The story is I installed the ACC in my Mercedes 190D (2.0) and it was a combination of 2.0D and 1.8 petrol acc. ACC works great for two years now, but my main problem that occurs is very low idle speed when climate compressor turns on. I know that on younger cars, there is electronic regulation of idle speed, but I thought there is no option for 2.0D w201. Recently, I read on some article that there is some electro vacuum switch that was built in mercedes 190 for that purpose, but I don't know how it looks like or original factory number.
Does anybody have any picture of it, or the number and correct name so I can find it?
Thank You

I hate to weighin here as this is a complex subject. We have EGR systems here that are vacuum and electronic at once. No other vacuum/acc comes to mind. There are also a pair of microswitches on the throttle control cable that regulate idle, here its for egr. Are those present? I think most of the acc control goes through the klima relay. Thats located behind a panel back of rhe battery. Ive been advised that these old school relays are very sensitive to static, so beware.

Thank You for the answer.
In this tread, on first diagram, there is something called switchover valve for rpm idle increase? Item 127.
http://www.peachparts.com/shopforum/diesel-discussion/285796-190d-2-2-egr-system-vacuum-line-modification-peer-review-needed.html
What is that

This is part of the vacuum/electric control egr system i mentioned. In my 1984 w201, none of this egr functions as it ought, but my ac works and the idle is exactly where it ought to be.

In your vehicle, do you havea vacuum control valve at the injector pump? Perhaps it is defective?

I wont go any further with this since im an idiot about this system and could lead you astray.
It sounds like you have a frankencar, is this accurate?

All 190 D's (I mean 2.0 D) with A/C from factory have ELR (elektronische Leerlaufdrehzahlregelung) system. Description of this system see in the attached .pdf file.
You need to change IP or RSF-regulator (+ add other parts) from the vehicle with factory A/C to instal this system on your w201.

Attached Files

ELR.pdf (256.4 KB, 175 views)

With ELR or EDS, there is an electromagnetic actuator on the back of the IP for idle control. The computer senses engine speed and will not let it fall below spec.

The diagram in Vandeo's post is something else, something I've not seen before. 127 is a vacuum switchover valve (similar to the one in this link), which switches vacuum to a vacuum actuator on the back of the IP. I suppose the switchover is actuated by an electrical signal from the A/C system.

http://www.pelicanparts.com/More_Info/0015408697.htm?pn=001-540-86-97-M244&SVSVSI=3095

Thank You. I have vacuum control valve on IP. There is also RPM sensor and control unit which controls the AC. But, I don't have this kind of valve in Mxfrank post, that will route vacuum to vacuum control valve on IP.