124 - 300te hunting at idle?

[brucemillar]

Well a good 100 mile run this afternoon with no dramas.

The engine hunts badly at idle only when very hot.

I am suspicious of the twin pipes on the idle control valve. I know both are split where they push into the actual valve. These have seen a previous repair with jubilee clips. I have bought new pipes and will replace both.

Q. Does the inlet manifold have to come off to get access? It looks like I won't be able to get my hands in to push them home or remove the longer pipe?

Taking off the manifold looks like a faff. Loads of small metal pipes.

Sent from my iPhone using MBClub UK

Sent from my iPhone using MBClub UK

 

[grober]

ONE SUGGESTED WAY TO TEST
Firstly, you’ll want to have your engine at operating temperature for this test. Vacuum leaks should be more pronounced when doing this simple test, spraying a little starting fluid or brake cleaner around vacuum components with the engine running. If you have a vacuum leak, the engine will run completely differently when it sucks in the starting fluid. It’ll “rev up” and you’ll more than likely have found your vacuum leak and your high idle. Celebrate! Just be careful when you're doing this and shoot in short bursts. Nobody wants you to blow up.

 

[brucemillar]

Cheers Graeme. Would you expect this to work on the idle control valve?

Sent from my iPhone using MBClub UK

 

[Charles Morgan]

All the idle control valve does is provide air to the inlet manifold in larger or lesser quantities at idle when the throttle butterfly is shut. So if the hose is leaking Graeme's test will work there too.

 

[brucemillar]

Okay

I removed the air box today:

Let the engine run at idle until she reached reasonable temp 80c+ at this point (as is normal now) she starts to hunt.

So with the air box removed I sprayed all the vac lines, Idle Control Valve, and plenum with Damp Start. This made absolutely zero difference to the hunting.

I am thinking this shows that I do not have a vac leak? I did spray all over the right hand side of the engine with zero difference to the hunting.


I have read that the engine temp sender can cause hunting when the engine gets hot? This is then sender that sends to the ECU. Does this sound reasonable?

Can anybody tell me where it is located (pics if you have them please).

Many hanks.

Bruce

 

[grober]

Not sure if damp start will do the trick. Starting fluid or brake cleaner will look like "fuel" to the engine as it will be mainly flammable hydrocarbon Damp start may be an inert water dispersant rather than "fuel" so may not be suitable

 

[brucemillar]

Dammit. I went bought the damp especially for this. I figured it was alcohol based so would do the trick really well. Back to the drawing board.

I now need to hope for rain or somebody who wants a nearly full can of damp start ;ˆ)

 

[brucemillar]

Okay. My bad. What I used was - Bradex Easy Start - This is labelled as "Highly Flammable" Spray into air intake with engine off wait 10 seconds then crank!! So would this be Okay to test for vac leaks?

 

[grober]

Okay. My bad. What I used was - Bradex Easy Start - This is labelled as "Highly Flammable" Spray into air intake with engine off wait 10 seconds then crank!! So would this be Okay to test for vac leaks?

BRADEX Easy Start should show up any intake leaks if that's what you used .

 

[grober]

Okay. My bad. What I used was - Bradex Easy Start - This is labelled as "Highly Flammable" Spray into air intake with engine off wait 10 seconds then crank!! So would this be Okay to test for vac leaks?

BRADEX Easy Start should show up any intake leaks.

http://www.partinfo.co.uk/files/BES1A Bradex Easy Start MSDS.pdf

 

[brucemillar]

Cheers Graeme

Bradex is what I used. Any thoughts on the Temp Sender causing the hunting?

 

[grober]

In theory if the engine temperature sender was telling the engine ECU the engine was cold it would richen the mixture via the EHA among other things. This might cause an uneven idle. This might be detected by measuring the air fuel ratio at the exhaust which should lean down as the engine warms up. Might also be worth pulling a sprak plug or two to see if they show signs of running rich? There are two engine temperature senders 1. gives a readout SIGNAL for the temperature gauge 2. sends the engine temperature to the ECU.

help were is the temp sensor that causes cold start issues - PeachParts Mercedes ShopForum

IRRC the temperature sensor is the NTC [ negative temperature coeffficient type] in other words its resistance should go down as the engine temperature goes up. Haven't any test readings to hand sorry.