From "tests ok" I assume you measured the resistance of the MAF. Unfortunately, that test doesn't prove the entire sensor function - at least I don't think it does. If you can get your hands on a "known good" MAF sensor, replace yours for a trial and see if it works better. Absent that, a dealer analyser might be able to read the air temperature for comparison to ambient, but you need to test it with a cold>warm engine to duplicate your conditions.

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