I have a 1993 940 with a B230F engine which is displaying a persistent fuel code 223. The book says it's "Idle Air Control Valve Signal Absent or Faulty".

It starts, drives & idles normally and the fuel consumption is right close to the EPA estimate. The idle is smooth with only a little bit of speed hunting and it also idles normally with the air conditioner engaged. The IACV is the two-terminal variety, (p/n 13895570) and it works. If I put voltage on the terminals, the valve opens. (verified on the bench) Back in the car, the engine quits immediately when I unplug the IACV's electrical connector. The engine will restart only if I have my foot on the throttle pedal and it quits again when I let off.

The only sign that there's actually something wrong with this engine's idling is the mixture. During fast idle, (1200-1500 rev/min, manually forced with the pedal) the exhaust is stoichiometric and steady. Left to idle on its own, it enriches to about 12:1 and the analyzer indication is twitchy. Not cyclical, as if one cylinder were running rich, but random. I don't have an exhaust-gas analyzer which I can use on the road.

Short of the black-tape solution, any ideas?