I'm not sure what he is seeing that causes him to say that...maybe there's a lot of carbon buildup or something that he sees. Remember that you were running it with the MAF unplugged for a while and that one of the coils in it was broken for some time before that. The car may NOT be running rich now that you have replaced the MAF. Let me modify that statement a little bit...It may not be running as rich as it was. The stock settings themselves are pretty rich except for the idle settings. At any rate, he may just be seeing some residual carbon or whatever from that original episode. I'm not sure that the unplugged MAF would make it run rich or lean but would suspect that the EEC would know that the MAF signal was way out of whack and would discount it and go into limp mode which should be pretty rich to try to avoid further damage.

If you have an adjustable fuel regulator, there is a chance that it could be turned too high. If it is the stocker, then the MAF is the only thing I can think of...ummm, maybe a kinked fuel return line could cause a rich condition too.