Hey folks,
As the thread title notes, I am trying chase down the cause and hopefully fix a misfire issue that only happens until the car is at operating temperature. Once warm, this issue goes away (as checked by watching VCDS cylinder misfire counters). Until then, the misfire is very perceptible (butt sensor can feel the hesitation when driving and the misfire counters will roll over and reset to zero several times).
When watching the misfire counters, cylinders 2, 3 and 4 had no or very few misfires. Cylinder 1 had virtually all misfires and that counter rolls over and resets until the car is warm.
The car has new plugs and coils. This work was done recently because cylinder 1 was showing misfires before this. These new plugs and coils have not solved the issue, nor have they changed the cylinder that is misfiring - still cylinder 1.
Since capturing a recent VCDS auto scan, I've removed and cleaned the throttle body and where possible removed and cleaned intake piping (some oil was noted in the throttle body intake pipe when I had it off, so it got cleaned, as did the pipe between turbo and intercooler). I debated on removing intake manifold to check for carbon buildup, but elected not to and instead sprayed carb cleaner into intake manifold and let it soak. Kind of a 'hail mary' but it was done anyway.
Other faults were found in recent scans - one in particular was noted and fixed. The ignition switch showed a couple of faults, so it was changed out. This change has had no detectable impact on the misfire issue.
After the cleaning and reassembly was completed, the next time the car was started, and every time since, the misfires are now happening in Cyl 3. Cylinders 1, 2 and 4 have very few or no misfires at all.
So... some carb cleaner and a throttle body clean seem to have moved the misfires from cylinder 1 to 3?! Not at all what I had expected - I figured if anything, the misfires in cylinder 1 might abate, but not 'relocate' to another cylinder.
Also, I cleared all fault codes when cleaning the throttle body. Throttle body adaptation was successfully completed. All subsequent auto scans have shown no Group 1 faults, but the misfires are still present and at levels that are similar to what they were before (although in cylinder 3 now, according to what I've seen in VCDS misfire counters).
In summary, the misfires clear once the engine is at operating temperature, and these misfires are presently on cylinder 3. Once warmed up, the car runs great, pulls strong. MAF shows just under 150 g/s when WOT in 2nd or 3rd gear.
I'm looking for suggestions... What else of relevance can be monitored in VCDS to help identify the misfire cause? What else can be done/checked/adjusted on the vehicle to help with this? All ideas will be welcomed.
Many many thanks in advance for sharing your thoughts.
Cheers,
/paul
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