Q: Seems to be an occasional misfire that is somehow related to the AC compressor

asked by on

If the AC is off when I start the car, I have no problems. Sometimes right after starting the car if I switch the compressor on it will cause the car to run rough for a bit and then it just stalls, but will start up again without a hitch, maybe running rough for a hundred feet or so. I have recently replaced the compressor myself and it has been in working order for several weeks. If the AC is not on the typically I do not have this problem. The problem feels like a misfire but the odd part is that it is related to whether the AC is on or not. Other than that the car runs great. With the AC on when the car has been running for a while it does not kill it but rather causes it to idle a bit rough. Any advice would be wonderful. Also if there is a way to diagnose a coil pack without going to a shop this would be wonderful. I have some tools but not all the fancy ones. Thank you in advance! -Alex

My car has 171000 miles.
My car has an automatic transmission.

This is normal when the AC is on. The air conditioning compressor requires torque from the belt system on the engine to power it. When the AC is off, the compressor clutch does not activate, meaning the AC is not straining the engine. When the AC is on, the compressor clutch activates, causing the drive belt on the engine to turn the compressor. The Idle Control Actuator is what controls the engine idle. When the AC kicks in, the engine will drop some RPM, and the actuator opens to allow more air into the engine. When you are at speed, the throttle is open from the accelerator pedal under your foot. the Idle control actuator is not active at this time. What you describe is normal.

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
  1. Home
  2. Questions
  3. Seems to be an occasional misfire that is somehow related to the AC compressor

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: My truck has a knocking noise from a bad lifter

A bad lifter will not make a knocking noise. It will make a tapping noise. I would recommend having a qualified mechanic listen to the noise to see if it is a lifter noise, a piston rod, or main bearing...

Q: Air compressors and air suspension fail

This is a common fault that is found with vehicles that have air suspension. Though the compressors were most likely bad the first time, there is another problem causing them to fail. The most common would be a leak in...

Q: 2002 Chevy cavalier. The RPMs are jumping when stopped then AC blows cold till I slow down or stop then it blows warm.

What you are describing sounds like a dirty or failing idle air control valve. The idle air control valve monitors the air intake as it is mixed with fuel prior to being injected into the engine at low speeds and...

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...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...