'96 cherokee - box stock

Engine has a nasty miss at idle and stumble just coming off idle. Engine has 171k on it and a cracked exhaust, crack is big enough to hear when cold but quiets when it warms.

I have recently done a tune up, plugs/wires/cap etc. Have looked for vacumn leak and can't any. Do you think the cracked header is causing the ECU to do something to cause the miss / rough idle?

I've had a cracked header for a long time on our 96 GC, and no issues with running rough. Welded it up and the noise was reduced, still runs fine. It seems, in theory, that the positive pressure inside the header would let exhaust out, not air in. I would look for other causes.

I'm having the same problems with my 97 TJ 4.0 w. 89k miles.

Mine rough idles but stops after I accelerate. I can hear it popping in the exhaust. Checked and rechecked the firing order. I changed plugs, wires, cap, rotor, and cleaned the throttle body thoroughly, the airaid spacer, and also checked for leaks in all the vacuum lines coming off of the intake. I recently replaced the front 02 sensor but I think the 02 after the cat needs to be changed also.

Problem hasn't been solved but people are telling me its either a bad Throttle Positioning Sensor or a bad Idle Air Control valve.

OkLaHoMaYJ, I have most of the symptoms you have except for the "pop". I also cleaned the throttle plate as best I could.

The injectors in my case have about 30K on them, so I don't think that's and issue.

If there's an issue with the sensors wouldn't the ECU throw errors?

All info replies are helpful, thanks.

Well in my case, my ECU will not throw a code (there is no code for a bad TPS on a TJ) if the TPS is bad. However, while I had the jeep running today I disconnected the MAP sensor and it threw a code immediately. 14 - MAP related issue. I put it all back together, reset the ECU, and it went away. My MAP is good but apparently there is no way of me knowing if the TPS or IAC is bad.

The IAC - Idle Air Control seems, atleast to me, to be my problem. It only occurs at low rpm's between 800-1500 RPM's. I might as well replace both and see what happens.

The TPS - Throttle Positioning Sensor may also be bad. I pulled it and cleaned it and nothing changed. It was loaded with carbon build up so it may be trash.