C240 - Starts fine, then power drops, then fine

[michaelarran]

1998 C240 Sport (65k miles, petrol, auto) - new air sensor fitted in Spring.

Starting from cold is perfect (1200rpm idle), and the car pulls away OK, though feeling a little uneven at times if I accelerate hard. If I then stop at a junction before it is up to normal operating temperature (about 80 degrees), the revs have dropped to about 700, and if I try to pull away from standing nothing happens for a few seconds, and then suddenly the power comes on. To my unskilled mind it feels as though the choke has cut out too early - but I have no idea if the car even has such a thing!

Once up to normal temperature, runs like a charm.

Any ideas, please, as I am looking to sell it, but won't do so unless I am happy it is running properly.

Thanks

Mike

 

[anyweb]

have you tried the obvious ?

spark plugs, oil, oil filter and air filter, plus if the problem is still there the fuel filter/fuel pump.

of course someone might mention the crankshaft sensor, it may be worth looking at.

just a thought, cheers
anyweb

 

[television]

Dont think crankshaft sensor as the engines stop when this goes, could it be just a simple sensor like the water temp or air temp, they should both measure around 5k- 7k ohms when cold, just pulling the wire off would prove the point

 

[BlackC55]

Air mass is where my money is.

 

[television]

Air mass is where my money is.

I did not say it though it crossed my mind as the car is OK when warm

 

[BlackC55]

I bet its not under hard acceleration.

 

[television]

I bet its not under hard acceleration.

Thank you

 

[michaelarran]

Hmm BlackC55, may have to pop in and have you take a look, as I'm just the other side of Butser. Will be next week, as I'm maxxed out in the office, then have the Petersfield fireworks to help run over the weekend.

Wedglen Garage, Midhurst, replaced the air mass sensor a few months back - tried several Bosch ones before they fixed the other problems it was having (wouldn't change up a gear under hard acceleration, until I lifted my foot off the pedal and no power from a cold start - OEM parts fixed the former, but not the latter), then put in an official Mercedes part, which seemed to do the trick.

Cheers

Mike

 

[BlackC55]

I think I have been on the phone to the midhurst garage about your car.

See you soon

 

[michaelarran]

No problem with hard acceleration when warmed up.

From cold it starts fine, and pulls away, but a slightly unevenly - I noticed the revs dropping about 100 for a second or so.

Once warmed up though, goes like a charm either from standing, or kicking down.

 

[michaelarran]

It seems revs related. When I press the accelerator the revs drop, and it feels like it is close to stalling. As soon as I lift the pedal the revs come up and I can pull away smoothly.

Odd!

 

[wolly]

wolly

i had the same problem with my c240.
check your fuel pump relay make sure it is in properly inserted if all seems well switch it with another relay and see how it drives for a few days if problem disappears change relay

other causes maybe
maf