backfire in the intake - idle surge - BAD

[trooper8]

94 Exploder V6 AT 2WD surges bad at idle, has been getting worse, now the surge is somewhat evident while driving too. Idle rpm will drop to 400 and very nearly stall. She runs well otherwise and makes power when needed. No codes - 111 pass.

It sounds like it's backfiring into the intake manifold, kinda rumbling, it runs correctly for periods of 5-10 secs and then starts the trouble again.

I've checked thoroughly for vacuum leaks. I've cleaned the MAF and throttle body. EGR working well.

I pulled the elect connection from the IAC and it seemed to be fixed. I replaced the IAC - trouble still exists. I figure the computer is sensing an idle speed reduction and modulating the IAC to try to correct it.

I inspected the plug wires and replaced one that seemed to have a discharge mark in the insulation with a known good one, no change.

My next step will be to pull all the plugs and look for evidence of one that is different, probably just put new ones back in.

What's getting me is there are no codes at all. Help! It'll kill me to take it somewhere and get jabbed for diagnostics and repair I could do myself, but the Mrs isn't going to wait much longer...
Thanks

 

[trooper8]

troubleshooting

Guys,
All the plugs look picture perfect...
HELP!

 

[trooper8]

results

For reference the alternator was throwing voltage spikes and needed replacement. That apparently fried the computer as it diagnosed bad at the shop and was also replaced. Some things are nearly imnpossible to determine by shade-tree methods. Now it's all better.