As I stated in another post quoted below, 87 octane did not cause the car to have a run problem nor will it have caused any damage. Modern cars will reduce ignition timing to compensate for the lower octane.

The short story is take it to a competent shop and let them fix it, you will just be guessing and randomly changing parts.

https://www.peachparts.com/shopforum/tech-help/396561-2003-c320-running-rough.html

Old 12-19-2018, 07:34 PM
97 SL320
Registered User

Join Date: Jan 2012
Posts: 7,028

97 SL320 is online now

Better buy her something good for Christmas, regular fuel won't cause a rough idle. About all that will happen is a slight reduction of max power due to ignition timing reduction. At part throttle you won't likely notice a difference.