W124 E320 engine idle problem

[mjcr666]

hi all,

having some problems with my E320 Coupe's engine.
when im at a set of traffic lights or come to a stand still, the engine runs lovely but as soon as you pull away the revs dip as if about to stall and then you drive off and all is ok, it only seems to do this when its up to temperature. i've had the air flow mass meter changed, glow plugs and ht leads to try and solve the problem but still the same which is very annoying.
I took my friend home tonight and he reckons the car is idling too low and may just need adjusting.

what do you think??

thanks
mike

 

[Tinkerer]

I think that it is a CDi but is it an auto or a manual? and what is the idle speed, loaded and unloaded??

 

[hotrodder]

W124 320 makes it the m104 petrol engine. Quite difficult to change the glow plugs on them , i'm thinking that was a typo

As said what is the actual idle speed in neutral/park and in gear (i'm assuming it's an auto as they nearly all are)? Is the idle rock steady or does it 'hunt' even slightly i.e. revs change by themselves? Did anyone check fault codes (read and clear, test drive and reread) before starting to replace things? Do you know if the engine wiring loom has been replaced/repaired? They are prone to rotting on these which can cause all sorts of problems in that a good sensor (air mass, temp etc) is potentially useless if the wiring to it is dodgy. Shorts in some areas like the feeds to the coils can ruin your day by taking out the ecu. There are also seemingly completely unrelated things that can cause strange idle behaviour like for example the fuel tank evaporative purge system. If you're paying someone to look at it it'd likely be cheaper and faster to use someone that knows these cars well

There is no idle speed adjustment, the ECU controls the throttle butterfly for idle speed and (if fitted) cruise control. If it's just idling too slow something as simple as cleaning the throttle butterfly could be all that's needed or at least improve things. Worth doing as it's a very simple and quick job... remove the air trunking between the air filter and throttle body (a few clips, a couple of nuts securing it to the rocker cover and a couple of sensors) and then you can see the butterfly and get to it with an old toothbrush and some brake cleaner