C200 1997 Starts then dies when cold

[disclee]

About a month ago I noticed that the car wouldn't fast idle when cold. It'll start, go straight down to warm idle speed, then dies prob cos that's too slow. It's got such a state now that I have to keep the revs up (anything above 1500 would do) for a couple of minutes to warm a little and let go when it'll go down to about 700 and everything is well and good from then on.

I changed the plugs, cleaned the MAF and the looked at the insides of the throttle controller (motorised). That seems to work cos the throttle opens a fraction when cold. Apart from the MAF what could it be? I cannot find the over voltage relay.

Think the mixture isn't rich enough when cold starting.

 

[MondeoMan]

My first thought it the coolant temp sender, but I believe your car has a single sensor that feeds both the temp gauge and the engine management, so any failure should be obvious. Does it read OK - temp should be a touch above 80 degrees when warm?

 

[disclee]

Yes! A touch above 80 and a touch below 90 when in a traffic jam in summer.
Am tempted in changing the MAF but no one will 'lend' me one to try out. At £280 a try it's expensive.

I've read about the over voltage relay but try as I might I cannot find the big siver relay with a 10A fuse on top!

 

[MondeoMan]

I suspect the MAF too, but as you say it's expensive to replace on a hunch(though cheaper from GSF Car Parts - £172+vat). A diagnosis from a specialist is the way I'd go first, unless you're near Basingstoke - then you could try your sensor on my 96 C200 (assuming part numbers are the same).

 

[disclee]

Thanks a lot. The trouble is the car has to be very cold like overnight to exhibit the problem. I'm cleaning the MAF again. This time in a bath of IPA in an ultrasonic cleaner. Don't think it'll do any good.

 

[c320]

i think you should have it diagnosed and see what fault codes it brings up.

 

[disclee]

Success! - cleaned MAF

Finally cleaned the MAF by totally immersing it in IPA in an ultrasonic cleaner and the car's behaving impecably now. Acceleration is better, no pinking and starts first time.

Thanks to all who so kindly helped out.