5.0 missing at idle, but runs fine otherwise

I have a 302 in my 86 Ford F150 that runs great under load and at speed, but has a miss while idling. The motor is in excellent condition with about 10,000 miles on a complete overhaul. Here is what I have done so far:
  • New plug wires
  • New plugs
  • new cap and rotor
  • stock rebuild other than mild porting to remove emission humps
  • shorty headers
  • Added heat shields to plug boots due to headers (misses with and without the shields)
  • Scanned for codes, but found none
This is a speed density, dual plenum truck manifold fuel injected system. It barely passed smog last time.

Anyone have any ideas? :shrug:
 
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If it's SD, you can run a cylinder balance test to help narrow down the source of the miss. With the puter being able to note even the faintest of inconsistancies (what we cant do), it helps a lot.

The CBT is part of the self-diagnostics (you do it after KOER code retrieval). The test wont tell you what component is at fault, but it can tell which cylinder(s) are not pulling their weight, and to what degree.

Good luck.