2006 Buick Terraza Q&A
2006 Buick Terraza Question: Slight rough idle. RPMs fluctuate 150± sometimes. Surges at highway speeds.
Vehicle has 121,000 miles on it. Local Oil change service company said CAM timing sensors were bad. No codes on then or now. They just thought that would be the fault. Took it to Buick dealer and replaced plugs and wires and ran BG fuel treatment through sytem. Did not replace CAM sensors. Surge going down interstate is only slight, like moving gas pedal back and forth. Rough idle is very slight at stops but can vary in degree. Dealer drove vehicle with computer attached and found nothing. They said one time while idling in shop, engine stumbled slightly but not enough for computer to register it as an engine misfire. Technician thought it may be slight injector misspray on cylinder 5. Put full tank of premium gas and some Sea Foam in (1 oz per gallon). Been running this for a week now and no improvement. I suspect a bad Oxygen sensor or possibly fuel injector. I haven't replaced fuel filter in a while but it doesn't seem to be a fuel supply problem. Not sure if Dealer checked fuel pressure. If there is a vacuum leak I haven't found one unless it is very small. Sitting at idle, the RPMs fluctuate slightly maybe 100 to 200 RPMs on the tachometer. - longtime GM user
This could be so many things. How are your mode 6 readings? This is the scientific data for the OBD-II system, not just scan data. See if something is borderline, like fuel trim, misfire counts, EGR ( if equipped ) and yes air/vacuum leaks. How are your coils? And how old is the mass air flow sensor? Again, check your fuel long term fuel trim, It needed to be no more than 4-5% on either bank. - dandd