idle problems

[odjeep]

My buddy has a '99 cherokee with the 4.0 and the aux engine fan wont shut off. It stayed on for like 20 min after shut down before we intervened.
I unhooked the fan to shut it off. Could this be a thermostat sensor or something? Also it is having a hard time idling. Think maybe a fuel problem. What do you guys think?

od

[XJNick]

Hi,

The fan relay is most likely stuck on. You can tap it lightly with a hammer as a temporary fix, but it'll get stuck again. I'm not sure where the relay is on the '99 models.

As for Idleing problems, the first thing you should do is clean the Throttle Body and Idle Air Control (IAC) motor passageways with carb cleaner. If that doesn't fix it, test the Throttle Position Sensor (TPS) for proper operation, and be sure you have no vacuum leaks.

-Nick

	Throttle position sensor A throttle position sensor (TPS) is a sensor used to monitor the position of the throttle in an internal combustion engine. The sensor is usually located on the butterfly spindle so that it can directly monitor the position of the butterfly throttle valve. The sensor is usually a potentiometer and therefore provides a variable resistance dependent upon the position of the butterfly valve (and hence throttle position). The sensor signal is used by the Engine Control Unit (ECU) as an input to its control system. The ignition timing and fuel injection timing (and potentially other parameters) are altered depending upon the position of the throttle, and also depending on the rate of change of that position. For example, in fuel injected engines, in order to avoid stalling, extra fuel may be injected if the throttle is opened rapidly (mimicking the accelerator pump of carburetor systems).