What I think you are running into Neil is a car that simply runs lean. I suspect that this is typical on the early LH cars, in particular the 2-valve engines.

What is your fuel pressure like? It sounds like it might be a bit low. I mounted a rising-rate fuel pressure regulator on my '85 S2 5 speed [basically the same car as yours] and then set the MAF to a very lean setting. After trial and error, I managed to get the car to run 14.7 at idle, but around 12:1 at full throttle, all the way through the rev range. My rear tires only last a few thousand miles as a result~

I'd check that fuel pressure first.

Good luck-

N

I'm leaning ( no pun intended!) to fuel pressure as well - others have suggested pulling the vacuum from the FPR which should raise pressure and see what that does - simple test -
I'll report back

next suggestion, please!
 

I tried clamping off the fuel pressure regulator vacuum line as suggested - made no perceivable difference. So, I recalled the 'brain' has a link that is not normally connected that is used in areas of bad ( low octane) fuel to alter the map in some way - I'm assuming the link retards the timing for low octane fuel on the high CR engine to prevent pinging, I plugged them together on 89 gas. after a run the A/f at idle went down to 14 .1, from the previous rock solid 14.7 - at 1500 - 2500 there is not as good an improvement, and its still lean - 15 .5, down from the fail ratio of 16.5 - -

Am I making the right assumptions, any more suggestions -
Thanks
Neil

Neil, you don't think it will pass on those changes? That's real close to 14.7

I'll probably go give it a try - i don't have a lot of options left to get the mixture lean - I swapped out the MAF, exactly the same, so i think i can rule that out -
Any other thoughts - anyone????