Idle air control valve m103 question
 

Newbie here, searched for this answer.

91 300te m103 start low idle problem.
When I disconnect the Idle aircontrol valve connector with engine running at 80C the idle rpm drops.
Is this normal?
If not, can I put battery to 2 connectors and observe operation?
Pulled it and it is clean (sprayed carb cleaner and not much residue).
Thanks

Normal?
 

I tried disconecting the icv connector with car running at op temp and my idle went way down! I thought it was going to stall.
I always test mine after cleaning it by hooking it to 12 volts to ck the operation.I like to see it goes full travel I found a bad one doing that test.
Is it normal for the idle to drop?? although mine does I am having alot of problems lately!.......................What symptoms are you having that you are looking at the ICV???

I have a 91 m103 with 325K miles.
Car runs ok after starting, dieing, starting, rpms get to normal but have to wait to put in drive,
So,low rpm and die on first start (starts quickly).
Your symptoms>

I dont think its normal for the idle rpm to drop when the IACV is unplugged.

On my M103 (~100k) the idle rpm (IIRC) goes to 1500 rpms.

On my 420SEL (~220k) the idle rpm goes to 1500 rpm when IACV is unplugged.

I see from your 2007 posts you've been there.
On my 91 m103-
Tested the ovp and everything tests perfectly (several times).
With connector removed, 9 ohms between pins.
Engine on (40c temp) 8.8v between pins, dropping gradually as engine temp warms to 6.5v after a minute or two (just a tic above 40c) when I stopped.
Unplug and idle drops immediately.
Plug back in, no change until I restart the car, then idle ok.
Twice have had someone start the car cold (58f outside).
Starts up but will die unless I slightly hold the air flow sensor plate open, then idles cold fine.
This is driving me bonkers!
Any diagnosis help appreciated!

mine dies also on start
 

My car also starts and dies within a second of starting unless I hold the key in the starter cranking position for about six seconds or more to get me past that dead spot! It makes me think there is no fuel in the fuel distributor,maybe just a little residual in the lines by the injectors to give it that initial start and then it dies until more fuel can be pumped up from the fuel pumps.
In other words I think it is leaking back some how. I think there are check valves by the pumps and also a fuel acumulator back there by the pumps ,one of these may be the problem item.

I thought about that but those pumps are about 1 qt in 45 seconds.
The accumulator as I understand is only to hold pressure for an hour or so.
Try this-
Remove top of airfilter.
In the morning (cold) have someone start the car.
As soon as the round sensor plate drops,and the car fires, slightly hold it there and see if the car doesn;t idle fine.
Tried that two mornings and it worked.
Now, pulled and tested the Idle air control valve with 12v at the battery and it slams open and shut.
If you are worried about the rubber hoses being brittle, just disconnect the plug and run two 16 ga wires from the pos and neg on the battery and touch the terminals.
Apparently the hose to the intact manifold requires much patience and dexterity to rplace if brittle and cracked.
From the front, pos on the left terminal.
You will hear it open and close as you apply and remove voltage.
Will let you know when I figure the rest out..

A little better but not there yet
 

I replaced my injector seals and O rings,and it seems to run better and idle a little better but It still idles a little funny and still has a dead spot while driving cold between 1000 and 2000 rpm the car runs great once it gets hot.
I have recently replaced the hoses for the ICV they were split! after that it ran good for a while and now it is acting up again:confused:
I still feel it is a vacum leak.

For vacuum leak test I use a small hardwarestore propane cylinder with add on valve and tip. To establish baseline, remove an intake manifold vacuum connector and put propane tip at the hole to see what difference it makes in idle speed.
Sometimes, not much, but a change.
Here are the two info testing pieces I used. Accurate.


When you say 1000-2000 rpm what is engine temp?
Might still not be in closed loop.
Different scenarios for acceleration in closed and open loop in my experience.

Still the question- when you unplug the Idle air control valve, your rpm drops hot or cold?

first you have a bad ICV, when you pull the electrical connector the idle should go to to 1900, if not replace it. Second if you hold the air horn plate down just slightly and it runs better! what you did was increase the fuel, so this means that you need a three millimeter alen wrench and turn it c/w to fatten up the fuel. do a search on X11 and setting the air fuel mixture. Replacing the rubber parts is always a great place to start on one of these cars, they get hot under the hood and all the rubber connection parts need changing after 20 years of service, it is cheap but labor intensive, oh yes do not for get that every moving part connected to the heater/AC system is operated by a vacuum module with a rubber diaphragm, they to get worn out. The fuel pumps should turn on with the key and run for about 3 or so seconds this is prime mode, though the fuel accumulator dose not hold max pressure it dose hold some pressure, even over night. Hard start could well be that all the reserve pressure has dropped off and that prime mode just is not long enough to do what we are asking it to do, there fore a long cranking period. When you have lost prime and the first shot is not enough the pumps do not turn on till the crank shaft position sensor reads RPM and thus energizes the pumps again, this is the run mode. I hope I have given you some help. congrats on your newbe status I hope you have a great experience. JNT

Great idea! Plugged climate control line at manifold and got better rpm immediately! Having trouble with that ac anyway- we have mice and packrats and they can eat up wire and tubing.
Also plugged egr line and brake booster line- no change on those.
Where else can I lookfor vacuum leak?

