W203 C200 Cdi issues...been on STAR..need advice?

[Jamielan84]

So firstly the car is a 2005 C200 Cdi auto with 88000 miles and full MB History.
I brought the car 2 weeks ago, private seller who had the car 6 years, was last serviced 1k mile ago at main dealer.
Test drove the car from cold for a good 15 mins and drove perfectly, noticed the temp gauge had moved only a mm or 2 within that time but being diesel they take a while to warm up anyways and looking at the condition and history of the car I drove it home. The drive home was all motorway and the car came up to temp after about 20 mins of driving and all was well...until I came off the motorway and noticed the car was almost hunting or surging within the 1500-2000k rev range between 30 and 40 mph and anything over that it drove fine.
I took it out the next day and it drove fine apart from taking a while to get to temp again but as soon as the car was warm I had this surging again.
Had it on my own diagnostics and all live data was within tolerance and couldn't see any issues whatsoever, did a leak off test and injectors are fine.
with MAF being common on these cars I opted to try a Bosch MAF...no difference. Opted for a Bosch Lamda sensor..no difference, took out and cleaned EGR and tested it..no probs, did a DPF regeneration and replaced bosch back pressure sensor..no different.
Been using it for work as it is and from cold I can get nearly 50mpg (that's at 70mph on cruise for 40 miles) yet on the same roads at the same speed I may only get low 30s sometimes.
Anyway I had time today to get it to a merc specialist and leave it with them to get it on star and see what they think. All data came back fine apart from a glitch in the low boost pressure...which star then asks to do a leak test which the car passed along with actuator function etc
Advised...possible new turbo
I don't like shelling out turbo money on possibilities so I have come here to get some opinions really, has anyone came across anything like this before?
I just don't understand why the car behaves itself from cold...surely if the turbo had issues it would be constant?
Any opinions would be great thanks in advance

 

[AMGeed]

If the engine is not coming up to 85c+ then I'd start with replacing the thermostat.
A cool running car will be more thirsty too.

 

[mbenz1]

Hi and welcome to the forum.

Regarding the warm - up time issue: In this weather the car should be on or above the 80C temperature mark in stop/start soft/medium - right foot conditions @ 15 minutes. If no traffic then even quicker to warm up. I suspect your thermostat needs changing as I had same warm up issue on our 2005 C220 CDI. Very common for thermostat to slowly wear on this engine and not hard to change.

Regarding the hunting/surging at specified rpms - do you have the fault code to give for the boost pressure fault?

I've experienced this on the C220 cdi and error was "boost pressure too high" and STAR shows all as Good so no definite answer to this issue.

Have you experienced power loss also?

I think this boost issue is either caused by the internal vanes in the turbo sticking due to carbon build up or a dirty EGR valve, if STAR is not pointing out any specific fault codes.

Sent from my GT-I9505 using MBClub UK

 

[Jamielan84]

Thanks for the replys, I gathered the stat was not working properly which I will replace if I get to the bottom of this running issue.
The report for boost pressure is the only thing that flagged up with star....specified values should be 1038-1088 hpa and the actual value was 1009hpa going off the report in front of me. Only actual fault code showing on diagnosis was a problem with the heater booster which I am told is always a fault on this model (I usually only have petrol mercs so diesel are new to me) and not to worry as this isn't part of my running issue...

 

[Jamielan84]

And sorry just to add...no power loss? car drives fine and seems to boost fine and drives ok after the 2k rpm mark...kickdown works fine and the car will easily accelerate to over 100mph and keep going

 

[mbenz1]

If you're symptoms are intermittent occur very occasionally then I personally wouldn't be too worried but to keep an eye on the net / this forum if someone can suggest a fix to this boost issue. See how you get on and let us know if problem returns.

On the other hand, Have you tried some good quality injector cleaner additive or Shell Ultimate fuel and a good run? Highly recommended for a diesel as these engines clog up a lot. I use an additive every 3-5 months and take the car for a spin on the motorway to keep things clean...

I have had a thought in my mind for a while now which is to use some turbo charger spray cleaner which is sprayed into the air intake whilst the engine is running to clear the turbo but I've just not had the time to look into this as I don't want to be damaging anything at the same time.

Sent from my GT-I9505 using MBClub UK

 

[bob6600]

+1 for replacing thermostat

Did a 2005 W203 have DPF?

 

[mbenz1]

+1 for replacing thermostat

Did a 2005 W203 have DPF?

Good point. Definitely not standard on this engine but was available as an option.

Sent from my GT-I9505 using MBClub UK

 

[a111r]

I have had a thought in my mind for a while now which is to use some turbo charger spray cleaner which is sprayed into the air intake whilst the engine is running to clear the turbo but I've just not had the time to look into this as I don't want to be damaging anything at the same time.

Sent from my GT-I9505 using MBClub UK

I don't buy the concept. Volatile Organics, which is what all these cleaners are, will simply burn, once combusted, and so I can't see them having any cleaning action on 'accrued carbon' in the hot VNT side.

The 'quick 'n' dirty' "Mr Muscle" method may work if you can disconnect the EGR pipe joint and then flush it out.
Better all round is to remove the turbo, dismantle it, and manually clean out the VNT, with the proviso that ... any wear in the vane interface will clog up again.

 

[Jamielan84]

Deffo a dpf model. Thermostat isnt a problem at the moment...i only mentioned this because the car takes a while to heat up and the problem isnt visible on test drive from cold.
Spoke to indie today and he thinks sticky turbo vanes at low rpm once turbo has got hot...he has seen this before. Can only advise me its that tho so question is...do i throw a new turbo at it and do i offload it. Or do i remove turbo and take a look at it? ..but if its only playing up when warm...inspections not going to give much away i guess?