Rough Idle, Hard Starting

SuperHans

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Hello all! I recently got a 2004 c270 cdi w203 (facelift) for a good price knowing that it needed some work doing to it. I love the car by the way, far more refined that my 1.9 TDI previously!

I've diagnosed a thermostat problem since it only reaches 60 degress on a 120 mile motorway journey. I will be replacing that very soon.

However I also have a problem with a rough/fluctuating idle and some issues with starting the engine. The engine doesn't start from the first turn of the key, it takes around 2 to 4 cranks to start.

I'm assuming that these issues are interlinked and to do with either slightly leaky injectors or corroded fuel lines/o rings. I realise they're not major but I'm hoping that I've caught the problem before it gets big! Hopefully given my minor symptoms and the fact that I have 2 simultaneously one of you guys will know what it is instantly. So what do you think?

Any tips on getting the lines off?

Thanks a lot!
 

WG M-B

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It sounds very much like the fuel lines are letting in air. I'd advise to change all the lines and not just the o rings
 
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SuperHans

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It sounds very much like the fuel lines are letting in air. I'd advise to change all the lines and not just the o rings

Very interesting that you say that instead of just the o rings, what makes you think it's the fuel lines themselves?
Thanks for your reply
 

dhk284

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Hi it could also be the MASS Air flow or induction pipes, mine is petrol but same as you hard to start and rough idling, it worked for me but try the O-rings first.

Rgds Derick.
 

BlackC55

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SuperHans said:
Very interesting that you say that instead of just the o rings, what makes you think it's the fuel lines themselves? Thanks for your reply

The lines get brittle over time.
 
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SuperHans

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Those air lines are damn hard to get off! Am going to have to devote a day to it I think, just to ensure I break nothing. Tried again this morning but they're just not budging and I'm worried about breaking them. Any tips?
 

BlackC55

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Have you got the new pipes?

To remove them. Push the top clip (white) so the tabs splay out. Push the top of the connector so it enables you to put a very small screwdriver between the connector and the metal body you are removing the pipe from.

It's like opening a bottle of beer.
 
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SuperHans

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Have you got the new pipes?

To remove them. Push the top clip (white) so the tabs splay out. Push the top of the connector so it enables you to put a very small screwdriver between the connector and the metal body you are removing the pipe from.

It's like opening a bottle of beer.
Great, thanks for that tip, I will try again later. No I haven't bought a set of new pipes yet, I want to try the cheap things first, I also can't see any air in the pipes when the car is running so I'm assuming it's not a major problem (I'd trust your opinion over mine though ofc!). There's only one small air bubble in the pipe and it's when the car is switched off, it's on the pipe from the pump to the filter, about 2cm from the end of the hose end at the filter.
 
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SuperHans

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Apr 30, 2016
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c270 cdi
Have you got the new pipes?

To remove them. Push the top clip (white) so the tabs splay out. Push the top of the connector so it enables you to put a very small screwdriver between the connector and the metal body you are removing the pipe from.

It's like opening a bottle of beer.
I changed 4 of the o rings today, the one by the fuel filter, the rail and the 2 on the fuel pump. It seems to be slightly better now and there are no bubbles when it is idling. However, when I put my foot down I can see some bubbles in the fuel line by the fuel filter - so perhaps it is air in the pipes that has been causing the trouble all along. Now, the air is only visible in this fuel line, I can't see it in the transparent one on the fuel pump (the one not connected to the fuel filter). Sooooo does this now point to exactly what line needs changing? Which one do you suggest? Thanks!
 

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