Skip the auto shop - Our mechanics make house calls

Q: Rough idle at stops lights and when parked

asked by on

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.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. Rough idle at stops lights and when parked

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Heater broken

Hi there. This is a common problem with the specific vehicle you have. The AC and heater are separate from each other. However, your vehicle is infamous for having a leak in the heater core causing the air not to...

Q: Engine revving high at idle - 2013 Infiniti JX35

Hello. You may have to have the computer reprogrammed for the idle to come down. There is a technical bulletin to reprogram the ECM or replace it if needed. Take the vehicle to the dealer to have the reprogramming done....

Q: I have a crack on my windshield

Every state will vary as well as the person performing the inspection. However, in most states, a crack larger than 4 inches will not pass this kind of safety inspection. There are also different types of cracks that have different...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.