No power to ICV?? (tested Properly!) - PeachParts Mercedes-Benz Forum

350SL4spd · #1 07-18-2009, 11:38 PM

Hey Guys,

I have been trying to chase down a classic case of SSS on my W124 recently and while testing every component I can get my hands on, I have discovered that the ICV is not getting any juice.

I tested it with the plug attached, just pried back a touch, and found exactly 0mA. I know that I should be looking for 600-700mA. I checked the fuses in the OVP (good) then swapped it out for a known good OVP (same result).

The real nail in the coffin is: The idle doesn't change at all when I disconnect the ICV. (Should increase, right?)

Where is the fault here? Am I looking at bad wiring? (Do not tell me my computer is toast!)

Just for background info: My version of SSS is that the car sometimes stalls as you're approaching a stop or turn, but it happens right when the tranny shifts down from second to first. I know this is exact point because sometimes the computer catches it and revs the engine slightly when you feel the 2-to-1 shift and it doesn't stall.

I've also recently had problems with running the A/C at a stop; the idle drops dangerously low.

Any advice?

Thanks!

Oracle12345 · #2 07-18-2009, 11:47 PM

check your wiring, grounds, continuity and yes the pcm is not to be counted out of the picture

mak · #3 07-18-2009, 11:49 PM

the ICV can be tested by removing the connector momentarily applying 12 v to it directly . a click and movement of the valve conforms operation.
throughly cleaning with a can of carb spray normally frees up siezed innards.best to remove the unit from the car
mak

350SL4spd · #4 07-18-2009, 11:55 PM

I will check the ICV itself to see if it has freedom of movement, but I think that w/o power...

I am currently digging for my wiring diagrams to see where it grounds & where to look for shorts (any know problem spots?).

I must admit the cars runs admirably w/o it, other than the occasional stall...

kiwi_bloke · #5 07-19-2009, 04:39 AM

I'm guessing here - but if the OVP was faulty wouldn't this stop voltage getting to the ICV?

350SL4spd · #6 07-19-2009, 11:00 AM

Yes, it would. If it failed outright, it should also light up the ABS light in the dash.

To eliminate this as a possibility, I swapped the OVP w/ a know good one and still had no voltage.

Oracle12345 · #7 07-19-2009, 11:05 AM

take an extra battery or use the battery in the car, take 2 test leads and touch them to the 2 pins on the icv and see if anything happens

350SL4spd · #8 07-19-2009, 11:15 AM

Is it possible that if the ICV is dead, that that there would be no current at the switch? Like how if you unplug the connector you will not see any current?

350SL4spd · #9 07-19-2009, 12:23 PM

Upon further inspection of my wiring diagrams, I see that I was looking at a 1988 wiring diagram. After finding & inspecting a 1991 diagram, it seems that the OVP is not in the proverbial loop with the ICV; the ICV connects directly into the CIS-E controller on my car.

Now if only I could find the damn CIS controller...

350SL4spd · #10 07-19-2009, 01:29 PM

OK.

The ICV functions as it should with 12V applied to it (by me). I have continuity to the proper terminals on the CIS controller (no broken wires).

After these tests, I started it back up and check for power at the ICV. I had 6-7V.

I switched my meter to mA and went to test and as soon as my meter hit the terminals, the engine coughed and immediately dropped from cold start (high idle) to very low idle. After this point I could get no V reading at the ICV.

Now, I don't know if my meter brushed the housing in the ICV as I touched the pole. This would make a certain amount of sense, as the ICV seemed to settle into some kind of limp mode immediately. If I had done this last night, it would explain why I could get no reading at the ICV and why unplugging the ICV had no effect on idle speed.

So now I am waiting for the car to cool down & the computer to (hopefully) reset itself so I can try again. This time I will use a different set-up to make sure that I don't ground out (not that I'm all that sure I did the first time...).

I have a two other tests suggesting that the Throttle Valve Switch may be faulty in one position, but I can see no way that would effect idle with the A/C on...

[rant]Don't you just hate finding out that you spent the last 12hrs chasing your damn tail?!

Especially when you only have 36hrs of garage time...[/rant]

350SL4spd · #11 07-19-2009, 02:02 PM

Just tested the ICV again. I had a steady 5.88V @ idle (might not have been warmed up totally...).

But as soon as I touched the same meter to the terminals set on '200mA' the engine changes speed and I have no miliamps or volts at the ICV. I am absolutely sure that I didn't ground out this time.

I tried with two different multi-meters to make sure mine didn't have a short in it.

I have absolutely no idea what would cause this.

Does anyone have any idea what the Voltage is supposed to be at the ICV? I have only found figures in mA, but that isn't really working out for me...

Arthur Dalton · #12 07-19-2009, 02:32 PM

You do not measure current like you measure Voltage... current has to be a series measure , so you have to open the circuit for meter reading [ polarity sensitive on DC circuits, too]

If you are simply using the meter leads the same for V and ma., you are shunting the circuit with the meter.

350SL4spd · #13 07-19-2009, 05:27 PM

First of all: Thanks Arthur for waking me up.

Second off: I knew that. Sometimes I get my head so wrapped up in what Mercedes did, I completely forget what I'm doing. This is why I always test the same component several times over multiple day before replacing it...

Back to testing...

MAYFAIR · #14 12-28-2012, 01:25 PM

hello

alan here from Durham in england ,did you finaly solve your icv voltage problem ?

i have a 1991 r129 500sl with similar issues ,the icv functions on applying 12v on the bench and intermittently activates of its own accord ?

tested as forums suggest at pin 3 on the inner wing diagnostic port for the injection system (k e jetronic mechanical) they advise should be approx 6 volts
but only showing 0.8 volts ,have checked and double checked ovp relay and continuity from engine connector that sits next to ecu down to idle cont valve -all ok.
just getting weird readings at 2 conectors on icv .VERY wierd thing also is if
put my home made blink tester on the car and put 3rd wire into pin 3 on the 16pin diagnostic plug it clicks the icv into action ????

if anyone has similar experiences please help as spent hours and hours on this fault

cheers for any advice given