M103 2.6 Idle Issue

Steve260E

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My m103 2.6 has had an idle issue ever since I have owned the car, it always eventually starts but it is a bit touch and go when its really cold outside.

Basically the fuel pump will prime, turn the key and it initially fires for about a second and die, cranking and cranking it will then catch and idle at about 450-500rpm, obviously if you go near Drive or Reverse at this point it will just stall, I have learned to feather the throttle for about 2 minutes and idle it myself at about 1500rpm and once up to a decent temperature the idle will sit comfortably at about 750-800rpm and at this stage it is perfectly drivable.

I have checked the OVP and this seems new, took out the cold start injector and gave it a clean and it seemed all OK, fuel was present in the lines up to it anyway. However the Idle air control valve was disconnected, connected it up and the idle shot up to a constant 1500rpm even when warm, as you can imagine the thing wanted to shoot off in Drive or Reverse so this is not usable.

The problem only exists when cold, when warm it starts up on the button.

Does anyone have any advice as to what I can do to pin point the problem?, since the IACV was disconnected by a previous owner I tend to think that is the problem, the small valve inside stays open by about 5mm when disconnected and when you connect it up with the ignition on the valve will operate and shoot open fully.
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optimusprime

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There is a test for the ACV valve .You know the economy gauge in the speedo head where is the needle at tick over.? Check small vacuum pipes and rubber ellbows joints.
You need to look at all the fuses and earth points even on the battery .
But dont take the possitive or negitive wires off , thats if you dont have the code for radio. These are just maintenance jobs to do but once done you can go on to the next step.
 

optimusprime

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Steve the cold start injector needs information from the engine temperature sensor ,its the last one on the top right of emgine see picture. Look at it and make sure its making good contact . .You might have the two pinn one or the round 4 rin . The one in the picture is like mine two pin .
 
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Steve260E

Steve260E

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Thanks a lot for your advice and also thanks for your PM, I have saved that and will have a good look at it, I will take a closer look at the temp sensor, mine is the 4 pin plug and as you say my cold start injector might not be getting any info from the sensor if it has gone bad, meaning that even though there was fuel sitting in the lines up to the injector and it was under moderate pressure it might not actually be getting pre injected into the manifold when its needed for cold starts.
 

Charles Morgan

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If it's revving at 1500 with the ICV connected it will not be the cold start injector. It is getting more than ample fuelling.

If the ICV is remaining fully open despite reaching operating temperature my money is on it being faulty or it getting duff info (which gets into a whole world of other options). I'd start with the ICV, check the wiring is properly connected and check the voltages being sent to it. They get gummed up with age as well.
 
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Steve260E

Steve260E

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I should point out that when I checked the operation of the ICV i.e by plugging the thing in while the engine was running, it was probably up to a decent temperature at that point, I imagine a better test would be to plug it in from cold start and see how that is.

I suppose it would be worth taking out the cold start injector again and seeing if it actually fires into a bowl from cold as well, thanks for your advice, I will check the voltage being sent to it and give it a soak in some cleaner.
 

stwat

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These can suffer from broken wires to the temp sender. I've had this on two of my M103 engined mercs. You can buy new connectors from merc. They come with a good leanth of wire attached so you can trace any breaks quite far back into the loom.

There is a micro switch on the throttle linkage that can go bad. Also the throttle cable can be misadjusted causing the switch not to be clicked when throttle released.
 

190

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If the idle air control valve is the same type as on my 190e they are adjustable. It had a bimetallic strip that operated a moving quadrant which opened to allow an idle air bypass when cold. A combination of engine heat and an internal electrical heater closed the valve as the engined warmed up. There was a small lock nut that could be slacken off to make the adjustment and that would change the cold idle speed.

I might be talking rubbish as by 91 your engine will have had a cat but that's how it worked on my 89 model.
 
