2001 Cherokee, will not idle. Only runs if accelerator is depressed to 1000+ rpm, afterwards idle is rough but acceleration is great. Turn key off, restart, condition returns. Large watery black discharge from tailpipe also. I'm thinking IAC or clogged cat. Has been scanned with no codes coming up. Replaced CCV which fixed it for a while but condition is back now after about a month. Any suggestions?

How about the Throttle Position Sensor if they get wet they will act really odd.
OH yea do not try to water proof it with anything that will penetrate the unit (it will ruin it they cost about $75.00). If you are concerned about water getting to it, even from washing the engine, use WAXYOL can be found on the internet (of course)

The first thing to check is the vacum hoses - mine will idle at 1100 if
I have a hose off somewhere - they are hard to track down - but if you
have them all locked down then it is three sensors to check - MAP - up on
the fire wall - Throttle Possition - and the other thingy on the throttle
body.

If you have check your vacum lines then I would suspect
that this is the MAP - up on the fire wall - or one of
the vacume control items on the side of the intake .

The TPS is so bad on 89-91 Cherokees that there
is a RECALL...

IAC motor will do that.Changed a few of those out on the 4.0s.

IAC = Idle air control

If you pull your battery - and then - reconnect
it you should hear the Idle Air controler click
loudly - other than pulling it out and checking
to see if it is seating - the most common problem is oil being pulled in from the PCV/line and coating the intake - and the IDLE - so the best you can do is to clean it.

The older TPS can removed and you can check that it has the proper voltage on the power input 5V and the correct output at idel .8 V .

It turned out to be a bad battery. Registered well during tests but did not have enough juice at idle to run the fuel system. Replaced battery, all is well.