Mystery fuel issue S4 Turbo II
 

I'm stumped on what could be wrong with my car. I've had it since last year and the car has been great up until last week.

I'll explain the issues as they happened:

1.) I was on my way home from work and my car began to lean out and hesistate occasionally getting progressively more violent as a drove until becoming undriveable the next morning.

2.) It had some odd issue the next day and the following few days where it wouldn't start as strong as it normally did, kinda grumbled to life and I had to keep it running with the gas pedal until it was warm and stabilized itself. Idle was low though

In an attempt to correct the issues I:

1.) Checked the tps resistance and corrected to spec (wasn't too far off)

2.) Changed the spark plug wires and spark plugs

3.) Checked the AFM voltage and it wasn't quite 4V but close and the spring tension seemed ok

4.) I noticed that the O2 sensor wire touched the turbo at some point and I guess grounded itself so I wired up a new one

5.) Changed the fuel filter out for another factory one and removed the Walbro 255 pump and replaced it with a Deatschwerks 300

So now the car starts and idles as it should, but under light load the hesitation and leaning issue is still there. Its random but happens all of the time and doesn't seem rpm related. I put my foot down a bit to check afrs under boost and it runs rich into the 11's as it should most of the time. When it spikes into the lean area I watch my wideband and it'll go from mid 14's up into the low 15's and hesitate.

I'm lost.

Car info:
87 Turbo II
Factory ECU
S5 turbo
Mild street port
Factory injectors and fuel rails
DW 300 fuel pump
Fuel pump rewire has been done
All emissions stuff has been removed

Any help is greatly apprectiated.
If nothing can be figured out soon I'm going to have the car towed to a local rotary shop called Rotorsports.

Anyone?

The air flow meter is the main device used in determing a/f ratio at any given throttle position/load, so it might be worthwhile to try another one in case one or two contacts inside yours have started to get flaky. I would also consider checking grounds with an ohm meter or just running new grounds...start by cleaning battery posts, clean or replace terminals, run an extra ground from battery to chassis bare metal, then perhaps even daisy chain that ground over to the engine block so you can be sure that it's grounded (this assumes you dont want to actually access the factory ground points and clean those). Then I'd get at the ECU and re-ground the 4 pins/wires listed in section 4B of the FSM on the ECU pinout chart to chassis bare metal.

Sounds like a grounding issue to me.