Afternoon. I'm scratching my head trying to find the source of this misfire. Coil pack has been replaced, HT leads show less than 6k ohms and spark plugs look fine. I replaced the pre-cat lambda sensor today hoping that would sort it as the car runs fine with the temperature sensor unplugged. Am I right in thinking that in models with two lambda sensors, it's only the pre-cat one that deals with fueling?
The misfire started a few weeks ago; after more than an hour of driving at motorway speeds, when going down a hill between 70 and 80 mph, the car would violently judder when I applied gas after the hill. If I lifted off, dropped back to 60 or so, then tried again, the problem went away. It's now spread to Lower speeds and it's particularly bad when accelerating in a high gear after having travelled with no accelerator (down a hill or something). The car will judder and continuously backfire but be ok if the revs get high or I lift off and wait a bit.
Like I said before, when the coolant temperature sensor is unplugged, the car behaves perfectly. I cleaned the mass airflow sensor, but don't want to replace it unless it's definitely the culprit. If I unplug it completely (the mafs) and try to drive, the problem gets worse, but the car is still just about drivable. There are no obvious vacuum leaks. Any ideas?
I'm also assuming that the cat is toast at this point.
The misfire started a few weeks ago; after more than an hour of driving at motorway speeds, when going down a hill between 70 and 80 mph, the car would violently judder when I applied gas after the hill. If I lifted off, dropped back to 60 or so, then tried again, the problem went away. It's now spread to Lower speeds and it's particularly bad when accelerating in a high gear after having travelled with no accelerator (down a hill or something). The car will judder and continuously backfire but be ok if the revs get high or I lift off and wait a bit.
Like I said before, when the coolant temperature sensor is unplugged, the car behaves perfectly. I cleaned the mass airflow sensor, but don't want to replace it unless it's definitely the culprit. If I unplug it completely (the mafs) and try to drive, the problem gets worse, but the car is still just about drivable. There are no obvious vacuum leaks. Any ideas?
I'm also assuming that the cat is toast at this point.