1993 Jeep Cherokee

Hi albertsneijMD. Welcome to the forum. It could be a wire rubbed through and shorting to the body or some other piece of metal, but more than likely it is just the speed control servo unit that has a break in one of the solenoids. The Engine Computer will disable the cruise control system because the affected solenoid could be the "Dump" valve which kicks it off when you press the brake pedal. It's a safety thing that's programmed in.

To find the servo, (I can't remember where it is on your vehicle), follow the two throttle cables back from the throttle body on the engine. One will go to the firewall to the gas pedal. "That ain't it". Follow the other cable to the servo. The servo will have a four-wire plug.

I autopsied a servo that I replaced under warranty and found a corroded spot where the wire had come loose. Resoldered it and it worked fine. In the 15 years since, I've only run into one malfunctioning servo. My reason for mentioning this is to show how little problems they normally cause. For that reason, I would have no worries about sending you to a salvage yard for a used one. If your vehicle uses the newer small black servo that does not use a speedometer cable, it should be the same part that is used on all Chrysler vehicles throughout the 1990s.

Before you go looking for a replacement, check the electrical connector for signs of corrosion. You can also perform resistance measurements to verify there is a problem in the servo itself. If I can dig up a service manual, I can tell you which pins to measure. If the servo test ok, you can perform the same measurements at the Engine Computer's connector. That will test the wiring AND the servo at the same time.

caradiodoc

I gave you inaccurate information the first time
jeep 1993 cherokee , Liberty 4.0 automatic.
after I took my car for a leaking water pump , which was replaced, my car died after 2 minutes of driving.
the mechanic said that the spark senor was to be replaced. he replaced it but left a red light" check engine" . he said that the computer was bad and needed tp be replaced.
I did not trust him.
I drove the car for a while but it stalls some times.
the code is 34.
I do not know what to do.

Does the cruise control work? There was no Liberty in 1993 so either the year or model is wrong. Regardless, the codes should be the same. Does the engine stall while driving or just when coming to a stop? Does it restart right away? Will it stay running if you hold the gas pedal down a little? If so, the battery might have been disconnected and the Engine Computer has to relearn "minimum throttle". To do that, drive at highway speed with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals.

If the stalling occurs while driving at a steady speed, and / or you have to wait for the engine to cool down for a half hour or so before it will start and run again, suspect a failing crankshaft position sensor or camshaft position sensor. Normally they will set a fault code but sometimes the engine stops rotating too quickly for the computer to detect the missing signal.

caradiodoc

the car stalled the first time on the highway, it took several cranks to start. the smoke comes out dark.
it was noticeable that that car stalls after a stop and take off again. as far as the cruise control work, should I try it on the road ?
once I start the car after long rest, the car runs ,for ever, while parked even if I press the gas peddle to any degree. no problem.

You have a fault code related to the cruise control. If the cruise control works, the code was read wrong or the problem is intermittent. If it was read wrong, the proper code is an important clue to finding the stalling problem.

If the engine only stalls when coming to a stop sign and your foot is off the gas pedal, the Engine Computer may just need to relearn "minimum throttle". To do that, drive at highway speeds with the engine warmed up, then coast for at least seven seconds without touching the brake or gas pedals. Once the relearn takes place, the computer will know when it must be in control of idle speed.

caradiodoc