Hello, I just got a 2001 Cherokee Sport with 186k miles on it as my first car and need some help. I'm getting a P0121 code as well as P0300, P0301, P0302, P0303, P0304, P0305, and P0306 codes. The engine idles rough (swings from 750 to 1k and all the way down to 300 rpm before shooting back up to 750rpm. When I drive it, the transmission is having a hard time staying in any gear other than 1st (it'll shift into 4th for a bit, then shift down to 3rd and constantly switch between the two). The transmission also will only shift back down to 1st after coming to a complete stop and sometimes wont shift into 1st until after setting off (sub 10mph). What could be causing these issues? I checked the transmission fluid and it was way over (1.5 dipstick reading) so I think that may be causing part of the issue but i don't know for sure. I will be taking out the transmission fluid (along with every other fluid) and replacing it. I am also installing a new transmission filter (and replacing all other filters too). As for the P0121 and the misfire codes, what could be causing the issue? Is it just a bad TPS sensor, or something else (coil pack or spark plugs), or a combination of problems both mentioned and something I may have missed? Any help would be greatly appreciated and I can't wait to get this thing on the road!

 

Don't bother dropping the transmission pan just to replace the filter. It's just a metal screen and doesn't need routinely replaced. You are checking the level with it running, after cycling through the gear right? You can measure the trans solenoid resistances to get an idea if they are bad. A bad TPS or a poor adjusted throtltlebody-to-transmission cable can cause shifting issue. Search youtube for bleepjeep's video on adjusting the cable. I think he has one on testing the TPS with a voltmeter too. Also remove and clean the ground point by the dipstick where a whole bunch of grounds converge.

 

Yes I am checking it after cycling through all the gears. I also went through the service records and the TPS sensor was replaced just before Covid hit in early 2019 and hasnt been driven much since then. How would I measure the trans solenoid resistances? I will check out BleepJeep's channel, thanks!

 

Here ya go!

 

There are two connectors in the engine bay up against the firewall for the two harnesses that come up from the trans. One is for the NSS that senses what position the shifter is in on the passenger side,. The other has the speed sensors and solenoids on the drivers side. The solenoids should be 11-15 ohms to ground.

 

Started up the car today and it had the roughest idle I've heard it have, but its also the coldest day i've started it up. Once the AC motor came on the rough idle went away. With the AC off the rough idle came back and stalls in park several times. Barely putting pressure on the throttle it kept on stalling. With more and constant pressure on the throttle, the revs would not stay constant: they ranged from 1500-2700. I revving at 3k rpm for 3-5 seconds and let go of the throttle, and it went down to 300 rpm then went back to the rough idle. Unsure if that helps y'all but giving more information. The TPS sensor has been replaced recently as I said before, and my father (who's done quite a lot of work on all of our cars) is pretty certain it is a vacuum leak, but curious what y'all think

 

Sounds like a vac leak to me as well. 20 years old could have dryrotted or nibbled rubber hoses. Have you cleaned the throttle body including the port where the IAC mounts? Just because the TPS is a year old doesn't mean it's not bad. There are way too many low quality replacement parts out there, often bad right out of the box or fail within a year. Something to keep in mind when replacing instead of testing parts (aka firing the parts canon).