trouble codes

I need a little help or advice. I purchased a 1986 Vette in the fall of 2003. It had 65000 miles, was very clean, and had a few problems. Lots of electrical stuff. I keep getting trouble codes on my electronic spark control, EGR failure, MAS, MAP, and MAT. These codes come and go with no particular pattern, sometimes one, sometimes all, and sometimes in various combinations. I've replaced the EGR, moved the MAT, replaced the electronic spark control module, the MAF power relay, the MAF burnoff relay, oxygen sensor, etc. The service engine light stopped coming on when I replaced the oxygen sensor The car seems to run great, I'm getting 21 mpg and I drive it fairly agressively. I can't help but feel that , something is wrong. I should add that it seems to stay in the open loop mode. My question is, how can I get rid of these codes. It's driving me crazy!!! I don't want to pop for a MAF unless necessary. Could it be my engine control module? By the way, my horn dosen't work and I can't find any information of it anywhere. No fuse location, no wiring diagram, no relay, what's up with that?

I have an 85 (had it since new). I know the 85s and 86s have an inherent defect that the EGR Temp Sensor overheats and contiually sets a code 32 (EGR). I fixed this by replacing the EGR Temperature Sensor and putting a 160 degree thermostat in it.
There is a rubber feul vent tube which is by the feul tank that can rub against the body. Mine rubbed through causing a vacuum leak which set codes and made mine run rough for years before I found it. The 80s vintage Corvettes and Camaros are notorious for this. If there are misc. electrical problems I suspect a bad ground connection somewhere. There is a Haynes manual available for this year and model which I beleive has schematics in it. Are codes still being set? If so what is the latest one set? Reply if you need more details.