My 300ce (1990, 104 engine) was blowing black smoke and guzzling gas.

The indy shop replaced the fuel pressure guage. This reduced the smoke but fuel consumption is still poor.

I took it back and they found that although it is now running nice and lean at idle, it's running rich at 3000rpm! The shop can't figure it out yet. Compression is good. Fuel divider looks fine. Engine pulls well through the range.

Any ideas?