Skip the auto shop - Our mechanics make house calls

Q: Has a rough idle with no CEL on

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 111000 miles.
My car has an automatic transmission.

A: I would try and have the fuel injectors and...

I would try and have the fuel injectors and throttle body cleaned out. This should clean out injectors and intake valve carbon deposits that can cause the rough idle. If after driving the vehicle, and the CEL comes on, then have a mechanic diagnose the rough idle and do not disconnect or reset PCM unless directed to by a pinpoint test. This just puts the PCM in factory setting and may take a few weeks for it to see a problem again.

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: I replaced pcm and now I'm getting code u0100 and p0700. Battery is new and not holding enough bolts. Something is draining it. Wh

To determine if the cause of those two codes is low voltage, I would simply fix the parasitic power draw first, reset the PCM (erase the codes) and see if the problem recurs. The cost to resolve such an electrical...

Q: I need a alternator my Vin is 1GCGK23U44F245647 could you tell me if I need a 105 or 145 amp

Assuming the alternator is original, and thus has never been replaced or substituted with a part that is non-original, you can quickly tell which one you have by reading the tag on the alternator. You will see a tag that...

Q: Rough idling, check engine light on

First have an experienced technician, like one from YourMechanic, look the vehicle over and read the fault codes from the vehicle. The trouble code may unveil a problem causing the rough idle. Otherwise make sure the maintenance has been kept...

Related articles

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...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.