Car runs super rich in P/N, Pulsing on light load

[Fireball]

Hey guys,

I've got an unusual one here...

Some background on the car first:
- 2001 Malibu
- 3100, 200k
- CAI/WAI (depending on season)
- 65 mm tb
- Ported/Polished UIM/LIM
- Ported/Polished/Milled + a valve job on the heads
- Headers (OBX which is a Chinese S&S)
- High Flow CAT
- 2.5" Cat back
- WOT Tech Motor Mount
- Poly filled transmission mount
- Tune

Now, the heads were done not too long ago (2 months or so).
I got the re-tune, the car ran great, hauled arse and was doing great on fuel..

Fast forward a couple of months... under light-moderate throttle the fuel trims are close... Heavy throttle they're only very slightly off..

Idle in drive produced somewhat of a lean condition for the most part (although it can vary wildly).

As soon as I put it into P/N, the fuel trims start to go into the negative and keep getting worse quickly and drastically.. hell behind the car it smells like someones just pouring fuel into there and the car can't pull enough out...

First thing's first, I tracked down a couple of vacuum leaks..

I also get a weird pulse when accelerating... at low rpm/low-throttle acceleration the rpms rise and drop very slightly while the car accelerates (It's not the TC locking/unlocking, much smaller then that).

Note that this problem gets 2-3 times worse when my EGR is active (I currently have it deactivated until I figure out the issue).

While it does that, I notice that the pulse width and MAF flow rate drop as well...

I'm looking into getting a used MAF but am kind of stumped as to why it's running the way it is..

On another note, gas mileage is still great (especially if on the highway), the power still there, but not as much as it was a couple of months ago where it took off and kicked ass in every gear...

Any thoughts?

[TurboGTU]

Unplug the vacume hose off the fuel pressure regulator while the engine is running . Might be leaking fuel through the vacume port.

[ericjon262]

possibly an exhaust leak near the 02 sensor.

[Fireball]

Thanks guys,

I'll check the FPR next time I've run the car for a while and it exhibits the said condition.

I'll also re-torque the rear header and crossover next time I have the chance/room to get things done down there.

Any reason as to why it's worse in P/N than it is in D?

[Fireball]

On another note... I seem to get some smoke off the headers up front...

Is it possible that this is the heads leaking or can coolant leak from somewhere and work it's way down there (lowest point).
It smells like coolant at least... can't be 100% sure.