Q: Rough idle and RPM fluctuation

asked by on December 17, 2016

So here is my issue I was on my way home last night and the roads were slick and I was sliding quite a bit and all of assuden my truck started to want to die and at every stop sign I would have to restart my truck when it does idle it idled at like 500rpms sometimes lower and when you let off the gas while driving or just in park it will dies most of the time I hooked it up to a code reader and the only code I found was an issue with the map sensor so I replaced the map sensor but I'm still having the issue

My car has 185000 miles.
My car has an automatic transmission.

Hi There, As you may know, 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 computer reads a heavy load signal from the [MAP sensor]((https://www.yourmechanic.com/services/manifold-absolute-pressure-sensor-map-sensor-replacement), 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.

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

2005 Chrysler 300c has a code P0406. I believe EGR needs replacing, Don't know if it will make it 25 miles to dealer.

P0406 involves the EGR system but that may or may not be the only factor causing your rough running condition. Typically, P0406 will set if you have a failed EGR valve, excessive carbon buildup, an open or short in the...

2009 Dodge Journey check engine light blinking

Your engine is misfiring. When the check engine light starts blinking, that means the misfire is severe enough to damage the catalytic converter. As for the ABS light coming on when you hit a bump, that's probably due to loose...

Car brakes are stuck on.

Try putting the transmission shifter in park or neutral and see if the brake pedal becomes unstuck. If not, then you may have to remove the battery cables to reset the electrical system so that the parking assist is shut...

Related articles

The Best Used Cars to Buy If You're Towing a Boat
If If you’re towing a boat, the vehicle that you buy is largely going to depend on the size and weight of your boat plus trailer. Most cars, realistically, aren’t cut out for the job. We recommend a pickup truck...
The Best Used Cars to Buy If You're a General Contractor
If If you're a general contractor, you probably aren’t in the market for a used car. More likely, you’re looking for a pickup truck, because you need to haul equipment and supplies to various job sites. Most contractors will likely...
2011 Dodge Ram vs. 2011 Ford F-150: Which One Should I Buy?
Large trucks can be fun to drive, and even more fun to get dirty. Unfortunately, they may also cause you to get phone calls from friends who need to move into a new apartment. Fortunately, just having a truck may...