vern1

Thanks for the comments and agree with what you said. The thing is, its such an irregular occurrence its hard to see that its any of these issues.

If you had a faulty MAF or TB, then wouldnt it have a more consistent effect? And a cycling A/C in normal operation would not have this effect as its very noticable ie not like when you are at idle and can feel when the A/C comes on/off - it is a very pronounced surge of several hundred rpm

I dont have a duramatic to track live values so will see if anything comes up at my indy. Then again its not something you can replicate at will. Maybe it wont happen again for another year!

TheBruce

Hi Swandolin - one of the simplest things to rule out is the gas cap. This happened to me twice and its been from a bad seal on the gas cap. The seal can dry out after 10 years and a replacement cap solves it. I had another time where i caught the plastic lanyard under the corner of the cap when screwing it on. Instead of unscrewing the cap I just yanked it out. This was enough to cause the car to buck a few minutes later.

If it does it again, pull over, unscrew the gas cap and screw it back in with 3 clicks. If symptoms go away you have found your culprit.