From the symptoms you describe, I think the timing belt was not properly installed. It could be the half-shaft is off a couple of notches. Even though the spark timing is controlled by the computer, the half shaft turns the distributer which feeds the spark to the appropriate wire.

On my '90 240, I had very similar symptoms. I found that the cam timing mark was correct but the halfshaft was off.

Easiest way to check is to position the crank to TDC by lining up the mark on the crank pully with the mark on the timing belt cover. Once positioned, pull the distributer cap off and check the position of the rotor. If it isn't pointed at the #1 spark plug wire then the timing is off.

Good luck