Mitsubishi Repair: 1991 2.4 cold start problem, coolant temperature sensor, mass air flow sensor

Question
Anthony,

I own a 1991 d50 pick up with a FI 2.4 mitsubishi motor.  Has a major cold start problem.  Funny thing is once its started it runs great and will start right up all day long.  The dealership I recently bought it from had the idle up real high.  When I turned it down the cold start problem got worse. Hope you can guide me to the problem.

Answer
Marc,
This is most likely a problem with the throttle body, Idle Air Controller (IAC), engine coolant temperature sensor, base idle setting screw, EGR value, or throttle position sensor.  I believe your engine also has a Fast Idle Air Valve (FIAV).  This value mounted below the throttle body is only supposed to be affective when the engine is cold to allow hot air to warm up the coolant.  If this valve does not close once warm, it can cause rough idle.  Also, the mass air flow sensor should also be checked to be sure the sensors are funcitoning properly.

If this does not turn out to be an air intake problem, it could be a fuel problem.  Your fuel injectors may be leaking fuel into the cylinders and causing a flooding issue when left to sit overnight.  Once your engine warms up, the excess fuel burns off and runs and starts properly.  It would also be a good idea to have your battery and starter motor load tested just be sure.
Good luck!