1990 Escort GT Idle Mystery

I have been having this idle problem for a while now. The car drives fine, but the following symptoms occur while sitting at a light, stop sign, etc.
The engine idles between 1500 and 1750 RPMs for 10 seconds, drops down to about 900-1100, wobbles a bit, and settles in that range somewhere when the check engine light comes on.
If I goose the throttle, the check engine light turns off and the symptoms described above re-occur in the same order. I have installed a new TPS, idle air control valve and O2 sensor over the past year. Like I said, it is not preventing me from driving the car, but is darn annoying when stopped.
I have a new tempature switch I was going to install when I got around to changing the oil next, seems like the best way to get at the heater tube situated underneath the lower intake manifold.
Last year I climbed Mt. Washington with the car and it has not been the same since. It overheated at 5000 ft because the fan would not turn on, a paper-clip fixed that temporarily. Wondering if the temperature spike might have damaged the temperature switch used by the computer. It definately fried the voltage regulator, but that is another story.
Can anyone offer any suggestions? I have pulled the codes but mostly they point out an open fuel loop condition, with rich limit reached. I am pretty sure I have pulled these codes in the past before this started happening. I know there is might too much air getting in, but so far cannot find any vacuum leaks. Manifold pressure is about 17-18 psi at 1000 RPMs. The fuel pressure seems OK, around 36 psi.
Obviously it is getting on in years and I should just give up the ghost, but I am not against spending a few bucks on parts here and there to keep it running while it lasts.
Thanks, Matt
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Leak in the air intake...........incorrect PCV flow, common problem.

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Thanks Tom, I'll check it out!
Matt

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Hello Tom,
Replaced the PCV valve and grommet in the valve cover, checked for leaks in the vacuum lines, none found. I capped off the tee in between the PCV valve and intake, no change (not sure what vacuum actuated component the tee goes too, sits underneath the battery). However, I had someone block the exhaust for a few seconds and I think I found a leak in one of the two or three? tubes going in/out of the catalytic converter. I could feel a rush of something coming out somewhere underneath the manual transmission case. I have not pin-pointed it yet but I am thinking this is an exhaust leak but could it also affect the PCV flow? I know of of these tubes goes into the valve cover and one goes into the air cleaner. There might be one more tube, have to look.
Thanks, Matt

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Hello Tom,
Replaced the PCV valve and grommet in the valve cover, checked for leaks in the vacuum lines, none found. I capped off the tee in between the PCV valve and intake, no change (not sure what vacuum actuated component the tee goes too, sits underneath the battery). However, I had someone block the exhaust for a few seconds and I think I found a leak in one of the two or three? tubes going in/out of the catalytic converter. I could feel a rush of something coming out somewhere underneath the manual transmission case. I have not pin-pointed it yet but I am thinking this is an exhaust leak but could it also affect the PCV flow? I know of of these tubes goes into the valve cover and one goes into the air cleaner. There might be one more tube, have to look.
Thanks, Matt

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