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.

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

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

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: Engine

The running rough may have something to do with the two different years of the engines but only a computer scan and fuel pressure test would be able tell. Have a certified mechanic, like one from YourMechanic, diagnose the car's...

Q: Can a faulty sensor keep the engine from starting?

Today's automobiles use many different sensors to signal engine controls and computer circuits to start a vehicle's engine and run all the programing for fuel, timing, and emissions control. Bearing this in mind, it is critical for the vehicle's main...

Q: What does it mean when my batteries server active light reads on the car and what should I do it would not crank up?

You can do a couple things, you can connect a battery charger and charge the battery or you can jump start it with a jumper box or jumper cables. This light indicates the BCM (body control module) has detected the...

Related articles

How Do Power Car Windows Increase Passenger Safety?
Power windows are responsible for approximately 2,000 emergency room visits every year. When a power window closes, it exerts enough force to bruise or break bones, crush fingers, or restrict an airway. Though...
How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the...