Please Help...Extra Rough Idle

My 89xj 4.0 is idling so rough you would think it was a major vacum leak. I have not found one. I have replaced the map sensor, idler motor, and the spark plugs. Still idles so rough that the motor shakes and sometimes stalls. At 1500+rpm the engine smooths out pretty good. Has anybody got an idea what this could be. I am out of money and ideas. Someone told me it is the O2 sensor so I unpluged it with the engine running and no difference plugged or unplugged. Please Please Help. I have to take a 200 mile trip on Sunday.

Okay here's a couple of cheap things that might help:

1. Grab a can of throdle body cleaner and clean it. See if you can't get some down there in the intake manifold as well. Should cost you about 3 bucks for a nice big can. I removed stepper motor and cleaned it up and removed TPS just because those things are so tempermental about any kind of liquid getting anywhere near them...

2. Remove the brake booster vac line and with the engine running, slowly allow some fuel injector cleaner to be sucked down into the intake manifold through the hose. About another 3 bucks. Also, while you're at it, dump a bottle in the gas tank. Might help a little if your injectors are getting clogged up.

I solved a whole host of problems with my 88 just cleaning out the crap in the TB. The fuel injector stuff might have helped or might have done nothing... I really don't know. :greensmok

After cleaning the TB, check your cap and rotor plugs, wires then your o2 sensor ect.. Sounds like all ya needs is a tune up.

Here is a list of items that affected the idle of my 88 XJ, 4.0 AW4, all seemed to contribute, every one seemed to have a helpful benefit. Listed in the order I found and fixed them.
Plugs, changed from Bosch to Champs
Distributor cap
number 2 spark plug wire high resitance
Replaced all the cables, because the boots were hard and cracked
Air filter, went to a oil and cloth filter, mainly because if the paper filter gets covered in oil (happens) it passes very little air. Not because of flow benefits or HP gains. Really helped
Fuel injector cleaner
Worn drive gears in the distributor
Worn spacer between gears and shround
Cleaned all grounds, really helped
Another load of injector cleaner, really helped
Plugged the vacume line where it connects to, the EGR valve (gonna get a new EGR sometime) The springs were weak and the EGR was opening too soon, also may have been a slight diaphram leak, seemed to help the idle some. Made the motor stumble some until it got above 1000-1500 or so.
Replaced cat and muffler, the old cat was still good (found after removal), the muffler was partialy (mostly) plugged
Adjusted TPS, really helped
Unpluged and plugged, many and varied connectors, the rubbing of a little in and out action, often helps with contact.
Still to do list
fix the broken stud on my intake
New intake gaskets
intake and throttle body cleaning
wiring to the 02 sensor, temp. sensor and knock sensor is fairly cooked, found a junk yard harness.

Along with a smoother idle, my gas mileage has been going up, up up :loveu: along with power.

EGR?

Unplug the vaccuum hose going into the EGR and plug it with a small bolt...see if that changes the idle....

A bad egr that does not fully close at idle can cause very rough idle and engine dieing at idle. If crud gets on the valve and prevents it from closing even the plug the vacum line test will not help IIRC since crude could keep it from closing. Remove the valve and blow on the exhaust gase inlet port to see if the valve provides a good seal closed. Greg

Did you make the trip?