I bought a 93 that had an issue with stumbling, had codes for o2 sensor, IAC, TPS and intake charge temp sensor. Changed them out, truck ran fine. Unhooked the battery to clear codes, then it wouldn't start, started with a shot of ether then ran ok, but shift points to were way high. Put the old TPS in, started right up, shifts fine.
Noticed it wouldn't high idle when cold, have a 998 and 13 code that weren't there before, checked the connector at the iac and had 16v, tested at the battery terminals, 16-17v. Bought a new alternator, had 14v. Messed with the IAC again, all of a sudden have 17v. Checked at the battery teminals, have 18v from the new alternator.
Pulled the regulator off another pickup, left the IAC unhooked, still have 17v at the battery.
I'm stumped, about to light it on fire and walk away.

 

Codes do NOT mean to change parts, and you're not reading the codes correctly, anyway. An EEC cannot produce both 2- and 3-digit codes. Put all the original parts back on the truck, and read each of these captions a few times:

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