Contour Enthusiasts Group Archives Forums General Troubleshooting Slight vibration cycle

After the cat has been idling for a minute, it will very slightly cycle with a rough spot that I can feel through the brake pedal. It seems that after coming off the highway and the engine has been worked a little, it takes longer to start the cycling. No tach fluctuations, but I can feel the vibration. Car runs great except for this. No cel. Any ideas? Thanks, John

Slow oxygen sensors do this, should give a code but it may not be quite there yet.

Roger, I replaced both uppers within the last two months. John

I usually would suspect mixture fluxuations.
Slow O2s can cause them, so can vacuum leaks.
A weak ignition system would cause this more readily.
Possibly fuel pressure fluxuations?

A torque converter problem should cause a noticable RPM dip.