My Toyota Tacoma had been experiencing this problem for three years now. When I'm stopped at a light the vehicles rpm's fluctuate between normal and dropping with a bit of shaking, and to the point where it stalls with no check engine light. I have had a many spark plugs replaced, 3 step fuel system cleaning and even replaced the IAC last year, but to know a avail. I was wondering if this could be a TPS problem or a fuel filter problem, or even something else?
My car has 194543 miles.
My car has an automatic transmission.
This may be a sign of a faulty MAP sensor. The Manifold Absolute Pressure (MAP) sensor senses engine load and generates a signal that is proportional to the amount of vacuum in the intake manifold. The engine computer then uses this information to adjust ignition timing and fuel enrichment. When the engine is working hard, intake vacuum drops as the throttle opens wide. The engine takes in more air, which requires more fuel to keep the air/fuel ratio in balance. When the computer reads a heavy load signal from the MAP sensor, it adjusts the fuel mixture to slightly more rich than normal so the engine can produce more power. The computer will then retard (back off) ignition timing slightly to prevent detonation (spark knock) that can damage the engine and decrease performance. This may also be caused by other closely related components such as a dirty or failing mass air-flow sensor, a faulty throttle position sensor or potentially a vacuum leak. I would recommend having an expert from YourMechanic come to your location to diagnose and replace your MAP sensor.
Have a car question? Get free advice from our top-rated mechanics.