This 91 300te just turned 325K and the adjustment tower has never been touched.
Thought I would rule out everything else first
Temp sensor
ovp
eha
o2 sensor
plugs, wires, dist,rotor
all test good or replaced.
The iac test fine with current, voltage, resistance.
Am going to make a manual with pipe hose and a ball valve to see what happens.
Thank you for the AV/heater direction!
Tom

What color is the plastic on the cold start valve/injector? I was told that the butterscotch color ones had problems on cold starts and were superceded by green ones. On a 90 300TE, changed it to green and it did start alot better; however, many other needed repairs were done at the same time so I can't say that it was definitely the sole problem with the cold start.

On my M103 the idle speed drops if I pull the plug.
Without power the valve is closed, well almost, there is an adjustment screw to hold it slightly open). If yo put some voltage on the connector it opens, with 12 volts it is fully open.

Rob

Interesting-
James Dean and just-ntime say idle increases when iac unplugged.
Me, Robpruijt, and johnflight1 have idle decreasing at 80c when unplugged.
I have measured current and voltage on mine in running engine and bench tested with 12v. All seems to be good.
Why are three of us (M103) getting the same results and opposed to the other two?

I think the immediate die on cold start is related more to the accumulator or check valves, but the car was just driven 500 miles away (with no problems except the start issue when cold = starts fine while using during the day with short (2 hour) stops) and won't be back till Tuesday.

Me too on the vacuum. Did the injector seals and orings.
Have you checked possibly fuel filter?
I was having problems with climate control so plugged the vacuum line that goes into the climate control vacuum control valve (trace the line from left of the brake master cylinder to the intake manifold ((at least on my 91 300te)).
Got a better and slightly higher idle with that plugged. So ther is a leak in the cabin.
Did not help the die on start issue at all.
Why the low idle with the functioning iac unplugged but working :confused:

anyone?

cold
 

My dead spot is at 1000-2000 rpm when cold.
It was not that long ago when I replaced the fuel filter and 1 pump because it sounded funny.
Based on what just n time said about the ICV rpm should go up to 1900 I am going to try another one from the local pick a part. although this one works fine when I hit it with 12 volts it opens right up. The reason I replaced it was the other one did not close all the way there is a small gap you can see light thru.,but it works fine when voltage is applied.
I have also replaced the ICV hoses, the one that goes to the bottom of the fuel inj unit keeps splitting.

This is a picture of 91 300te m103 idle air control valve off the car with no voltage applied.
I have heard that this gap is the normal stopping point of the valve.
And 12v opens it right up.
Is this what yours looks like? Please post your results if you get another iac and find changes.

The hose at the cold injector could be a problem area for me, but propane and carb cleaner in the area change nothing. Will look further.


Another question: When I unplug the iac (at temp) and the idle drops, plugging the iac (this is 2 pin unit) back in does not change this idle at all.
So idle still low until I turn off and restart engine.
Is this your experience?
Just trying to do diagnostics to solve this symptom.
Gracias

same
 

My original unit looked like that with a gap in the valve.The one in there now from the junk yard has no gap! I am going to put the original back in since it tests good electricaly.

Alright guys, I was mistaken. When I disconnected the IACV on my 190E 3.0, the idle dropped down lower. On my 420SEL it goes up to 1500rpm. I must have had them backwards. My apologies.

There should be a small adjustment screw to set the gap. It is sealed but can be freed.

Rob

ICV
 

Pulled the ICV and tested it. ops good and has the gap in the valve ,also rechecked the ICV hoses they are good still.
The old ICV I had laying around is inop electricaly dead.,I dont know why I save this stuff???
I did the ohm tests on the cap ,rotor,wires,and coil all that stuff cks good,but I may just do a tune up to rule out any ign problems and maybe throw a fuel filter at it.
Also yesterday I threw in a coolant temp sensor it is the one that mounts at the rear of the head it is two prong green on my 103.Lets see what happens:D

So original issue start die, low idle at first not the iac.
I replaced fuel filter, recent dist csap, rotor, nonresistor plugs, o2 sensor.
Tested the eha,
flow tested fuel volume(remove outlet connection on regulator, palstic tubing with hose clamp, minimum 1 liter/40 sec into plastic container),
tested temp sensor (4 prong on mine),
checked for vacuum leaks, replaced all small rubber connectors (not iac hoses)

Plan to check fuel pressure (need fittings), check valves at pumps,
check fuel accumulator this way:

Pinch off the 'return' from the accumulator and disconnect.
No fuel should should leak from the accumulator when you turn the key on, put a pan under just in case it's bad.
http://www.benzworld.org/forums/atta...fuelpumps1.jpg

What I can't figure out on mine:

Have someone start the engine (cold only, warm starts fine).
Airflow plate drops and immediately starts back up, engine dies.
If I hold airflow plate in position (do not let it rise), does not die.
Tryning to figure out that one.
Did you observe the airflow plate in yours at cold start?

