2007 S-Type V-8

I have an intermittent engine vibration problem that comes in at exactly 1,250 RPM. I have had a smoke test performed twice; once by the dealer and once by a trusted independent. No vacuum leaks were found. Fuel trims record normal during normal operation, but it shows running rich when the problem is occurring and fuel mileage is of course down. On only one occasion it threw at P0171 code. When the car is running open loop the drivability is excellent. The dealer replaced the PCV value which they thought was faulty and at the same time reprogram the ECU, but the problem recurred shortly thereafter and continues on and off.

I would appreciate any thoughts on what anyone thinks the cause of the problem might be. I have been giving some thought to replacing the MAF sensor on the basis of elimination, thinking that its operation may be the intermittent cause.

 

It sounds more likely a misfire. Likely a bad coil. Often contamination and often the ones nearest the engine rear.

Any misfire causes excess O2 (because it didn't burn) so a lean code is quite likely.

 

Hello JDS,

Did you resolve this issue? My car displays the same symptoms so, if possible, I would like to benefit from your experience!