This is a regina injection system. Car has 240k miles and has been recently tuned up.

The idle has been surging for about 1 year now. It will go between 500 and 1000 rpm about 2 times per second. It's very rythmic. This morning it was about 35°F in the AM and the car idled fine at about 600 RPM. When I got to work 30 minutes later though, it was surging as usual. What I've done in the last 6 months:

I've Installed air filter, plugs, wires, cap and rotor.
I've removed the throttle body, cleaned, new gasket, checked Throttle pos switch
I've removed and inspected snorkle tube from TB to air box
I've checked for intake leaks in the flame trap circuit
Intake manifold gasket was replaced ~1 year ago when the head gasket was replaced - also probed entire engine for leaks with propane

I did pull the codes when I got to work and am getting code 2-2-3: IAC signal failure. In my experience, these things are quite robust, and usually its something else thats causing the 223 code. But I think I've checked about everything else. It seems that open loop control works, but closed loop control is causing the issues. Any thoughts?

Thanks in advance,

Matt




--
'90 245 252k, '93 945 230k