You've checked about everything else, so:

1) Check all vacuum lines for leaks.

2) If you can find a MAF sensor that you know is working correctly, try swapping it. There is a resistance test for the MAF, but I don't think it checks all of the MAF functions.

3) Check the wiring harness and connections to the MAF - "lordtrunks" was having a similar issue and just PM'd me that he found the problem - someone had hacked the harness and left bad connections.

4) Cycle the MAF connector a few times and/or use some electrical contact cleaner spray on it.

Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum