89 420 SEL...

I recently gave my car a full tune-up and checked the specs on everything...

The idle was fine at starting 650/700 rpm when cold, but as the engine warmed up, the idle would slowly creep up to 1000/1100/1200 rpm.

[Note I've only had the car for a year or so and think it has had this problem since I bought it - this is my first time working on the engine as it was in fairly good shape when I bought it.]

After a LOT of electrical troubleshooting to check all the inputs to the Idle Control Unit located under the passenger floor (all working and to spec), and checking for engine air leaks - none... I narrowed the high idle problem down to the ICV as being the ONLY possible cause of the problem.

Although the old valve seemed to be functioning properly??? I also tried cleaning the old valve, but it still had high idle on warm-up.

So I paid the 2 cents and bought a new Idle Control Valve.

Note the old part number (car came with) was...
VDO 408.202/010/002

And the new part number I purchased is...
VDO 408.202.010/001

They both look identical to me. But the new part stays at 650/700 rpm as it should.

So do these valves go bad with time/use?

Or perhaps a previous owner installed the wrong part number valve?

I've found these various ICV numbers on the internet...

ISC 000 141 12 25 MERCEDES-BENZ 408-202-001-001
ISC 000 141 12 25 MERCEDES-BENZ 408-202-001-003Z
ISC 000 141 14 25 MERCEDES-BENZ 408-202-004-002
ISC 000 141 14 25 MERCEDES-BENZ 408-202-004-003Z
ISC 000 141 16 25 MERCEDES-BENZ 408-202-010-001
ISC 000 141 16 25 MERCEDES-BENZ 408-202-010-002Z

And this is the only technical data I can find and only for two different part numbers (not my numbers)...

408-202-010-002C
working point at 1000 mA: 10 ± 1 kg/h
at 550 hPa ± 2 hPa difference pressure

408-202-001-003C
working point at 500 mA: 11.6 ± 0.5 kg/h
at 0.55 bar ± 0.01 bar difference pressure

I have had luck searching google.com using the word...

Leerlaufregler

Like...
Leerlaufregler 408-202-009-001Z