running and the car is idling.? The car has had a cylinder compressing at 60% for over a year but has always run very well despite this. Suddenly, last week, when starting & backing up, I noticed a bit of 'chugging' and again when accelerating from a dead stop as well as some shaking on the first bit of accelerating. I also noticed a gas odor when the vents, heat, AC etc were on and the car was idling. All of the above were gone once the car was moving. I had a 2-step fuel line cleaning which blew out a huge load of dirt, slidge etc but the smell persisted. There is no change in idling RPM, gas mileage or other performance and, after a fresh tank of gas, the 'shaking' at acceleration from a stop has gotten less. I had a 'quick' diagnostic at an auto parts store last fall 7 was told my catalytic may be going, I had another today thinking this may be it but was told that cylinder 2 as well as 5 was mis-firing. Sort of at my wit's end w/this. Any suggestions?