Rough idle and sudden drop in power while driving
 

How is it going guys been having a problem with my Cherokee lately and was wondering if someboy might be able to suggest where to look.

When sitting in neutral the idle is fairly rough, but not horrible. It goes up and down, but never low enough to seem like it will stall but still sounds not so good. The real problem is when I am driving. In any gear as I am cruising along it feels for a split second like I lose power and it comes back very quickly, jerking the Jeep a bit. This happens intermittently. Sometimes I barely get it other times it is more pronounced.

Engine temp is good, oil pressure is fine, air filter is a lil dirty but I have had worse, I swapped in a clean one from my buddies rig and it still happened. I did have a vacuum leak before and thought it might be the culprit but I fixed it when I repaired the front end and the problem is ongoing. I am not throwing any codes whatsoever no CEL. The plugs/wires/cap were all done just a year and a half ago so I doubt it is that.

The one thing I was thinking it could be was loss of fuel pressure (probably why it would be more pronounced while under load then when idling). Is there a fairly easy way to test the pump and see?

Wow not a word about what year or even what type of engine you have. You have to give a lil info to get a lil info.

add a sig that says what type of Jeep you have then you never have to worry about adding it.

Also you can add all the info to your profile and then on every post you will get a handy drop down under your avatar that can tell everyone your jeeps info.

Arn't forums great.

Sorry bro I forgot. I kept trying to think of what happens while I am driving I forgot the basics.

4.0 l, 96, Standard transmission.

I would start checking sensors. If you have access to a JY pick up a CPS and TPS and swap them in since they can get a lil pricey at the parts store.

I have a Renix so I have no CEL so I don't know if it would throw a code or not since it may be intermittent.

I don't think it is fuel pressure though.

The rough idle makes me think it's a cat or O2 sensor. Checked to see if you have a clogged cat or bad O2 sensors? An O2 might throw a code, might not, you can never tell with a jeep's electronics.

While cruising might could be a throttle position sensor if you aren't getting any codes. But that shouldn't really affect the idle at all.

Last thought, when my exhaust pipe from the cat to the bad of the truck fell off my wrangler something similar happened because fresh air would hit the O2 sensor and for a second it would buck back 'n pull hard forward.
Just my thoughts, sure someone else has better ideas.

Edit: XJ Stryker posted this at the same time I was writing up, sorry for stealing your idea bro. So..X2 on the sensors.

Holy crap thanks man! Bad connection at TPS got it first try. Now I just need to do my axle U-joint and front oil seal before something else breaks. :icon_lol:

Bad news the rough idle and jerkiness/loss of power came back after I played with the TPS connection. It did finally throw check engine codes it threw these two:

43 and 42 which are:

42 Automatic shutdown relay circuit open or shorted
OR
42 Fuel pump relay control circuit
OR
42 Fuel level unit - no change over miles
OR
42 Z1 voltage missing when autoshutdown circuit energized (The Z1 voltage is the voltage of the circuits fed by the autoshutdown relay. This typically includes fuel pump and switched-battery feed to the ignition coil)
43 Peak primary coil current not achieved with max dwell time
OR
43 Cylinder misfire

Can anyone help me out?

Think I may have the culprit I started pulling plug wires with the engine running to see which cylinder was misfiring/weak and low and behold this happened:

http://i111.photobucket.com/albums/n...G72/wut059.jpg

http://i111.photobucket.com/albums/n...G72/wut060.jpg

Previous owner had given me the receipt for the plugs/wires/cap, so i can't believe how bad that wire was in just a year and a half.

I will be swapping in the new wires and will update when done.

TPS
 

It seems like the TPS

Relax!:walkman:

Same Problem
 

Hello all, I am having the same problem. This thread is giving some direction but my question is how can you check if the CAT is clogged? I did just a visual on the plug wires and the o2 and cat sensors, all looks ok. I have had my check engine light on for two weeks but this problem just started. I figure I will read the codes and start there.

Fixed it
 

I read the codes and got a bank 1 o2 sensor. Replaced the upstream sensor and while I was at it plugs, wires cap / rotor. She runs great!