I am having some small varying issues that I feel may be pointing to my ECM possibly being on its way out. 1987 vette, 110k miles, been working on it a while now. Here is what I am experiencing:

1- Idle Issues: Replaced my IAC, o2 sensor, set timing and TPS with minimal idle speed. Cold start has me starting around 1100 rpm and climbing to 1400rpm and staying at about 1300 rpm even when fully warm. The idle refuses to set to a normal idle speed after reaching operating temps and it will throw a code after a few minutes at 1300 rpm (code disappears so I am not sure what it is). I need to shut down and restart to get it to start at 1200rpm and work its way down to 7-800 rpm (all in P) after a few minutes. Idle surges mildly in D from 5-7 at times, mostly holding at 600rpms. Thinking maybe my IAC could be a bad replacement, but I am not sure. Throttle body is pretty clean, not sticking. Seems to be more of a computer or sensor driven issue rather than mechanical.

2- Erratic interior lights: My dash and radio lights do erratically flash at times. They all work properly and my alternator is perfectly operational. Unsure as to why this happens usually, checked most my grounds and they are clean. Fuses are fine too.

3- Running Rich smell: Just smells like it is running rich, no related codes or other issues. I am just aware that a going ECM could be causing it to run more rich than usual. This has not become a larger issue, yet.

No vacuum leaks, new gaskets on the intake, fresh battery, I replaced the fuel pump/filter. Only other known issue is my oil pressure sensor is bad. It looks like my issues are probably more computer issues rather than mechanical ones, but I've been known to be wrong before. Any help is appreciated. Thanks

 

I checked my code out now, it has stored a code 22. Will check what the TPS is reading at. I had it set to 0.54v

 

Regarding the first item:

Code 22 means that the tps a/d value is < 12 or 0.23 volts. Something is wrong with the wiring, sensor or connector.

With a tps error code present, the tps will default to an a/d value of 48 or 0.94 volts. This may be enough to get the IAC to follow the throttle and pull up the idle speed. Otherwise, I would say that your IAC is intermittently getting out of phase with the ecm. Maybe sticking a bit when cold or when moving slowly in either direction. Shutting down and restarting is cycling the IAC fully open, fully closed and then opening again to 144 counts, so it should be synchronized after a restart and have a chance to control the idle rpm if it can move freely and stay in synch.

Fix the tps first and reevaluate the idle behavior.

 

Before messing with tps, minimum air rate or idle speed with IAC fully extended. Idle should be around 500 rpm. Min Air Rate needs to be verified prior to replacing or adjusting tps, so it is not a waste of time.
I believe there's a sticky describing procedure.

 

Before touching anything, get a scan tool to make sure it's going into closed loop. There are other sensors that can affect that. Just the fact that it's running rich is an indication that something is amiss. Also check fuel pressure and the regulator to make sure it's not leaking into the vacuum hose. That will also cause a rich running/idle issue.