[crazypete]

It's almost always an ignition issue. Check the wires. During install, I've been known to move wires around and then one gets cooked on a header and the spark goes to the frame and not the plug. Insant "jerking". Tonight, turn off the lights, pop the hood and start the car. Look for sparks near the headers.

If not, pop the distributor cap/rotor and see if it's all burnt up. This is usually the cause for me. Finally check the timing.

The ONLY reason that UD pullies would cause engine problems is if the engine was overheating from the reduced water flow. But you would know that from the guage.

Pull the battery cable, let it sit 10 minutes, reattach, take if for a drive, then get the codes when you are done.

All you need is a simple $5 analog voltmeter.

http://www.corral.net/20anngt/images/test.gif
http://www.corral.net/20anngt/eec.htm

You can do a cylinder balance test by revving the engine once to trigger the balance test after all the codes are done and it will see if there is a trouble cylinder. Then you can check the plug/wire for that cylinder.

Have fun!