Anyone ever run into one of these 3.8L engines that just seems to ping (spark knock) any time you are on the gas a little. Seems to do it no matter what the ambient temp is outside and always around 1800 to 2200 rpm in 4th or overdrive. Vehicle runs fine. Mileage has never been more than 20 per gallon since I've owned it. It also has developed an issue with inconsistent return to what should be an idle speed of about 650 rpm in gear. Sometimes when stopping at a light it will be around 525. Touch the gas a bit it will bounce back up to where it should be. Thought this might be wear in the throttle body shaft. Over the year I have tried an IASC motor, pulled the throttle body off and completely cleaned it and the intake. Never made a change to any of the two issues. The spark knock is annoying with the windows down rolling along at 35MPH. Plugs always look good. Got 190K on it now and need to do a water pump and power steering pump. Wondering if a weak cam sensor could cause this. No codes to find except an occasional evap code from the vacuum pump once in a blue moon. The reason I ask is the last few weeks it has "burped" or suddenly stumbled like it was going to stall when accelerating and it has also suddenly dropped idle speed in gear and then recovered itself in a few seconds.