Our 99 Ranger is running very sluggish in all gears while driving with the engine cold. Once it is warmed up it does not happen. The spark plugs and wires are new and the air filter is new. What else could be causing this?
One area to check for this problem is the coolant temperture sensor for the computer. If this sensor has failed where it’s telling the computer that the engine coolant temp is at operating temperature on a cold engine, the computer will command the incorrect fuel mixture for the cold engine. This will result in the lack of performance from the engine until it reaches operating temperature.