97 Bonneville N/A 280,000 kms. Series 2 3800
Car runs great most of the time but over the last 15,000 kms car has been acting up. If cruising at 55/60 kms an hour and give either partial or wide open throttle car will either take off and run great or it may shudder, surge and sometimes even back fire through the intake. This can also happen at WOT from take off. I can not get the SES light to activate, has been scanned 3 times and no codes. At times the car will run like it was new with no issues. Usually works great if gradual throttle is applied, and it will wind up to 180 kms hr. with no issue.
Mechanic drove it for 10 miles really hard with scanner hooked up but although the surge and backfire issue did happen, nothing showed on scanner. Car not running lean.
I have tried with tranny in 2nd, 3rd or drive and always the same symptoms.
Problem can occur every time I floor it or it can only act up every other 3rd or 4th time.
Have replaced wires, plugs, fuel filter, checked out the coils just from the top and all read the same ohms. MAF has been cleaned as well as the plate in throttle body and screen. Problem is still exact same as before.
Not sure if I am chasing a spark, fuel or timing issue.
Very frustrating as I am afraid to pass anyone on highway in case car acts up.