Why does my RPM fluctuate at stops?

[KH]

99 Ford Taurus manual transmission.  At stop lights RPM jumps from 1000 to 2000 and then back down while lights dim.  Got new alternator 6 months ago and battery has been tested a few times.  No warning lights.  A week ago car went nuts (light flashing almost all warning lights on and car kept stalling).  Got it towed in and nothing was wrong so they cleaned the fuel throttle injector.  Few days ago lights were dimming so I got a full tune up.  Now just doing the RPM thing (now a shorter burst and a bit jerkier)  Car drives but RPM fluctuation constant and it seems to be accelerating a bit slower than usual.  Any ideas?  I've brought it in more than once but no one seems to see the problem (it'll do it and then stop for a few days and then start up again) and happens more at night.

[AnthonyB]

Worst case is that the PCM is fried. However it could be a screwed up ground, but I am leaning towards a bad computer or PCM.

[tonys]

Idle air control is bad. Replace this part with Ford part it will run fine. We have a fleet of Crown vics and Taurus this has been the only repair.

[FordGirl]

I agree with the first poster, it sounds like the PCM is on it's way out. Either that, or you have "green death" somehwere on one of your main wiring harnesses. What doesn't seem to make sense, is why you would have a "full tune up" done because your "lights were dimming". By the way, I'm just curious, you state that it is a '99 Taurus with a MANUAL transmission. In 1999, a Taurus was only equipped with either a 3.0L "Vulcan" OHV V6 or 3.0L "Duratec" DOHC 24-valve V6 mated to either an AX4S or AX4N automatic. No manual transmission option existed. What engine and transmission does your vehicle have? And if it is a manual, could you e-mail me the pictures? Hope this helps.