1990 Suburban dies intermittently

[SoCalSlaughter]

Hey guys, my truck is a 1990 Suburban V2500 5.7-TH400. Ive been having an intermittent problem of the truck just dying while at lights or stop signs. The truck has a very loud whistle I have found out is the IAC, the whistle will stop if I stick i finger down the air passage. The gas millage also has decreased. The truck will randomly through codes 13 (O2 sensor) and 42 (ECM has lost communication with the distributor). The code 13 with turn on, but once I start driving it will turn off. And the code 42 usally sets when im at a stop for a long period of time, the light will come on and the idle will drop. This has been driving me crazy. Ive tested and replaced everything but the engine. haha Still cant find the problem. The truck also, when at lights will lurch forward sometimes, or the rpm will just kick up and the whistle will get louder, but once I shut the truck off, and start it back up, it will run fine.