Skip the auto shop - Our mechanics make house calls

Q: It has a slight rough idle

asked by on

Felt like a misfire, so I replaced plugs and wires. The issue was still there with idle dropping a little low after giving it gas and just a rough in general. Took it to a friend with a scanner because it had a check engine light on and the code was for cylinder #8 misfire. I swapped the coil to the #2 cylinder and then took it back to read but no CEL on. I did a vacuum test and it was at 18in hg and went to 21in hg at 2000 rpm. I took PCM fuse out turned key to start until I heard two chimes and then reinstalled. No CEL on and it drives great but when it's stopped, the idle is slightly rough. It's pretty minor, but it's not smooth like it was before.

My car has 11000 miles.
My car has an automatic transmission.

A: You may have fixed the misfire, but the rou...

You may have fixed the misfire, but the rough idle may be due to clogged injectors and carbon build up on the valves. Try cleaning injectors and throttle body and intake system and see if problem improves. If you the problem still persists, you may want to enlist the help of a certified mechanic, such as one from YourMechanic, to come to your car and inspect the rough idle.

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: Burning smell from under the hood

Hello. A lot goes on under the hood and many of the components can reach high temperatures. Any fluid leaks coming into contact with these hot components can burn the fluids and cause an odor. An example would be a...

Q: High idling on cold start

Hi there thanks for writing in about your 2006 Lincoln Zephyr. This sounds like a failing idle air control valve issue. If this is confirmed, and the valve is replaced, there is also a 'relearning" process for the engine management...

Q: If I change spark plugs and wires do I change the rotor and distributor cap also?

It is recommended to replace distributor cap and rotor at the same time you are having the spark plugs and spark plug wires replaced. The cap and rotor contacts will wear down just like the spark plug electrodes wear down...

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 Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
How to Renew Your Car Registration in Oklahoma(DELETED)
Having your car registered with the Oklahoma Tax Commission is an important part of driving legally in this state. You will need to do this within 30 days of moving to Oklahoma...