Last attempt before dealer!

So my 93 xj 4.0 auto with 144k miles has the following weird issues ;
Bumpy idling- rpms are fine they don't fluctuate. It's just bumpy.
On drive, when at 35 mph steady, rpms go up and down.
On drive at 55-60 it bucks- rpms stay the same
On drive at stop- it bucks rpms go up and down and at times it dies
When backing away from parking spot- R to N to D and it stumbles when placed on D
At times when it's bucking at stop, if I put it in N it's ok. Change it to D and dies. Catch it before it's going to die place it on N and it revs to stay alive.

This is what I've done to it
New CPS dealer and Vatozone (dealer mounted now)- wires-plugs-distributor and cap- injectors- fuel filter- fuel pump- fuel regulator- ECU- IAC-TPS-o2 sensor- Cat converter- cat man (was cracked)- coolr temp sensor

I'm over this!!!!!! I already spent what I paid for it!!!

Any compression testing?

Check fuel pressure at fuel rail

Haven't done compression
Fuel pressure is up to the book. When it hesitates and bucks- fuel pressure doesn't change.

Laurent Wagoneer said:

Haven't done compression
Fuel pressure is up to the book. When it hesitates and bucks- fuel pressure doesn't change.

Click to expand...

Gotcha. Is your throttle body clean inside?

Yep. Cleaned the whole intake manifold when installed the exhaust manifold.

how did the plugs look? how do the new ones look. plug readings tell quite a bit. have you checked your electrical system? grounds especially. what shape is the battery in, holding a good charge? what does the spark look like? have you checked the coil? and go take a compression check. a leak down if you have the tools to do so. AIR/FUEL/COMPRESSION/IGNITION are the basics for an engine to run. when one gets compromised you track it down. it can be very frustrating i know, but keep trying. you will get it. good luck.

Did u gap the plugs properly?

Did you scan for codes? Just wondering.

Could be an electrical short somewhere - sounds like engine torque is causing a bare
wire to ground out on something. Check the fuel injector wire harness for chafing or
worn insulation - especially in the area of the end of the fuel rail (ask me how I know
this). Check the wire harness that leads to the starter. Check the O2 wire harness as
it located near to the exhaust manifold. Don't just look at the wire harnesses; use a
flashlight and run your fingers along the harnesses as any worn spots will be probably
be facing away from you.

You need air, fuel, compression and spark. A motor won't run without adequate compression. If your valves or rings are shot, you are just wasting time and money. Also risking putting new bad parts on, which can really mess you up. Test until you find something wrong before changing more parts.

Variations in idle can be caused by a vacuum leak. Many times an intake leak or the gasket under the throttle body is to blame. Use some carb cleaner to diagnose. Spray around the TB base and around where the intake mounts to the head. Take a pair of vice grips and clamp off the vacuum line to the brake booster.

I had a cracked vacuum line to the map sensor that caused bucking on my renix.