One day, while running some errands, my Jeep would not return to a normal idle and would only drop to about 1200-1500 rpms. A few blips of the throttle would get it back to normal at first.

I did a quick check for any cracked/broken vacuum lines and could find none. It seemed to run fine for a few more days.

Then it started again but at about 2000 rpms while I was driving. I had to slip it into neutral in order to stop and not fight the engine and returned straight home. Another check of vacuum lines revealed nothing.

So I went through checking linkages and sensor/ground connections. Still nothing. I had replaced the IAC (Standard Motors) 2 years ago and did a thorough TB cleaning back in May before smog check (passed) but decided to check them again. TB was still clean so I removed the IAC to make sure it was clean and the passage was also free of any build up.

That's when I noticed the oring on the IAC looked a bit ragged. Fortunately, I had a spare that fit so I replaced it. I cleaned the passage and the tip, put back together and SHAZAAM, all better.

Here's the old "O" ring: (sorry for the poor pics but you can see the shape).





208566

 

Good find!
I probably would not have suspect it and moved on to the TPS etc etc. Good to remember this.