Cleaning the throttle body to stop rough idle

[babyblueCE]

Hello all. I have recently changed my spark plugs and inspected the wiring loom and HT leads and all seems well but car still seems to idle rough some days and some days it doesn't. Does anyone know how i will access the throttle body on my C124 to clean it? I will also be changing the fuel filter as ive heard that sometimes these get clogged.

 

[coupe deville]

This " How to " is a throttle body rewire, you only need to get as far as the flap to clean it, is the car on the original engine wiring loom ?
http://www.w124performance.com/docs/mb/M104/M104_ETA_rewiring.pdf
not sure the 300 CE is exactly the same but should be a guide

 

[babyblueCE]

as far as i am aware the wiring loom is original, thanks for the link i will look into it!

 

[tintinmt]

A knowledgeable person recently advised me that similar symptoms were a result of the fuel injection system needing recalibration, but I dare say there are numerous possible causes for a rough idle. You might want to consider replacing distributor cap, plugs, leads etc if they are aged.

 

[hotrodder]

The 300/300-24 are very different beasts compared to the 280/320 with regards to engine management. The former use ke jetronic aka CIS (continuous injection system), when the later were introduced CIS was ditched in favour of HFM (hot film management) which is a distributorless fully electronic set up. This was also the time that the 'biodegradable' wiring looms were introduced.

Is there any pattern to the rough idle... any connection to running temp? Damp weather and/or after the car has sat unused for several days? Does the fuel tank pull a noticable vacuum (whoosing noise when removing the filler cap)? If damp/infrequent use ring a bell then i'd head straight for the distributor cap. If it doesn't ring a bell i'd still go there first but with slightly less confidence that it's the cause

 

[tintinmt]

Can I ask - What is the connection to the fuel tank vacuum?

 

[hotrodder]

The fuel tank is vented via a charcoal canister which feeds fumes to the engine under certain conditions. Not sure if the 300/300-24 are as sensitive to this as the later 280/320 but in those a fault in the regenerative evap valve can cause idle issues.

 

[carat 3.6]

The first thing to check on your car is the distributor cap, the m103 engine has an appetite for those. Next thing is vacumm leaks, with the engine running spray brake cleaner around any connections to the inlet manifold. If you hear the idle change you have a leak, use the brake cleaner to pinpoint the fault.

The throttle body is a bit harder to get at as it lives under the fuel metering unit. First undo the 3 nuts and remove the airbox. Next undo the 3 rubber mounts that hold the metering unit in place. Now undo the 6 pipes from the fuel injectors, and the pipes to the pressure regulator, cold start injector, and the wiring loom plug. Next undo the large clip on the rubber boot under the metering unit, and lift the metering unit off.

You now have access to the throttle body.

This is what has to come off.