I just did a block up rebuild of my 89 4Eunner 3vze. After I got the distributor in properly I set the timing and went for a short drive of about 4 miles- all was good. The next morning the engine was running a bit fast so I was thinking possibly a small vacuum leak - some hose I left off or that cracked- and drove to work and back (18 miles). That night I checked the timing after looking at all the hoses. The timing was off - way advanced at 1200rpm. So I set it back to 10BTDC. This morning - barely ran. Had to take my sone to school so I did the to work and soon home trip again and wil check the timing again. Any ideas on why it would drift so far? and no - the bolt for the dist is tight.

 

Cap & rotor are fouled. Or you didn't get something right,eg tensioner, that'll effect the valve timing also. Or maybe your TPS isn't to spec and you're not doing the timing at idle, eg ECU not registering idle.

Oh and you're likely in the wrong forum section too. This is Build-up's aka build logs.