Okay, here we go again. After sorting out the cold start issue on my girlfriend's 190e, there's been an intermittent problem with the idle. It certainly idles too high, around 1000-12000 rpm. Also, on hot days, there is often an idle surge of about 200 rpm. When the car is first started, it idles at about 1500 rpm and settles down after a second.

I have some experience with CIS, but none with CIS-E. There's seems to be more than a few differences between the two systems.

On this 190e, when I unplug the connector to the IAC, there is no change. On the CIS cars I've owned, the unplugging of that connector would usually cause an idle jump to 2000 rpm. Is this not the case with a CIS-E car?

Also, when I pinch the vacuum lines running to the IAC, the car stalls out. So I'm guessing the IAC isn't closing. Google searches have pointed me to the AFM potentiometer. Is there a test that car be done to the potentiometer?

Any help/advice is welcome and appreciated.

I would check the idle switch.

There is a throttle micro switch that get "hit" by the throttle linkage. If this is not "hit" the car will idle high.

Your switch could be faulty or not being contacted by the throttle linkage.

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Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

replace the over voltage relay. it powers the idle valve and when disabled, the idle motor goes wide open.

to ACCURATELY diagnose the tps on the afm, you need a scope. pins 2 and 3, I think, it's been awhile. there's a 5v reference voltage and a ground. the 3rd wire is the return to the ecu. look a constant upward slope as the afm opens. good luck, chuck.

OP should test the voltage and see whats going to the IACV first before just replacing parts. I dont recommend a "throw parts at it" approach. Test first. Understand whats going on and then buy stuff.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Tests are what I'm asking about, but my usual approach is to throw parts in the air. I'm not sure sure on the proper testing process. I sell parts for a living, so I usually have a bunch of stuff hanging around. Not so with this car.

I'm considering buying a 190e parts car and just doing a fuel system overhaul on this car. Oil has been blowing out of a disconnected hose on the valve cover vent for some years now. So I really want to disassemble the system, clean it and reassemble the whole thing. I am unsure at this time whether or not actual parts are at fault, or if the oil soaked and heat baked wiring may be the cause.