Ok. This will be a fairly long post, but I need to provide as much info as possible. I have a 94 z28. I recently pu headers and cold air intake on it, with magnaflow catback. First problem I encounterd was the Y pipe hitting the frame, so I got prothane motor, and tranny mounts and fixed that problem. Next thing I noticed was that under about 3k rpm, the engine felt as if it had lost torque,and power. I had found(just today) that my EGR flange was leaking badly.I tried to tighten it up, and it was so hard, that I maybe got one full turn of the screw, and it seemed like it wasnt leaking as much, I really couldnt tell cause engine was to hot.After that, I got my computer scaned. No codes came up, and no timing retard. After that I drove home, and was trying to see if I fixed the problem. I gave it some gas, and when I got to around 1500 rpm the car started to stumble really bad. I came to a stop, and the idle went to around 400, 450, and when I let off the brake, without giving it gas in drive, it jumped forward. I got home, put it in neutral, and tried to do a constant rev(around 1500 2000) and it would so drop about 500 ti 700 rpm, then jump up again. It did rain alot last night, and when I opened the hood and felt the air filter, and it was a little damp, so I figured it might just be water. Then about 30 minutes ago, I tried to rev at a constant rpm again, and when the car was still cold, right after startup, it was great. It stayed at the rpm i reved it to. Then after the car got warm, I reved it up, and it would fall about 100 rpm, then jump back up to what it was revving at. Better than earlier, but it only semmed to happen when car was warm.Please can anyone help me. I apolagize for the long post.O yeah. Im not sure if the flange is fixed, it might still be leaking

 

Dry your Filter.
Clean your MAF filaments.
Change your MAP sensor(often overlooked) and check for vacum leaks,cracked or loose hoses on your Intake.

If this doesnt help, then its your Opti..............Naturally.