Volvo: 1991 Volvo 16-valve, vacuum leaks, maf sensor

Question
Problem:  Poor idle and loss of power off the line.

I've changed the MAF sensor (new aftermarket), idle control motor (used), substituted a fuel pump, verified no vacuum leaks, cleaned the throttle body, measured fuel pressure all without improvement.

Once launched, and it gets by the giant hole, it runs fine (over 2,000 rpm).  The exhaust doesn't show rich, plugs look normal, I suspect that it's either running lean or timing is off for some reason during takeoff.

I've not replaced the O2 or knock sensor.  Any ideas?

Answer
Albert,
First read all the fault codes and follow them. If nothing shows up there take the car to a Volvo shop that has the scan tool and the ability to piggy back a hook up to the control to see what signals are missing. If you think the timing maybe off, remember the timing can not be set so that could mean the belt has slipped a tooth. With that in mind the 16 valve engine will hit valves if more than a couple of teeth off. You may want to see about the belt position before going any further. You could also unplug the HO2S and drive to see if it were at fault. Remember that will set a fault code.