My 89 4.0 has me stumped!

89 XJ 2DR 4.0 5sp. 2WD Sport...Engine stumbles above 2K RPM OR shakes at idle. I've checked grounds and connections and verified sensor's readings and operations. Has about 130K miles on it but can't find the problem!

I would start with the basics; sparkplugs and wires,
distributor cap and rotor. If you have a multimeter, you
can do resistance and continuity tests before buying
new parts. Plugs will have about 5-7K ohms and wires
will have about 10-12K ohms (per foot).

Also try cleaning the throttle body. Carbon tends to
build up where the throttle plate meets the housing.

If that doesn't help check for vaccume leaks and the o2 sensors. Atleast the upstream one


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Just a wild guess is the catalytic converter clogged?


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Best guess would be O2 sensor. But before you spend the bucks, check for weak spark.

Open an old plug up to sixty thousandths, look and listen to the spark. Sharp blue white spark that makes a crack sound is good. Fat yellow spark that splashes isn't good.

Make sure you ground the plug well, wear rubber gloves and don't rest your crotch against the fender when visually checking spark.

You can also read a plug when you remove it. Two ways to read it, at idle and after a few minutes of running a hot motor at 2000 RPM.

Various reason for weak spark. Most common is the plug and coil cables. The ignition module and the coil separate, the connector gets corroded and/or loose. Also possible to get low voltage into the ignition module, dirty connectors between the module and the ignition switch or an issue at the ignition switch itself, the switch or the connector. The ignition switch connector has a tendency to melt down.

The distributor cap has a tendency to cross fire, the spark jumps to the wrong plug pole inside the cap. Can be from excessive wear between the poles and the rotor, carbon dust from the center rotor pole wearing or moisture inside the distributor.

A lesser chance you are getting flaky readings from the TPS, TPS has a lot to do with the timing. MAP vacuum issues, also has timing input and a lot to do with fuel mixture.

A good way to chase down a single or multiple cylinder miss is use a timing light on one cylinder at a time, watch the light against a dark background like the relay block cover, you can see a miss on that cylinder. About the only use for a timing light on a Renix, besides verifying that it does indeed advance.

Check the O2 and knock sensor harness where it runs up the front of the motor, it can rub through or melt in almost impossible to see spots. I had to disconnect mine and pull the harness up far enough to see the burn spot. Cruiser has a write up on how to route that harness to avoid that issue.

Good luck.

Thanks guys! Plugs and wires are A1 condition and new MAP and TPS made no change. I'll check cap and O2/knock harness and sensor.

Can the famous renix ground problem cause this issue?


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I think the spark plug wires are 1000 ohms per foot. At least the ones I buy are.

Runnin'OnEmpty said:

I would start with the basics; sparkplugs and wires,
distributor cap and rotor. If you have a multimeter, you
can do resistance and continuity tests before buying
new parts. Plugs will have about 5-7K ohms and wires
will have about 10-12K ohms (per foot).

Also try cleaning the throttle body. Carbon tends to
build up where the throttle plate meets the housing.

Click to expand...

b5blue said:

Thanks guys! Plugs and wires are A1 condition and new MAP and TPS made no change. I'll check cap and O2/knock harness and sensor.

Click to expand...

What all have you already done. A list would be real nice.

Check that you did not criss cross 2 plug wires when you replaced them. Then pull one plug wire at a time from the cap and see if the engine runs worse (it should). If there is no change that is a dead cylinder and you need to find out why. Compression, spark plug, SP wire, cap-rotor, fuel injector or its wiring.

Even a new plug or wire could be bad. Make sure all the plug wires are securely attached.

When did the problem start. Was any work done before it started?

Disconnect the O2 sensor and see if the problem goes away.

Check the sensor grounds from the battery negative post to the sensor grounds, O2 and MAP for sure.

Check for arcing in the SP wires at night in the dark just to be sure the wires are good.

Does it ever run smooth, if so when, or just rough at idle and all the way to 2000 rpm? Your OR comment does not tell us enough. What does it during decleration, acceleration and at various fixed RPMs.

Have you checked the fuel pressure, and be sure to check the FPR vacuum nipple and vac hose for signs of gasoline. If you find any the FPR is leaking gas directly into the intake, bypassing the injectors. I assume you checked both ends of the MAP sensor vacuum hose since it is a new MAP sensor?


If you find 1 or 2 bad cylinders (after checking the plugs, wires and maybe the injectors), you need to do a compression test next. Compression test on the ???able cylinder might make more sense before pulling the fuel injectors? Your choice....Might be a bad injector...

You may have more than one problem.

Have the injector connectors been disconnected at all? If yes, make sure they are back on the correct injector, and making good contact. I found one after years of issues that has a sweet spot, gets a loose sometimes LOL. The spark plug wire test above will tell you if you need to check each injector/wire/wire connector next, or not.

Only time I ever had a really rough idle was a blown head gasket between two cylinders or when I pulled a plug wire or Injector connection to kill test a cylinder. Never had a sensor problem on my renix cause a rough engine shake. I know an O2 sensor can cause it shakes when giving it gas, or when the heater in the sensor goes bad as the sensor cools at idle, but it is not an always rough idle in park!!!!!

Bad Cat should not cause a rough idle, if it does it is bad enough to kill the engine at 2000 rpm, as in almost totally blocked.

Thanks for the reply Mike. I'm going to do a few things suggested and report back. Basically the thing was running fine for quite a long time as I'd done all the things you guys recommended! (Back when first bought.)

One thing you can do is figure out if the miss is on a cold motor or a hot motor.

Could be something really simple, been through any mud puddles lately?

2000 RPM bucking for me has always turned out to be something with the O2 sensor, either the sensor itself and oil soaked sensor/connector or the harness.

A weak CPS signal can also cause issues, the first sign is usually hard starts.

I've had a miss at idle multiple times for multiple reasons.

Mike may be right about you having multiple issues.

Push sideways on your distributor shaft/rotor. Up and down movement has never caused me any issues, but sideways movement of the shaft has.

Thanks again guys...

so its running good now? what fixed it?