I have a 90 3.0 4runner that I just did the timing belt on, can't get it to idle smooth and when I try and do the timing anything below 15 deg doesn't want to run. the cat and muffler are bad and i'm wondering if there is alot of backpressure causing this problem. going to take a hacksaw to the muffler and see how it does

 

With mine the cat was stopped up pretty bad. My exhaust manifold was warped just a little bit and with all that pressure, I was blowing manifold gaskets and melting spark plug wires like you've never seen. Hacked off the cat and never looked back. (No Emissions here)

 

Have you unplugged your TP sensor to see if that may have anything to do with it? Was the truck running ok before the timing belt?