I feel your pain sir...I have been troubleshooting a high, erratic, intermittent idle problem for months on my 91 wagon as well. As we speak, he is in my garage now being teated for symptoms of high breather pressure. I am changing the front seals due to sudden leakage. While I have him down I decided to remove the intake manifold to inspect further for the cause of this dastardly problem. I did notice evidence of a leaking intake manifold gasket when I removed it...the gasket was crumbly and there was streaking in the cylinder head in some areas indicating some leakage. I am cleaning the excessive gunk out of the breather box hoping to restore some sense to my vacuum system??? I have changed my IAC, ECU, cleaned the throttle body, inspected for leaks in the intake ducts....only thing I haven't done is checked for continuity in the throttle position switch (it is clicking when it is supposed to, just not sure if it is making). Another symptom I have is an increase in idle when I apply the brake to shit out of park. My shift safety switch is giving me problems right now (having to use the override)...maybe this is an indicator to the cause???? I need a miracle as I put this back together...

Mark
3-1991 240's (2 sedans and a wagon)
95 850 GLT