later.

Anyone else have any ideas? Thanks.

Change the IAC on the throttle body. (Idle Air Controller) They can be had for about $30 or so at NAPA.

No codes at all. So if there's a sensor issue ...???

I did undo all the electrical connectors on the TB and put them back together. Since then it has run fine. No high or low idle and no stalling. I did disconnect the battery as wel to try and clear anything just in case. But like I said it;s been a few days and it's running fine.