My dad pulled up in the yard this afternoon with a sick brick. Have a 90 740 non turbo that has lost power under acceleration. Problem started over several days and got worse. Starts and idles fine. Put it in Drive and feed gas and it stumbles and hesitates and has no power and often cuts off when your foot comes off the gas as at a stoplight. We have switched the following parts from mine that are good w/o any success. Have read through the FAQ but am missing something.

Battery is new ( 1 month old) cables in good condition
FP Regulator replaced in Janurary 03
RSR relay switched with known good one (no improvement)
Regina coil pac switch with known good one (no improvement)
Fuel pump relay ( new one installed) no improvement
fuel pump sounds normal at tank
throttle position switch clicks when the throttle pulley moves
Air bellows from air cleaner to throttle body in good condition (replaced last year)
Contacts to RPM sensor, IAC valve clean
fuel injectors all "click" when idling
Fault code = "signal from IAC valve faulty or absent"

What am I missing? Is this probably an IAC valve problem? Any thoughts appreciated.

bruce