About a week ago my car was running crappy. It stalled out a few times( Some while I was driving). I would floor it and it would get up to like 3000 RPM then like turn off but turn back on at 2000 RPM. Basically the car woulld go up to 3000 RPM, then I felt the car hold back and watch the RPMS drop.
A few days later, the car ran normal( with maybe a little more vibration). Today it started to act up again. I would hold it steady at 2000 RPM and I could hear the engine dropping RPMS( While looking at one of my aftermarket gauges)down to 1900.
Also, when I'm in 4th gear and I floor it( above 50), I can feel the engine shake badly. It only happens in 4th gear but the tranny should be good because I just got it rebuilt.
I'm thinking the car is dropping a cylinder. Would the opti do that? or could it just be a plug? I would get the engien checked but My light don't work and I tried to get my engien read before but they couldn't read it.

 

How about a little more info on your car.... like the year, tranny type, and any major mods to the engine.

 

I thought I wrote it in my sig but Guess not.
93 Z28 (A4)
Borla Exhaust
JBA Headers
MSD 6 Box
MSD Super Conductor Wires
Cam( came with car, dont know specs but Probably a LT4 hot cam kit)
1.6 Roller Rocker Arms
F.A.S.T. Chip
K&N CAI
!CAT, !EGR
Shift Kit

 

Can you take some fuel pressure readings with Key to "on", at idle, and driving around? Mite help us alittle, could be spark or fuel related i would think. Stock fuel system still?