Q: Rough idle at stops lights and when parked

asked by on November 12, 2016

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?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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

Hard shifting, worse with lower gears

There should be no need for you to have to replace your transmission yet. You should get a full diagnostic check from YourMechanic first before any part or component replacement. The problem you describe can be caused by a few...

Second time on same wheel 4 or more of 6 lug nuts snapped off while driving

The problem may not be the hub or studs, but the rim. Look at the inside of the rim-centering hub to see if it has damage where it has not been seated properly or is unable to be seated. If...

the car revs high and at stop signs while slowing down then idles down suddenly and sometimes stalls, whats the cause?

The engine intake manifold seals or the intake tubes between the mass air flow sensor and the throttle body may have a leak that you cannot hear, but could be found using a smoke machine designed to find the leaks....

Related articles

10 Best Stores to Buy Auto Parts in Tacoma, Washington
Automotive technicians rely on auto parts stores to add and replace car parts. The best auto parts shop in Tacoma is O’Reilly Auto Parts.
How to Get Toyota Dealership Certified
Toyota car dealerships offer automotive technician jobs to mechanics who are certified through the Toyota Professional Automotive Technician program.
Toyota Certified Pre-Owned (CPO) Car Program
If If you have been shopping for a used Toyota vehicle, you may want to check out cars under their certified pre-owned program. Many manufacturers have a certified pre-owned (CPO) program, and each one is set up differently. Read on...