Toyota mr2

i have a 91 toyota mr2 that i hadn’t driven in a few years. when i decided to use it again i had a major tune up done, a fuel pump, filter and strainer installed, timing belt, water pump, assorted gaskets, pulleys, and seals and an air idle control valve. after i drive the car a short distance and then stop for a light or something else, the motor revs and then slows down repeatedly on its own, but it never stalls. if i tap the gas pedal it sometimes will stop doing this for a while. toyota suggests it could be the throttle control switch. help…

Check your coolant. I’ve got a 93, and the coolant is a huge pain in the rear on those cars, because the radiator is up front, but the engine is in the middle. So there’s two very long coolant lines that go under the car and then up to the engine. That makes bleeding the coolant very time consuming and troublesome. The bleeder valve is located in the engine bay. You cannot bleed the coolant by using the radiator cap like you can with a normal car.

That’s probably where the mechanic who tuned it up screwed up. He bled it off the radiator, leaving a large airspace in the top of the system, which is in the back. So now you have air bubbles running through the system, and when they hit the coolant temperature sensor, it registers a drop in temperature. The engine then goes into cold-loop mode, which means it dumps more fuel in order to run rich for warmup. That makes the engine rev. Then the bubble passes and coolant hits the sensor again, so now the computer thinks the engine’s warm and cuts the fuel mix, and the engine revs down again.

Don’t forget to flip the heater on when you bleed - there’s a lot of coolant in the heater core and its lines.