While its been my most trouble-free vehicle for 180k miles, I recently had to replace the timing belt....no real problem with that.
Soon after, however, it developed a surging sort of idle.  It doesn't have a tach, but by ear it seems to go between 900 and 1400 (approx.) in a smooth sort of sine wave pattern.  I discovered after a while that when I disconnect the vacuum hose from the MAP sensor the idle will smooth out at close to normal but of course the engine will run with a too-rich mixture (though this gives plenty of power and torque...it ruins gas mileage) It revs up nicely and again settles down to something close to normal.  When I re-start with the hose off, it runs even more rich and idles just barely at a very much lower rpm....re attach the hose and it starts the uneven idle and when the hose is again removed it goes back to the smoother but still rich idle.

I changed the MAP sensor with one from a Tracker and it ran as it should for about 2 weeks...then the errant behavior returned.

I've checked the voltage output while connected and it varies between 1.48 and 1.61 (at the extreme, mostly 1.55 +-.02) at idle.

I'd appreciate any (low cost) solutions anyone might suggest.

Stefan

Sounds like the MAP sensor, did you try using the old MAP
on a known good running Tracker or Sidekick to verify a
bad part? It could be you got a bad 2nd MAP as the problem.

You stated the new MAP solved the problem for a short while,
you might want to test this out with another vehicle, I know
if my MAP sensor's vacuum line gets pulled off it runs way to
rich and causes the engine to stall from way to much fuel, so
your MAP sensors might have developed a ruptured diaphragm
inside

Wild

Thanks for the reply;
Somewhere on some forum I read of someone with an idle problem, not exactly like mine...but too high when warm, that claimed to have solved the problem by restricting the flow through the (fast idle?) air jet/chamber (the cylindrical shaped part of the throttle body with the cover held on with the three screws) it was claimed that by inserting a short piece of heater hose to block the air flow the idle went back to normal with the only negative being that one had to provide a bit of extra throttle until the engine reached operating temp.

As I live in Florida this would be a very minor inconvenience, so I tried something similar (using what I found readily available in the glove box) and found that indeed this seemed to have solved it.  I suspect that at 180k miles the little valve at the rear of the chamber quit seating completely. 

The old MAP sensor was destroyed by my curiosity (I dissected the bugger!) but the Tracker one seems to work now. 

Thanks again, I'll post an up-date here if further problems develop and results of effect on fuel mileage.

Stefan

That repair is the Wax Pellet fix, the wax pellet is the high idle device
that lets in extra air, until the engine warms up and it melts, allowing
the valve to move and close, it's quite a common problem to have a
high idle when cold, but it usually drops once the engine is warm.

Yours must be defective to cause a high idle all the time, and the heater
hose fix is a good one to cheaply resolve your issue of high idle, but in
your attempt to solve the high idle, you got sidetracked with the MAP,
and I think you may have destroyed a good MAP sensor out of curiosity,
I hope it wasn't an expensive part

Wild

High? OUTRAGEOUSLY HIGH!.....but I had the good fortune of finding the Tracker one for a measley $6 at a "pick your own" scrap yard.....the last possible candidate in the yard had the part!

Lesson.....test FIRST....then disect!

For a while, I had temporarily replaced the MAP sensor in the circuit with a variable resistor I bought at Radio Shack...sort of dial it it device.

Stefan