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.

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?
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. Has a rough idle with no CEL on

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: Bumping noise when car brakes going downhill

The front brake rotors are warped causing the thumping or the antilock brakes are engaging when they should not be. If the problem is in need of repairs then contact a certified mechanic, such as one from YourMechanic, to inspect...

Q: Door sensor broken

Hi. Yes, the door sensor is connected to the alarm system and will sound the alarm when activated. Have a technician inspect the electrical components as well as the anti theft system for faults before ordering the repair. This may...

Q: Q: A/C blows warm air

Hello. It sounds like you may have a weak compressor. The compressor is a pump for the A/C system and when it gets weak, it does not pump as well as it should. When this happens the air won’t be...

Related articles

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...
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...
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...