"had a engine light ever since that work was done" - hmmm....
Makes me think the work was not done correctly. I've done the T-belt on both of my P2 cars, it's not easy, and since we're deep into diagnosis on yours, and we've eliminated several possible factors, I would not assume that previous work was done correctly...
It may be the VVT, I could be wrong on that, but being off a tooth on the T-belt could cause this too, and given the history, I would start with the timing belt...
2006 Corolla (kid's car - 108K, Conti Eco Contacts, Castrol Edge 5W30)
2005 MB S600 (63K, M1 0W40)
2002 V70-XC (165K, Nokian WR G2, Pennzoil Ultra 5W30)
2002 V70-T5 (143K, IPD bars, Bilsteins, Extreme Contact DWS, Mobil 1 5W40)
1992 MB 300E (Sportline - 123K, Nokian WR G2, Edge 5W40)
1990 4-Runner (V6, 4WD, mild lift - 239K, 31" BFG AT KO, Edge 10W30)
1932 Packard Sedan (straight 8, dual sidemount spares, original paint and interior, Shell Rotella 15W40)