How does the Idle Control Valve Work? - PeachParts Mercedes-Benz Forum

ps2cho · #1 02-23-2009, 10:50 PM

Can someone explain to me how this works exactly for the M103 motor?

Fighting an idle misfire.

Is there a way to test it? I have unplugged it via the electrical cable and the misfire continued. Any other way to make sure it is functioning correctly?

slk230red · #2 02-23-2009, 10:59 PM

Quote:

Originally Posted by ps2cho

Can someone explain to me how this works exactly for the M103 motor?

Fighting an idle misfire.

Is there a way to test it? I have unplugged it via the electrical cable and the misfire continued. Any other way to make sure it is functioning correctly?

Didn't you have the misfire before you replaced your head gasket? Is the misfire only at idle?
How much current is your EHA and ICV drawing at idle?

pawoSD · #3 02-23-2009, 11:31 PM

I would think that a misfire is either electrical (spark?) or a fuel issue. The idle control valve just varies the amount of air getting to the engine at idle to keep it at an optimal speed....

When my 300E was misfiring it was from fouled (non resistor) spark plugs. I put in a nice set of NGK resistor plugs and it has run awesome ever since.

ps2cho · #4 02-24-2009, 03:12 AM

Quote:

Originally Posted by slk230red

Didn't you have the misfire before you replaced your head gasket? Is the misfire only at idle?
How much current is your EHA and ICV drawing at idle?

Where would I attach a DMM to find the currents?

wbain5280 · #5 02-24-2009, 05:19 AM

The idle control valve works by letting air leak into the intake manifold in a controled manner or modulating it. The Idle Control processor controls this along with the ECU. You can easily tell if the ICV is working properly by unplugging it. If the idle speed increases, it's working. It might be a good idea to clean it.

The EHA on the fuel distributor modulates the fuel pressure between the upper and lower chamber if the FD, under control of the ECU.

The O2 sensor tells the ECU just how much to modulate the EHA.

The fuel pump relay has a processor inside to turn on the pump and activate the cold start valve.

slk230red · #6 02-24-2009, 09:24 AM

Quote:

Originally Posted by ps2cho

Where would I attach a DMM to find the currents?

Plug your meter (in mA mode) into one side of the connector, it has to be in series. I designed a male/female plug for this purpose. Usually a problem in the ICV circuit is high idle.

But, on to your misfire problem. As pawoSD stated, your problem is more likely to be ignition related. Can you describe your misfire condition....is it a miss at idle that clears up when you accelerate?

Of course the obvious things are: rotor, distributor cap, spark plugs/wires, ignition control module, etc.

ps2cho · #7 02-24-2009, 11:44 AM

Quote:

Originally Posted by slk230red

Plug your meter (in mA mode) into one side of the connector, it has to be in series. I designed a male/female plug for this purpose. Usually a problem in the ICV circuit is high idle.

But, on to your misfire problem. As pawoSD stated, your problem is more likely to be ignition related. Can you describe your misfire condition....is it a miss at idle that clears up when you accelerate? yes exactly

Of course the obvious things are: rotor, distributor cap, spark plugs/wires, ignition control module, etc.

New OVP
New Coolant Temperature Sensor
New Voltage Regulator
New Alternator
Injector's+Seals (previous owner + smoke tested)
New Fuses
Non-Resistor OEM Bosch H9DCO's
New Bosch Ignition Wires (checked for arching as well)
New Distributor Rotor + Cap + Housing
New Fuel Filter
New Breather Hoses
Used Fuel Distributor
New Ignition Coil
Used Fuel Pressure Regulator
New O2 sensor
Used EHA Valve
New Motor Mounts
-- Head work done yesterday:
New Head gasket, intake and exhaust gasket, front timing cover gasket.
Head skimmed and pressure tested
New Water pump.
New Valve Guides + Seals
-- Smoke tested for leaks
-- Compression is 185psi across the cylinders
Swapped Jetronic Brain /w used one
Swapped Fuel Pump Relay /w used one
Swapped Cold Start Valve /w used one
Swapped EZL /w used one

^As you can see I'm not sure what is really left. I'm going to test fuel pressure next I guess.

In bold above...but yes exactly what you said. It clears up on acceleration. I was in my dads old Buick Wagon the other day and I felt a misfire on acceleration for the first time -- Mine does not have this! Idle only.

pentoman · #8 02-24-2009, 11:54 AM

The ICV of an M102 (almost certinaly identical) has a 'zero' position (i.e. if you disconnect it) of slightly open. This means that if the wiring system fails then the idle control valve will be left slightly open ensuring your car idles ok if a little high. This information may help you diagnose.
I think that a little current to the ICV closes it up, but then applying more and more pushes it past that point and on to opening it right up.

You can squeeze the pipes going into it - the idle will be caused to dip but the engine should respond by opening the ICV and the idle will raise up again.

I had an idle-only misfire once on a 1986, it was due to the pipe going from cam cover to air cleaner coming loose.

ps2cho · #9 02-24-2009, 01:02 PM

Okay so it realistically shouldn't cause a misfire, only an increase in RPM's if it was faulty, correct?
I have no vacuum leaks as I had the car smoke tested about 8 month ago, and last night sprayed a ton of carb cleaner everywhere and it had no effect on idle speed. I got a little gremlin somewhere...

pawoSD · #10 02-24-2009, 01:48 PM

Have you ever tried swapping out the ignition control unit on the fender? Or the computers back by the battery? Perhaps one of those devices has a glitch thats causing an electrical irregularity....and thus a misfire.?

pentoman · #11 02-25-2009, 08:13 AM

Quote:

Originally Posted by ps2cho

Okay so it realistically shouldn't cause a misfire, only an increase in RPM's if it was faulty, correct?
I have no vacuum leaks as I had the car smoke tested about 8 month ago, and last night sprayed a ton of carb cleaner everywhere and it had no effect on idle speed. I got a little gremlin somewhere...

