HELP! 300E, cruise control problem

[steve437]

300E 1988, 170,000 miles.
Can any one suggest a fix for my cruise control? Accelerates evenly to any set speed then is constantly on - off the throttle maintaining the set speed. Giving a very uneven feel to the ride. If I hold the car on the foot pedal at any set speed it's smooth. The only other minor problem is with cold starting when left overnight, the car starts rough at 500 rpm and is prone to stall. When warm it starts correctly, rev's to about 1,000 rpm and settles to 750 rpm.
Two merc, main dealers have had the vehicle for a week each. Changed all 6 injectors, new throttle control valve and head off for a sticking exhaust valve that didn't. Plenty of bills but no cure.

 

[sebastianforbes]

hi there

all that i can suggest for the rough startup is to hold the key longer (starter motor) for the engine to get a better rhythm - it's what i do for my '89 300te.

cheers

sebastian.

 

[Arnie]

Many of the 300E (M103) engines have this cold-start "problem". If the injectors, accumulator, pump, aux air-valve, cold-start injector, OVP relay, etc etc are all ok, and they invariably are, ...then either adding a 450 ohm resitor to the temp sensor to enrich the mixture (by making the ECU think it's a bit colder than it really is) during warm-up, or adjusting the mixture-adjustment screw (tamper-proofed and adjustable replacment part from MB required) may be the route to go.

If your car used to start OK and this is a new occurrance, then check all the usual things again, including, ignition leads, distributer-cap, rotor etc..If not, try the above.

For the Tempomat cruise control, see here:

http://f1.parsimony.net/forum1221/messages/3200.htm

 

[steve437]

Thank you, Sebastian & Arnie, for your suggestions. I waited to respond hoping for good news, but!! I put car into J Russells (mb)at Downham Market for the problems. As I am driving down to Spain shortly, I did not need the grief. A waste of time and money that was, I asked them to cure:- cruise control and starting fault and inspect the car. They found the faults but were not sure what was causing them. Said the car was mechanically fine apart from a crack in the exhaust. £135 lighter, I decided to change the cruise actuator and cpu, after being assured that " no way is it the speed sensor" now I have no cruise control at all. I did however find a broken spring on the front off side(w**k*rs).
I've a feeling that when I was testing the actuator from the cpu 14 pin plug I may have sent some juice down another circuit and blown something. I did have a relay clicking, as I searched for the correct wires that activated the actuator, which I replaced. I would be grateful if anyone can suggest other places to look.
The starting fault I cured by removing the brass disc under the air intake and cleaning the throttle butterfly valve chamber with petrol and an old tooth brush this picked the rev's up considerably, and I had to readjust the throttle slightly, but sometime ago I had adjusted the throttle linkage to maintain tickover, this took everything back to it's original settings.
I had a flexi-hose in the engine bay, coming from the tank to the injector pump, that was not air tight. I assume fuel was running back towards the tank overnight. I cut an inch off and reconnected with a jubilee clip, this cured the need to spin the engine more than once or twice before firing. I asked J russells(mb) to replace this while they had the vehicle. A hose that didn't fit the vehicle was left in my boot, and another £17 added to the bill, which they will be gettting back tomorrow. Top service!
Regards Steve437