I have a 2000 Jeep Cherokee XJ 4.0L With an automatic Transmission. 202k miles and around 4 months ago or even more (sometime during the summer) my XJ would get to temperature and at red lights it would start dropping RPMs and then jerk forward as the RPMs would jump to 1000 and would be fine after that. It stopped doing that for a couple months. Just recently started dropping RPMs and almost stalling again but this time sometimes it won't have any throttle/acceleration and then the transmission would slam hard and it would take off. Today while I was driving it started to drop RPMs once again and then had not throttle/acceleration and it would not regain throttle. I pulled over messed with a few things and then started the motor and it idled fine in park. Once I started driving again it was losing power and throttle while driving and then it would go back to normal I pulled over again knowing something wasn't right and it would drop RPMs and have no throttle. Had someone come meet me and drive it home so I could get back to work and there was no problems. I got home and checked for vacuum leaks, loose wires nothing was causing anything I drove it around the block and it started to drop RPMs again. I kept it in Drive and it drops rpms I put it in Reverse, 1&2, 3rd, Drive, and Park it drops rpms almost stalling but in neutral it idles fine. Ive ran the codes and had a o2 sensor code and a input speed sensor code got rid of both still having the same problem. I've clean the Air idle control valve, and throttle body. I replaced my battery almost a year ago. I've checked grounds. Replaced the fuel pump recently. I'm definitely not a mechanic by any means. I know about cars but definitely not a mechanic. I also changed the spark plugs and boots recently.

 

It sounds like it could be a problem of your throttle position sensor (TPS). A fault in the TPS could definitely cause it to drop RPMs while driving, and the TPS has a direct effect on transmission shifting characteristics too. This is what I would want to test first, but with those symptoms you are saying it could be a lot of different things.

 

Yep, but TPS is the place to start. Testing is easy.

Search the forum or YouTube for info on how too test it.

 

I bought a new TPS sensor and replaced the old one last night. Still having the same problems. Except my Jeep is pulling a large amount of air into the air box. Never seen it pull this much air.

 

1. Testing is easy, and much cheaper than just blindly buying parts.
2. Aftermarket sensor are often garbage, and may not work out of the box. For Chrysler products, stick with the factory stuff. You can find them sold under the Mopar label, or the NTK label, or NGK label.

I would do two things at this point (in this order):

1. Test the TPS. Yes, it's new, but if it's not Mopar, it's still suspect.
2. Check the TPS wiring. Can't get a good reading if the wiring is going south.
3. Adjust the transmission kick-down cable. Not a strong suspect, but it's free and easy, so, why not? You might need to spend a few minutes (took me about 10) and some penetrating oil getting it to move freely, but that aside, it only takes a couple of minutes. Literally, less than 5 (not counting the time you spend to watch the video).
4. Check your fuel pressure. Rent a gauge.

 

Your problem is almost guaranteed to be catalytic converter beginning to clog. I've been dealing with this exact issue for a couple weeks and just yesterday evening I cut mine out and the instant I cut it out I got in and started it held the brakes put in drive and it wound up to 4500 RPMs.... Couldn't get above 1500 before.......

 

This is my drill, because I'm bad at guessing - get your shop manual. Assuming your air filter is clean, spark plugs, cap & rotor and wires are good, check for dangling wires grounding. The wires coming up from the O2 to the fuel rail wiring harness are a good place to start. Then open your shop manual and test your sensors: the temp sensor, idle solenoid, MAP and TPS. In my experience, the crank position sensor is good - or you stranded by the side of the road - but test it anyway. If they are good and your throttle body is clean, move to the injectors: clean them and test the resistance for each one. You can pull them and use a 9v battery to produce a click unless it's defective.