Hi & welcome to the asylum!
Good stuff by Ron! I had the air duct problem on my 90, among other things. My car sat more than it was used by the orig owner, 8200 miles in 15 yrs! So I had quite a few things that went wrong in my first yr of ownership. To be expected if you start asking all the parts to come back from vacation suddenly! I must have looked like a slave driver to the car after the orig owner! I think it's warming up to me as I bought it presents!
One thing for sure is a Helm manual (GM) is a must & the NetRegistry site for the "common issues" and the "How To " section and the recall & TSB section. All worth reading! Oh and then zfdoc.com for trans info & Marc Haibeck's site for EEC theory. One thing I think Haibeck says about the stock injectors is that they don't react well to cleaning and remember that the 90 thru 92 injectors were designed before alcohol as a fuel additive...that is a cause for coil shorting = no pulse = not correct amount/or no fuel from that injector.
I have a Helm for my 90, so if you would like to know the book proceedure for the fuel pump pressure test PM me and I'll type it up & send it to you. Basically through you are looking for 48 to 55 PSI with KOEO, and 45 to 50 PSI motor running. Start test with cold motor & A/C off. Pull 2* FP fuse, pump should run about 2 sec to prim sys. Gauge should = 48-55psi. Install FP2fuse, both pumps should run 2 sec & psi = 48-55psi. Both steps should hold psi. That's the condensed version.
Do a vacuum check on the secondary port vac sys. Sys should hold 12" Hg. Also if the injectors are the problem a scan tool will tell you alot with the motor in "closed loop" & the tool hooked up. The O2 readings will tip you to bad injectors.
Tom