I've been having this problem for a while now and wondering if you guys have any insights on what I can try next. You can check my sig to see my aftermarket parts I have. What I dont have listed is my BBK 52mm throttle body upgrade. My issue happens when the car is warmed up and driven for about 20 min. When I'm stopped I can smell fuel/exhaust coming from the bottom of the car. The more I drive the worse it gets and I also have the issue of a stumble idle but not enough where it'll die. When I step on the gas while in park and I rev the engine I get a little hesisation at first and then It'll rev up fine.* I've just bought a new MSD ignition coil and box cuz I thought that might be the problem but didnt help.* The performance does not seem to be affected but then again I'm going by seat of the pants feel so It hard to say if I'm losing any power or not. My idle is around 600rpm. Im thinking 3 things:1). Something in the exhaust system might be loosed or cracked and Ive visually checked it and only had to tighten the collecter on the drivers side a little. 2.) Maybe my bigger throttle body is throwing off something but I always thought the 58's were not good and the 52's were pretty much the size of the intake holes. Maybe the air-fuel ratio's are thrown off?** Im thinking of doing a dyno tune to it but that might be my last option cuz its damn expensive.3.)The charcoal canister on the drivers side of the car...I'd hate to do this if a hard job but if you guys think that'll help I will do it.The engine has just about to hit 89000 miles and has a new opti (obviously), timing chain and some other bolt on things but the main block and internals are stock and could it just be the engine getting tired?Any help would be appreciated. Thanks everyone in advance.

 

By saying "not raw", I assume you are trying to indicate its a rich exhaust you are smelling. Even with a rich exhaust, its unusual to have it smell inside the car. Where does your exhaust system end? Do you have a cutout?

Misfires cause the engine to run rich, as will exhaust leaks before the O2 sensors, or even a faulty O2 sensor. If something is telling the PCM that the exhaust is lean (air from misfires or exhaust leaks), the PCM is going to start adding fuel the engine does not need. Might also want to check the vacuum line for the fuel pressure regulator. Pull it off and see if it is wet with fuel, indicating a leaking fuel pressure regulator.

If the problem was the EVAP canister or the hoses for it, you would be smelling raw fuel, but you say that's not what you smell. In any case, the EVAP canister is no big deal to replace - jack the car and remove the driver's side rear wheel, and the plastic panel in the fender liner. Canister will be easy to access and replace. But again, canister would cause a raw fuel smell.

Not likely that it has anything to do with the 52mm throttle body. And trying to fix what appears to be a closed loop A/F ratio problem on a basically stock engine with a dyno tune would only be masking the true problem.