Ok winter is here and this **** would happen now! I have a 98 xj 4.0. So here is what's been happening, I start it up and start driving down the street and then it has no power, rpms jump around and boggs down but stays running! It backfires sometime too to me it seems like it is in the intake. Sometimes when its parked the idle it does the same thing sounds like its going to die and then jumps up and back down. I have replaced the idle control valve, coolent temp sensor, and downstream o2. Upstream o2 is only like a year old. I did have the cat cut out a few weeks ago and installed a straight pipe. I know the upstream o2 is saying ritch from a code reader from the shop down the street.

Please winter is here for me and I want it running in top shape, so any info would help! I am kinda new to all this stuff so I am still learning.

When was the last time you did a tune up? (cap, rotor, plugs wires) cps? Tps? Map? All candidates that could contribute

sounds like a malfunctioning throttle position sensor issue - it's one of the things that controls timing and fuel.

Test it first before replacing:




TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (SEE Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

Or the map sensor.

map sensor only affects engine operation in open loop mode before the engine/o2 sensor warm up, and above 80% WOT. It does not affect anything at idle or moderate acceleration once the engine switches to closed loop mode.

Ok so I have replaced the map, up and down o2, idle control valve, temp sensor still the same problems! Thinking Tps and maybe injectors next!

This looks like the diagram for testing the cps! Am I wrong?

Definitely do the tps. Sounds like the root cause of your rough idle

Changed the tps with just another one didnt do anything! the rough idle is all the time but it gets worse after running for like 10 min after start up. its running rich as hell too!

get some electrical cleaner in the can and clean all those plugs on the inside i did it
also you could take your throttle body off and clean that really good with a toothbrush and some dish soap