Hi all, I have an almost bone-stock 1993 Trans Am with 92k miles. My engine intermittently misses/stumbles hard when I rev it a little above 3k RPMs, usually when it's warm and in a closed loop. As far as I have tested, it won't miss when it's in an open loop at 3k RPMs, at least so far that I've tested. There are no codes, and my scan tool shows that the long-term and short-term fuel trim are all close to 128. Oxygen sensors both read the same. On average it's in-between 400-800mV. The car idles really well and drives very well up until it hits 3100k RPMs. I can just throw it in park and hold it at 3100k and it will just miss like crazy sometimes. When I drive on the highway and try to give it a good amount of gas, the car sometimes won't let me accelerate anymore as it feels like it's missing and I lose power until I let off on the gas and try again which it usually lets me accelerate then. Again this problem isn't consistent. I can pretty much drive this car no problem, unless I need to accelerate hard. Sometimes I get acceleration issues when at a stop and trying to accelerate hard when the light changes. I also had white smoke coming out the back of the car at one point during a cold start and it was quite a lot. It always smells like raw fuel at the tailpipes, and its quite strong. Not sure if such a strong fuel smell is normal on these kinds of cars. Also the spark plugs keep getting carbon deposits built up on them, each time i clean them.

Things I have tried doing:

• Replaced O2 sensors as they were both original.
• All spark plugs were fouled with black carbon deposits on the plugs so they were all replaced. The plugs looked like they were wet black and not dry black, they were shiny. They are Iridium MGK. I gapped them all at .50.
• New ICM and coil.
• Reset Fuel Trim
• New MAP sensor
• Fuel pressure test and that is within specs. To test that I hooked up a test pump to the shredder valve and measured the fuel at key on and pump priming. Fuel pressure holds steady and within the 41-47 psi range. When started, fuel pressure drops as it says in the book by 3-10 psi. I have not tested the fuel when throwing it in park revving it to get it to stumble/miss and seeing what it reads.
• The fuel filter and fuel pressure regulator were replaced.

All plug wires were replaced with bigger wires when the new Opti was installed (under 15k miles) and all wires look good. I have not looked under the car at night to see if there is any arching of spark.
EGR looks like it's working correctly. I checked for vacuum and it holds very well. Pressure drops when the car starts which is what the factory manual says it should do.

The fuel injectors are still original as well as the fuel injector seals.
The fuel pump is also original.
The catalytic converter is original.

Any ideas where to look? I really am hoping the Opti isn't bad for the third time as I already replaced 2 OEM ones and then switched to the vented Petris Opti which I spent a little over $500 on...
The Opti has less than 15k miles on it, and it has a petris vented Opti. I have the ICM mod, where it is spaced out from the engine block.

 

I revved it for a bit again while it was sputtering and it also ended up backfiring once. I revved for about 40 seconds and saw oil under the car. Wasn't too much but there was enough. Lots of white smoke out the back in a cloud.

 

I just looked under the engine and i see oil on the EGR and the back of the intake manifold gasket looks all wet with fresh oil. It's dripping down the back of the transmission. Could a badly leaking intake manifold gasket cause all these problems?