Engine stops when driving slow

[JimH]

300 SL 1991 65k miles.M103 engine. Runs fine at speed but engine stops when slowing down or driving slowly i.e. in estate with speed bumps or joining roundabout. Any ideas?

 

[EmilysDad]

does your car have an idle air control valve? They cause idling problems when they stick

 

[LostKiwi]

https://www.benzworld.org/threads/k-jetronic-troubleshooting-flowsheet.1222938/

This might help.

 

[JimH]

does your car have an idle air control valve? They cause idling problems when they stick

Thanks. Don’t know but will check if I can find it.

 

[JimH]

https://www.benzworld.org/threads/k-jetronic-troubleshooting-flowsheet.1222938/

This might help.

Thanks. I’ll work through this.

 

[EmilysDad]

Thanks. Don’t know but will check if I can find it.

They control air flow around the throttle butterfly

 

[ajlsl600]

Vac pipe off. Leaking?

 

[LostKiwi]

Vac pipe off. Leaking?

Goid call. Engine goes excessively lean on closed throttle due to leak.

 

[ajlsl600]

Goid call. Engine goes excessively lean on closed throttle due to leak.

Start with wots simple.

 

[JimH]

Thank you all. Don’t see any leaks but will check again.Vac iis definitely connected.

 

[LostKiwi]

Thank you all. Don’t see any leaks but will check again.Vac iis definitely connected.

There is a vacuum line goes from rear of inlet manifold to the vacuum manifold in the module coffin (passenger side, under bonnet just in front of windscreen). The manifold can split and leak. A quick check is to operate the heater vents control to see if the air can be directed anywhere other than screen and side vents.

 

[EmilysDad]

Thank you all. Don’t see any leaks but will check again.Vac iis definitely connected.

Carb or brake cleaner sprayed around any vacuum leaks should see an increase in revs

 

[star]

Clean the throttle butterfly and then check the Co2 settings.

 

[JimH]

Thank you all for your help. At the moment I’m stuck getting the air filter cover off. That’s the stage I’m at! As far as driving the car, I’m moving into neutral as I approach junctions and starting off in first gear. Funny way to use an automatic gearbox but it prevents stalling just now till my motor engineer is back in business after lockdown.

 

[malcolm E53 AMG]

Does this engine/year have a distributor/rotor arm or is it electronic? If it has it will likely need replacing due to hairline cracks and condensation my 88 plate 300te suffered from this - new distributor cap and rotor solved the problem

 

[JimH]

Yes my M103 engine has a distributor. I think it was serviced within the last year but I’ll get the mechanics to check it again. Thanks all for your comments.

 

[malcolm E53 AMG]

Yes my M103 engine has a distributor. I think it was serviced within the last year but I’ll get the mechanics to check it again. Thanks all for your comments.

My local garage were scratching their heads on this one and couldn’t find the problem and eventually it had to go into a MB franchise and they sorted it by fitting a new distributor cap and rotor arm - obviously a known problem with moisture building up in the cap on start-up and the cutting out would occur circa 2-3 miles into the journey - leave the car for 25mins and it would start again as the moisture evaporated from the residual heat in the engine

 

[LostKiwi]

Same problem on the m119 V8s too.
On them the cure is to smear the back of the bakelite cup at the base of the distributor with silicone grease. A light smear on the cap as well and they behave perfectly.

 

[JimH]

When my engine stalls I can restart it straight away. The problem is stalling at all! Feels like too much fuel intake when reducing revs to idle level. Also needs nursing when moving off from a standstill. Thanks for all offering help

 

[malcolm E53 AMG]

I might be wrong but isn’t there an electronic control device sat with the main ECU that stops the tickover dropping too low on automatic cars to solve the problem of stalling on take-off