Skip the auto shop - Our mechanics make house calls

Q: Rough idle at 500 rpms

asked by on

Replaced #7 coil and spark plug after plugging in computer. Did not fix. Engine runs smooth while driving. 105,000 miles

My car has 105000 miles.
My car has an automatic transmission.

A: The first thing to do is a cylinder balance...

The first thing to do is a cylinder balance test to see if all cylinders pass this test and relative compression test. If a cylinder fails either test, then follow the pinpoint test and see if the injector is getting signal using a noid light. Check the injector for proper resistance. Swap the #7 injector with another cylinder injector or with a known good one and see if this fixes the problem. If you swapped to another cylinder, then the code will move from #7 to the cylinder you swapped the injector with. Replace the injector and clean all injectors using a pressure type injector cleaner. If you want to have this inspected in person, a technician from YourMechanic can come to your home or office to diagnose your car's rough idling issue.

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・Save up to 30%

Get a quote

What others are asking

Q: Truck is broken.

Unfortunately with such limited information on your 1969 Ford truck, it would be extremely difficult for me to guide you in the right direction. Having good information for a technician to help you is key in times like these. The...

Q: Lots and lots of trans issues, probably a lemon

Ford has issued multiple Technical Service Bulletins (TSB) in last few months pertaining to transmission shuttering, slipping, and leaking shaft seals. I would suggest you set up an appointment with your dealer to have the transmission module reprogrammed. Also check...

Q: Car filling up with water when it rains

Depending on where the water is located you could have a leak in a weatherstrip seal on a door or trunk, a windshield, or the rear glass. There are instances where the weather stripping on the body panels fail. There...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
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 P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...