89 suburban has multiple codes, help requested.

Just picked up an 89 with 110k, and was told it was overheating.
Did some work on it, found several vacuum lines disconnected and the timing was ungodly advanced , so I traded a couple of POS's I had laying around for it thinking I had found a good deal.
Well, here's what I have so far.

SES light comes on after 5 minutes of driving, but no real loss of engine power or other symptoms.
Did the paperclip test and came up with codes 22(TPS), 32 (EGR) , and 43 ( knock sensor).
22 went away after I de-gunked the TPS, and hasn't come back yet.
I went to swap out egr valve but found the nuts holding it down were only hand tight. Pulled it and did a vacuum test, it worked fine. the original gaket wasn't even crushed so I reused it,but I still get the light.
I bought a new knock sensor so I'll go ahead and replace that and see what happens.

My question is, are these all inter-related or just isolated instances of sensors going bad?
Thanks for the help.

Isolated, The TPS tells the computer how much throttle you are giving therfore how much gas flow. The knock sensor adjusts the timing (slightly) to prevent spark knock (valves rattling like a diesel engine). The EGR problem may lie with the EGR vacuum solenoid, if that is not it, it may be computer. I have an 1988 Suburban with the 454 and get the same EGR code.I replaced the solenoid, but that did not work. On to the EGR valve or computer at the worst.

I have an 88 Suburban 2wd. Got the EGR code as well. I replaced the EGR valve, but still got the code (and engine light after about 8 miles driving). The problem could be elsewhere in the EGR circuit...such as if there is an EGR control module?:rolleyes: