Title sums it up. When holding a steady 2000 RPM, my car stumbles and lurches. Of course, this would be right around 70-80mph, cruising speed for me. (I'm being forced to cruise at 90 now. *snicker*) It doesn't do it at any other rpm really.. it's a very small band, too. 2250 rpms and the car runs just fine. The plugs are new, as is the cap and rotor. (Coil and wires aren't, though.) EGR's new as well, although I doubt that would cause a problem quite like this. The problems started after I broke my fuel pressure regulator.. I'm running a bit rich now, but not enough to throw any codes. It seems like it couldn't be related to the rich mixture since it ONLY does it during a narrow band around 2000 rpm's.

Any suggestions?

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89 iroc-z 305 tbi
k&n filtercharger, open element air filter. nuffin' else

 

Reading your other post as well... hows the engine ground? It sounds like a misfire to me, its probably running fairly high cylinder pressures at that particular rpm and cant fire the mixture properly.

Just my .02 guess.