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Steve260E

Steve260E

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Thought I would give a quick update, plugged in the ICV from cold this morning and it started perfectly and idles about right for a cold engine, only as the engine warmed up the revs increased to about 1700rpm at idle.

Took a quick voltage measurement at the plug to the ICV and it was reading 13.8v and steadily increasing as the temperature rose, surely that's not right? Anyone any ideas on that?

On the plus side I changed all the plugs which were a mix match of all different types for NGK BP6EFS, fitted a new rotor arm and tightened up the throttle cable and the improvements already are massive. Just this pesky start up issue now.
 

optimusprime

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If the idle air control valve is the same type as on my 190e they are adjustable. It had a bimetallic strip that operated a moving quadrant which opened to allow an idle air bypass when cold. A combination of engine heat and an internal electrical heater closed the valve as the engined warmed up. There was a small lock nut that could be slacken off to make the adjustment and that would change the cold idle speed.

I might be talking rubbish as by 91 your engine will have had a cat but that's how it worked on my 89 model.
none adjustable .
 

optimusprime

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Steve your working wrong . Pull off the plug on the rear of acv .Wait till its cold like next day .Spin it over at cold .You should find it running at 1500 revs .If not remove the ACV from the engine ,only 2 screws thriugh a saddle . But dont pull the hoses off the engine side or they will be hard to get back in place if you do. In the garage fill it up with white spirits .Let it stand for 1 hour ,shake it up ,tip out the crud.Refit it Look at the rubber hoses on the rear for splits .If all fine fit it back in place .Then return let ius know how it is.
 
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Steve260E

Steve260E

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Since I have owned the car the plug has always been disconnected from the ICV, I only noticed this recently when I investigated due to the cold weather the previous owner must of done this to combat the high idle issue when it is connected.

Without the ICV connected i.e the way it has been since I bought it, the car would struggle to start and idle at 450-500rpm from cold. When connecting the ICV at cold the car starts better but the idle rises steadily to 1500-1700rpm when warm so is unusable.

So to summarize:

With ICV connected: 1700RPM idle

Without ICV connected: 450-500RPM idle

I have removed the ICV and gave it a quick rinse with WD40 but nothing as intense as you suggested with white spirits but I will try that tomorrow and report back.

I tend to think however that the high voltage reading at the plug that connects to the ICV could be part of the problem, should the connector be reading almost 14v?

Cheers
Steve
 
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optimusprime

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Steve can you Google this ? and in the search box put -
89 300E W124 M103 High Idle Solved
Then look at the first post from Peach Parts ,look for High Idle Solved . It is looking like the temp sensor . Let us know how you get on .
 
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Steve260E

Steve260E

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Indeed I have read that post a few times, I have searched many threads on many different forums and it seems the problem is always something different!

Having said that I had a new Delphi temp sensor delivered this morning so I will fit that and report back how I get on.

thanks again
Steve
 
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Steve260E

Steve260E

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Quick update, changed temperature sensor and the issue remains.

With idle control valve connected I get 1900rpm idle, without it connected it struggles to start and idles at 450-500rpm warming to a steady 800ish-rpm. Still haven't given it a clean out in white spirits but thinking could be a bad o2 sensor?

I must say however that since changing the plugs and the rotor arm it starts much much easier but still not as it should be.
 

optimusprime

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Steve i must be a bad vacuum leak .You must clean the acv out its a happy medium your after .Just clean it out and thats finished with You can check the ACV after you get it off Did you spray starter fluid on to the rubber boot thats under the metering unit?? If it split it will suck in fluid and make a change to the engine revs.
 
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Steve260E

Steve260E

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I will give the valve a clean out before I try anything else when I get a chance, its not a daily driver so not in any rush to sort the problem, that's a good point about possible split rubber or even gaskets, I will try that and let you know how it goes. Thanks for all your advice
 

stwat

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Have you checked for broken wires yet?

I have had to replace them on 2 of my 190's and my 126 had had them replaced before I bought the car.
 

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