[s-cars] Surging, any ideas...?

[James Murray (QC/EMC)]

Hi, my car is acting strange, I feel a surging while driving at a constant speed. Less noticable on acceleration, but still present, it's like something is holding it back and then it opens up again...it's more noticable if I keep my foot on the pedal at a specific location (try keeping a constant speed), the car will slow down and then accelerate, almost like the gas flow is not constant... I changed my gas filter this past summer so I don't suspect that. It's not an agressive surging, but I feel it, passengers can tell if I point it out.

Any ideas what to check? 

/James.