Skip the auto shop - Our mechanics make house calls

Q: Car is idling rough and missing

asked by on

My car is missing ,really bad, thought catilac converter was stop up the way it sounded and ran... It wasn't, so put new coil packs,spark plugs and wires on it still didn't help.. It spitting sputtering and has black soot coming out of tail pipes,and black smoke.. Has about all new sensors except for throttle position and map sensor, please help me on what it could be.. Thank you...

My car has 200000 miles.
My car has an automatic transmission.

A: This may be a sign of a faulty MAP sensor. ...

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

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: No power, car sounds very rough.

The first place to start when trying to diagnose a vehicle with running issues is to have it scanned for diagnostic troubleshooting codes. This will tell you if any sensors have detected any issues, and may give you some more...

Q: Check Engine Light control board balancer

Hello. The balancer is the main cause of this on your engine. They fail all of the time and need to be replaced. Depending on the age of the engine, you can simply fix the balancer issue, but if the...

Q: Car stalling while driving - 2006 Pontiac Grand Prix

Hi there. The P0033 OBD-II error code is a generic code that typically indicates a problem with the Turbocharger or Supercharger Bypass Valve Control Circuit. In most cases, the reason the code is triggered is due to a vacuum...

Related articles

What are the Car Pool Rules in Hawaii?
Hawaii is widely regarded as a land of vacation and relaxation, and as such, its scenic roads and routes are far better known than the state’s freeways. But, as with all...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
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.