Surge / Idle Options

[lsintampa]

75 2.0 FI

I'm in Florida - so the weather outside is somewhat warm (50's maybe right now).

I'll try to be as detailed as I can. I've had this issue since I started driving the car - about 8 months ago. It underwent a motor rebuild - along with some other mechanical repairs.

All hoses are new (air supply, and fuel). ECU and other FI components are original - best I can tell.

When I start the car - it starts right up. At idle RPMs go to about 1500 with a very slight surge (maybe 1450 - 1550).

If I pull the air supply that goes to the AAR from the air filter and plug it, the idle goes down to what I'd expect - about 900 RPM still with a little surge. This is while the motor is "cold" - so to speak. Within like a minute of starting.

As the car warms - just at idle, the RMPs start to come down and the vacuum from the AAR isn't as strong - but still present. However now the surge is crazy - like from almost a stall up to maybe 1200, back down, back up, etc.

Pulling the hose from the AAR - does nothing - I can plug it or leave it and the air filter wide open and there is no change. I put the hose back on - again no change.

I did not let it get to a full warm state - IE the temp gauge just started to move up.

I've heard there are three states (cold, pre-warm, and fully warm) that come into play.

Various tinkering, like turning the air mixture valve to a total closed state, and mucking with the ECU dial has had some success, but at BEST, I get like a 1200 RPM idle still with some surging.

To the best of my knowledge there are no air leaks - at least not from any hoses.

I've some concerns that the air plenum may have some stress cracks around the support studs. But I don't know that would cause the surging? I'd think the idle would just be high - period. YES / NO?

I don't know where to begin to figure out why it behaves this way.

Thanks,

Len