Rpm increasing when engaging clutch



izusu trooper '99 w/137K miles. just started that only when engine cold in the a.m. after engaging the clutch the rpm’s go really high and the car seems to accelerate slightly. this goes away after 15 minutes or so of driving on traffic. what could be the reason?


The problem might be with a defective coolant temp sensor.

When the engine is started cold, one of the primary inputs to the computer is the coolant temp sensor. Depending how cold the coolant is, dictates how fast the engine will idle when started. As the coolant heats up the idle speed decreases.

Sometimes these sensors become lazy to where they don’t react pricisely to the coolant temp. And this can result in the fast idle remaining long after the coolant is up to operating temperature.