Update-
Adjusted duty cycle through tower on the air/fuel unit. This cw adjustment seems to have done what I was doing manually on the airflow plate.
Had to drill and remove the anti tamper ball.
Running lean, enriched- huge difference at cold start.
Measuring voltage at X11, pins 2 and 3, 90 degree turn (small increments) voltage from .5v to 6.8v.

what about start problem?
 

Will the car start ok now? Is the problem gone with the car shutting off right after it fires up? My problem is worsening now! on acceleration I am getting detonation right where the dead spot is . Can my ign timing be off? maybe my timing chain is going bad? looked good when I did the valve stem seals...
I have also replaced the coil ,cap, rotor ,and cap cover the other day,No help
:confused:

Car starts ok now.
But you say you have detonation at dead spot and I do not know what you mean. Detonation into intake manifold or backfire? While driving?

knocking
 

It is knocking as if I put in cheap regular gas instead of premium gas. very poor acceleration. runs great at highway speeds but very poor performance from a standing start. I have tried different types of premium,Shell,chevron,ect....... no help

Have you used a voltmeter to check the duty cycle?
Real easy and will tell you if it is running rich or lean.

checked duty cycle
 

sorry took so long to reply been away for a while family emergency. I am planing to check the duty cycle again just for second guessing myself.
I thought it looked good when I checked it last.I am running out of parts to replace! I am following another post with a guy with a simillar problem now.

Hi everyone
300E 1990

When I unplug the cable of ICV, I don't notice any change in rpm, however when I detach the ECU cable rpm changes. But with the ICV unpluged, detaching ECU cable doesn't have any effect. Moreover while opening the switch a soud like "click" can clearly be heard from the ICV. So I don't really understand whether it is working or not?
Any guidance is highly appreciated.

Not a good idea to pinch rubber hoses with a hose clamp .Pinching hoses damage them inside as they are one of the oldest pats in your fuel system.

I was just thinking the same thing. I'm not a fan of pinching or clamping anything rubber, I'd rather put the open end in a container of some sort to catch whatever leaks out

My friend as been playing with his front brakes for ages now .Replaced all the items on front rh side .Only the flexi hoses are original . So replaced that and he cut it open to find the inside had closed up as it had been damaged by the hose clamp he had used. Hope you car sorted out soon.

Idle Air Control Valve help
 

Cold start very low idle and rough idle. Voltage to IACV 2.4v at operating temp.
Measured resistance of the IACV is zero. Replace the valve? Best source for new?

What range are you using for your ohmmeter? You should be using the lowest if not autoranging.
The resistance of the idle air control valve should be around 7.5 ohms.

I just went through testing the IACV again. With 12v direct the unit clicks. I did not remove to see if the valve goes full open. If I unplug the IACV the engine idle drops and stumbles. Remeasured the resistance and read 0 again. Cleaned the posts on the valve and read 8.4. Engine is running OK now. Also cleaned the air intake metering flap and that seems to help although it was not very dirty. Will post again after I try some more cold starts. Thanks for your input

If your resistance is reading 0 (dead short), you should be blowing fuses or burning up wires. Since smoke isn't rolling out of anything when you're applying 12V, I'd be looking at how you're measuring resistance or looking into getting a new meter...

Diseasel, you are correct. I was not making good contact with the valve pins. Cleaned them and read 8.4 ohms. I was thinking that I had an open circuit thereby not getting any resistance reading.

Spray all over the intake side with MAF cleaner or similar to check for vacuum leaks. Make sure to spray the injrctors. I had three pulling air past the seals. Check the IACV hoses for cracks and or brittleness. Replace the O2 sensor uf any doubt. If you smell fuel under the hood, check the EHA. If it's leaking, replace it and retune everything.

I had the dreaded low idle and found multiple problems. Huge vac leak where the injector body boot was not completely sealed was a big part of it, but it still dogged me until I put the O2 and EHA on it and spent an afternoon tweaking the EHA and mixture adjust. Car went from 18mph to almost 23 on the highway at 80mph. Averages just under 21 now in typical driving.

You can if you want to fix two wires to a bulb fix them on the iacv and take the wire and buld in to the car through the bulkhead , you can then view the operation of it with the bulb