1989 Porsche 944 Turbo S - 114,000 miles 2.5l

I am just completing maintenance and upgrades to this car. The upgrades include complete fuel system with 55# injectors to replace the stock 34# ones; 4" exhaust with dual port wastegate and electronic boost controller; MAF to replace the stock AFM with chips for the setup. I also have a apiggy back fuel controller and AFR meter.

Maintenance has include front seals and belts; water pump and hoses (15).

fuel pressure is fine.

I'm having issues getting it to run correctly - it is running very lean. 18+ at idle. I've put in a couple of richer maps but they don't make much difference so I hooked up the fuel controller.

The readings from the MAF and throttle position sensor seem to be as you'd expect. The MAF should read 0.7v at idle. I've increased the fuel accross the board (the corrected reading from MAF to EMS is now approx 0.9V).

It now runs at around 14+ at idle and I can hold it at up to approx 2500 rpm without too much problem. I can go over 2500 if I give the thottle a quick jab (up to 3000 or so).

As soon as I try to hold it over 2500 it goes very lean again. If I adjust the cells that correlate to the cells for the MAF voltage corresponding to that engine speed (no load), it goes lean again. 18+ and starts to run rough (like a solid rythmic miss). The only difference resulting from richening up the map is that it will run rich for a short time as the throttle is released.

Given all of the above, I'm expecting the timing may be out a few teeth. If it was a spark issue, I would expect it to be rich rather than lean.

Am I on the right track?

What is the best way to test this?

What else could cause this problem?

Many thanks, any suggestions would be much appreciated.