idle speed fluctuation

[Troyport]

Hello all, I have a 1987 V20, 350 V8. Methodically tweaking on everything to get it as perfect as possible. Lately been chasing an idle speed that was not stable. Wasn't really rough, just fluctuated very consistently between 650 and 750. Probably took 5 - 7 seconds to complete an entire rise-fall-rise sequence. did the typical tune up, vac leak stuff, cleaning, base idle setting, egr working right, coolant temp sensor within range, grounds, etc. The only thing I had left was the base timing... I checked it when doing the tune up, it was at 4 deg BTDC. I've read where people prefer this, so I left it. A few days ago, as a last resort, I set it to zero as it was easy enough to do. I was surprised to find that it fixed the problem, and I can't reconcile that in my head. coincidence? anyone else experience this? thanks.

 

[JT58]

My idle on my 87 350 TBI idle also fluctuates like this that I have not been able to resolve. I have it in the plan to rebuild the TBI, replace all gaskets, etc. I just have not had the time. It does not do this when I do a cold start. It idles perfectly high and stable. It fluctuates a lot as it warms up, then when fully warm fluctuates only 100 or so RPM. I have not changed the thermostat- I believe it has a 160 deg as the temp runs 160-170 most of the time. I also have not messed with it as the engine runs awesome except only for the idle fluctuation.

 

[Mango]

My Idle is great in Neutral When warm at stop signs or lights it struggles slightly
Warm starts hot it idles low if I turn the steering wheel it may stall I think it's the IAC with almost 200,000 Miles
WHAT DO Y'ALL THINK

 

[Mango]

Repaired! Replaced the IAC and the EGR Problem Better
The IAC was toast I cleaned it with Throttle body cleaner A few months ago I guess that is a NoNo.
The EGR would not hold Vacuum original with 199,289 Miles
Hopefully all good for Now