1997 Taurus 4 door 165,000 miles runs great but not at idle

when at idle it will run good then suddenly spudder lights run dim then it goes back to running good. it does this every like 5 seconds almost in a cycle.

car has new spark plugs, spark plug wires, fuel filter, alternator and belt, battery, and has had water out heet and fuel injector cleaner added. oil changed every 3000 miles with full synthetic Mobil 1

its way worse when really cold here (0 degrees F or less) and once the overflow for the rad was leaking onto the belt causing the alternator to act up. replaced both alt and overflow and then this problem started a few weeks after.

I'll bet it's the alternator. I went through 2 or 3 alternators on my first vehicle('77 dodge Diplomat)
I was told when your alternator goes bad it's common for your next one to have problems too.

But i just changed the alternator out for a brand new about a month and a half ago.

Then again i could have it tested or i could just replace it since it has a lifetime warrenty on it. its free to do :lol:

Sounds like you might have a vacuum leak that's causing the idle speed to drop, therefore the alternator output drops, the lights dim, the PCM compensates by opening up the IAC a bit, and the cycle repeats.

I'd start by performing a thorough visual inspection on the vacuum lines and intake air tubing. You might also remove and clean the Mass Air Flow (MAF) sensor.

-Rod

I have an '02 that is doing something very similar. This is the "vulcan" with 63k miles, and only does it in park/neutral, and only occasionally, but more and more often now. In my case though, it actually dies after a few cycles. I think shorod is right about the vacuum leak and MAF sensor. I had also thought, possibly, ignition coil?