I believe you should not get a misfire, correct. You could check by pullnig the hoses off and seeing what happens.

FWIW, I have found these CIS cars will run with the ECU removed without misfiring. Throttle response will be a bit weak and cold running will suck, but it shouldn't have a single cylinder misfire or anything. May help you rule out certain problems that info?
Good luck; bear in mind it could be something you thought you've checked!

ps2cho · #12 02-25-2009, 01:51 PM

Quote:

Originally Posted by pawoSD

Have you ever tried swapping out the ignition control unit on the fender? Or the computers back by the battery? Perhaps one of those devices has a glitch thats causing an electrical irregularity....and thus a misfire.?

Yes the EZL is the ignition control unit on the fender.

Quote:

Originally Posted by babymog

Have you pulled your spark-plugs and compared them to look for one that is different than the others?

I haven't since the head removal...but the misfire has been with me since I got the car...I will pull the plugs tomorrow to see if there is any indication if I am running rich or lean.

Quote:

Originally Posted by slk230red

You have certainly done a lot to your car. Your head gasket job was done very well with attention to detail.

Have you checked for any DTC codes?

The next thing I would do is:

1. Test the fuel pressure
2. Measure the EHA Current
3. Test the Throttle Position Sensor
4. Test the Air Flow Potentiometer

That is for sure

How would I test the air flow potentiometer? In the M103, I know there is an electrical connector that goes to the pot, but what does that control? I thought there was no traditional potentiometer on this engine...
Also does the M103 have a TPS?

Quote:

Originally Posted by pentoman

I believe you should not get a misfire, correct. You could check by pullnig the hoses off and seeing what happens.

FWIW, I have found these CIS cars will run with the ECU removed without misfiring. Throttle response will be a bit weak and cold running will suck, but it shouldn't have a single cylinder misfire or anything. May help you rule out certain problems that info?
Good luck; bear in mind it could be something you thought you've checked!

By the ECU, you mean Jetronic brain? With that removed, what components of the ignition system are turned off exactly?

That is always my fear...but if that part was replaced and it made zero difference I couldn't have got a part that was an exact replica of the misfire I experience...any change at all -- I would notice.

Quote:

Originally Posted by pawoSD

He said it was still misfiring after his head gasket replacement, I'm assuming he had brand new plugs in it at that point....

I vote for an electrical irregularity. If I was you I'd have probably had a MB tech diagnose it at the dealer at this point though....

That is the plan if I don't find anything wrong with the aforementioned. Would I get charged astronomical prices for a diagnosis only? I have only been to the dealer a few times for parts and they were crazy prices...That's why I am afraid of asking them to look at the car...

lkchris · #13 02-25-2009, 05:40 PM

A little misconception regarding function of idle control valve.

Whenever a cold engine is started it requires a rich mixture and a little more than normal throttle opening to keep running.

On carb cars, there was the choke blade and the fast idle cam.

On FI cars, there's the extra injector or a computer program to create rich running and there's the idle control valve to bypass a little more air, i.e. creating same effect as a fast idle cam but not actually opening the normal throttle blade. These are both controlled/monitored by an engine temperature sensor input to computer.

Not much action from idle control valve once engine's warmed up, except that it's supposed to be closed. It indeed "controls idle" during engine warmup, but after that it doesn't do anything.

ps2cho · #14 02-25-2009, 06:33 PM

Quote:

Originally Posted by lkchris

A little misconception regarding function of idle control valve.

Whenever a cold engine is started it requires a rich mixture and a little more than normal throttle opening to keep running.

On carb cars, there was the choke blade and the fast idle cam.

On FI cars, there's the extra injector or a computer program to create rich running and there's the idle control valve to bypass a little more air, i.e. creating same effect as a fast idle cam but not actually opening the normal throttle blade. These are both controlled/monitored by an engine temperature sensor input to computer.

Not much action from idle control valve once engine's warmed up, except that it's supposed to be closed. It indeed "controls idle" during engine warmup, but after that it doesn't do anything.

In the mornings when my engine is cold...for about 5-10 seconds I do not have a misfire then it slowly gets worse for the next 10 seconds before it feels the same as when it is warm. Could there be a possibility that the valve is not closing when it should be? Would that be considered a vacuum leak? (I have had the car smoke tested and I have no visible vacuum leaks at all.

Chowbow · #15 02-27-2009, 02:42 PM

Quote:

Originally Posted by ps2cho

How would I test the air flow potentiometer? In the M103, I know there is an electrical connector that goes to the pot, but what does that control? I thought there was no traditional potentiometer on this engine...
Also does the M103 have a TPS?

You can check the potentiometer through the instructions detailed on this site: http://sg-motorsports.com/AFS%20Pot%20write-up.htm

Mine was bad, and I had to replace the whole air flow sensor though because I couldn't find the potentiometer separately. It solved my idling issues but my misfiring issues were resolved through other means. I had to do new plugs / wires / rotor / cap, EZL ignition module (pulling the vacuum line on it, you should be able to hear the air flow), and the last piece was my #5 injector was a little loose and that cylinder was choking up. Found that by pulling all plugs and then realized that the injector was loose.

Don't think the M103 has a TPS, but there is a microswitch for idle. You can see it with the air cleaner off, towards the firewall. $25 cheap replacement. This is more for controlling idle speed rather than any misfiring issues though I think...

Good luck.

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