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I have a 1990 2.9L V6 Ford Ranger (Mazda engine). The truck dies at a stand still when engaged in Drive or Reverse. The tachometer drops to 500 rpm's and the voltage meter goes down. The problem is worse when the lights are on! When in Park or Neutral the rpm maintains @ 750 and the truck runs fine. The battery has been replaced, the alternator tested fine and all grounding contacts have been sanded and cleaned. Could this be the throttle position sensor or the transmission speed sensor?

From MY experience I will say the biggest problem is a very dirty plenum chamber and/or throttle body. Most of these models have a little sticker on the throttle body that tells you NOT to clean the throttle body. Since the early 90's they have come out with throttle body cleaners that WILL NOT hurt the Teflon coating on the throttle body. (DO NOT USE CARBURETOR CLEANER OR THIS "MAY" DESTROY THE TEFLON COATING!) Here is the procedure I would like for you to try. 1) Remove air snorkel from Mass Air flow sensor to throttle body. 2) With the engine off and keys out of the ignition have someone hold the gas pedal to the floor. (You can put a brick on the gas pedal to do the same thing) 3) Take the aerosol can of throttle body cleaner and a rag and clean the "butterfly" or throttle plate and the surrounding area. (Do not use a tooth brush, use only a soft rag) 4) After you have cleaned the throttle body well, remove the "Curb Idle Motor" which is attached to the side of the throttle body. You will need an 8MM socket to remove the "Curb Idle Motor" 5) Use the throttle body cleaner to clean the "Curb Idle Motor" of all carbon and dirt you see inside the two orifices. 6) Re-install the "Curb Idle Motor" and the air snorkel then start your truck! If I am correct about this problem you truck will perform flawlessly from this point. If it runs better and only dies ever so often, then replace the "Curb Idle Motor". This is something I tell people they need to clean every other oil change as PREVENTIVE MAINTENANCE! The idle speed is controlled by the computer at the "curb idle motor." If it is dirty and sticky it will not respond to the commands from the computer. The throttle plate and Curb Idle Motor work together to maintain proper idle when you put a load on the engine. Such as turning on your lights or putting the truck in gear.


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