R107 hunting tick over

[tomadaly]

I have a 1973 450SL - R107 - V8 auto with 135k miles
Recently when started from cold the tick over hunts between 800 and 1500 rpm - rising and droping - like I was slowly reving and easing off the trottle - this keeps going and slowly reduces as the engine heats up - when warm it ticks over normally about 800rpm. Any ideas

 

[television]

Hunting is nearly always an air leak on the inlet manifold.

The max vacuum is at idle, so the engine is sucking at its max, with a cracked a badly fitting pipe on the inlet somewhere the engine will suck in air from that leak, so the engine speeds up, as it speeds up the vacuum goes down, and the engine drops back to idle, and so the cycle continues.

Check the pipes first

http://www.detali.ru/cat/oem_mb2.as...&L=765.701&CT=F&cat=048&SID=80&SGR=015&SGN=01

The vacuum pipes end in a bunch in the passenger side near the bulk head, normally blue the split and leak

Last and not least, welcome to the MB forum

 

[tomadaly]

thanks Malcolm

I was going to start looking at the electronic ignition - looks like you saved me a lot of wasted effort - there seems to be lots of pipes to check and I hope I don’t have to take too much apart - I assume best place to start is at the Carb and work out from there.

I've looked through the forums on a regular basis - but this was my first posting and I'm amazed at the quick and useful response - thanks again.

 

[television]

There is a whole pile of T pieces in the engine compartment rear right up near the ifre wall and it is always worth changing those when standing at the front and they all leak after some year. Another point is the pipes on the rear of the headlamps, that come off.

Once all of these pipes are sorted and checked you will find the central locking much better as well.

When I first replied I did not know if the car was injection or carb, but being a carb it confirms the above

 

[tomadaly]

now i'm confused

it is fuel injected (i had to replace some of the small hoses last year) but under the air filter - there is what I assumed was some form of cab - linkages from the trottle - does that chage your suggested leak hunting sequence.

 

[television]

it is fuel injected (i had to replace some of the small hoses last year) but under the air filter - there is what I assumed was some form of cab - linkages from the trottle - does that chage your suggested leak hunting sequence.

No not at all :grin: