Inconsistent Idle

My '03 Jetta wagon has developed an inconsistent idle. usually it settles in at about 950 RPM but it will sometimes idle at 1100 RPM.

What magical box controls idle speed?

I have had a P0128 code for a long time but no change in running temperature and no change in mpg fuel consumption. Bought a coolant temp sensor to swap but have yet to get to it. The idle issue is a more recent development.

Ideas or suggestions?

Thanks.

JohnD

The magical box is the Injection Pump, but usually the Quantity Adjuster to be specific. If the QA is sticky it could cause erratic idle; I have never heard of the temperature sensor causing erratic idle before, but that really doesn't mean anything...
It certainly would not hurt to change the faulty sensor before delving into anything else.

It is possible the Injection Quantity setting is incorrect.

Research hammer mod.

scan it . the temp sensor on the ecm side is reading too low . these will idle up when the sensor reads below a certain temp. seen it first hand on my own alh. also would glow the plugs for 8 to 10 seconds on an 80 degree day lol

Swapped out the CTS. Idle back to normal and after a few cycles the CEL even stopped "coding" me. Glad it was not something more complicated!
Thanks.
John

Thank you for posting back solution!
Is your '03 Jetta variant a VE or PD?