I've been slowly trying to fix my 1998 Jeep Cherokee 2.5L 4cyl. The engine revving has gotten terrible. It idles high then kicks when put into drive. Starting the engine sometimes takes longer than usual and requires a few tries. Sometimes it shakes a bit or a bunch.

I replaced the TPS because the check engine codes pointed to it and the gas pedal response now is clearly much better, but that didn't solve the cold start and poor idle performance. The check engine light is now off (amazing!). I adjusted the idle screw on the throttle body to close the butterfly valve more, so I could have it idle in Drive nicely. That meant I had to hold the gas just a tad while the engine warmed up from a cold start, otherwise it would idle lower and lower and die. The thing was that after driving a while, the idle would perform well (maybe a slight bit too low but it wouldn't die).

I got a new IAC from pepboys. The tip, the connector, and the body are the right shape and size, but the stem is much shorter than the one on the old part. See http://imgur.com/1nE6JdA for a picture of the parts. The top one in the picture is from the car, the bottom one is the one I bought. I don't know how much the tip is supposed to move, so I figured maybe the old part has the tip out and the new one has the tip in. I installed it and adjusted the idle screw to bring the revs up because they were way too low. Now I get a decent idle in drive, but the park idle is way too high and gives the car a big kick when shifting into drive. Occasionally, the park idle is not ridiculously high (but still high) when I start the engine. The changes in revs in Park as well as in Drive over the course of a minute are all over the place.

Question:

What do you make of the difference in stem between the old and the new part?

Any chance the new part is the correct part?

It's very hard or impossible to find anything online that looks like the length of the old part that is currently in my car. Maybe it's broken and stuck in the 'out' position so it doesn't let air in and that's why I have to tap the gas a bit to prevent the engine from dying at idle.

Help me make some sense of all this. I've been Googling a whole bunch and replacing the TPS has been the only meaningful improvement so far.

If it's any help, my throttle body has a part number on it that reads "53032016AC", which searching online makes it seem like a generic throttle body for various brands of cars.

 

There are two different ones available, 1 for a 1998 only 2.5L, and then the 1998 with a 4.0L / 99 with a 2.5L. The shorter one is correct for the 1998 model:
http://www.completecherokee.com/prod-871.htm
Here is what the longer one for the next year up is:
http://www.completecherokee.com/prod-872.htm

It's possible that someone installed the later model on your 1998, assuming that the VIN & engine are correctly a 1998 model (and not a late 98 that was issued as a 99).

 

The OEM part number is 53030820, which when new, looks like the bottom one in the pic.

The top one in the pic looks like the same body and pintle as the bottom one but the pintle is stuck all the way out.