Random High Idle

Back over Thanksgiving I noticed one night when I started the Jeep that the Idle was way high, up around 2000 RPM. The motor was cold and it bounced around for a couple of seconds before it settled down to normal. That had been the only time it did it, so I thought that everything was OK and maybe it was just a fluke. Well last week it came back. I did some searching and saw to clean the IAC, as it might be sticking. I took it off and cleaned it with brake cleaner, and thoroughly cleaned the Throttle Body with TB Cleaner, and the problem went away again...or so I thought. It came back this week again.

It happens at random times, but most noticeable on the highway. If i'm driving around highway speed and take my foot off the gas, the RPM's are not dropping like they should, rather than staying at cruising speed. Because of this, the Jeep is bucking when I take my foot off the gas. Most times after a few seconds of waiting it will settle back down to normal and not do it again till the next time I take my foot off. However, if I put my foot back on the gas before it settles down, the Jeep bucks again. There are also some times where I come to a stop and it hasn't settled back down, or i'll be sitting at a light and it will randomly idle high.

I can usually pop it in neutral and floor it real quick and get it to settle down, which leads me to believe the IAC is still the culprit. The Jeep is running fine otherwise....just drove it a good 300 miles on the highway over New Years with the weird idle.

Before I drop $65 on a new one and that not be the problem, I figured i'd ask and get some others input. Thanks in advance!

Have fun......
http://www.naxja.org/forum/showthread.php?t=905849&highlight=high+idle

Yeah I read through that thread earlier....however I'm not dealing with a Renix XJ, so things like my TPS aren't adjustable.

I'm still leaning towards a failing IAC, but even though I just replaced the TPS a couple of years ago for other issues, I haven't quite ruled it out yet. Definitely have a few more things to check too such as loose manifold bolts, cracked vacuum lines...etc etc.

It couldn't be throttle mechanism/cable hanging up, could it?

I agree that the IAC is still suspect. Cleaning can restore functionality to certain failure conditions (carbon) but if it's mechanically failing, replacement is the only thing that is going to work. Unless you stumble onto another cause, I'd probably shell out for an IAC.

I looked at the throttle cable when I cleaned the IAC last week and it looked/felt ok.

I'm taking the Jeep on a 2 hour trip to the mountains tomorrow for a couple of days, so we'll see how it does. I'll probably go ahead and pick up a new IAC this week.

Figures today it's been running fairly well.

UNCC_99XJ said:

I looked at the throttle cable when I cleaned the IAC last week and it looked/felt ok.

I'm taking the Jeep on a 2 hour trip to the mountains tomorrow for a couple of days, so we'll see how it does. I'll probably go ahead and pick up a new IAC this week.

Figures today it's been running fairly well.

Click to expand...

I'am having the same problem with my 98 xj and i replaced my IAC a month ago. i think it might be faulty so let me know what you find out and i will do the same.

If it is not the IAC, then most likely is the TPS.

Drove it about 400 miles over the last two days, up and down mountains, stop and go city traffic, and it only acted up a little bit. I'll probably try the IAC before too long....have to buy books for school first and see what's left over.