WD40 is about the only thing I have not tried. At this point I'll try anything.

 

has the crankshaft position sensor been changed and an crankshaft variation relearn not been done. this can set false misfire dtc...usually random po300.

 

tech2,
On the misfiring subject,
If you have certain cylinder misfiring in idle and also random misfiring in part (low) throttle then does that say anything about the cause?

 

no the crank position sensor has not been replaced.

 

not sure...
If you have a good scan tool you can monitor the misfire counters live. gm has the best misfire counters i have seen. So although the dtc shows a random misfire at times it not definite that something changed...the scan tool can show you whats going on live....to see if the accumulators count for another cylinder or stay on the same cylinder.

 

So I took my car to a shop. The wonderful roller lifters are the problem. There is also cam damage too. So I'm looking at a rebuild of the top end of the engine.