2005 C220 cdi going into limp mode

[Brozzer]

My 220cdi with 110k miles has been going into a limp mode (reduced power, won't rev over 3K and won't kick down) over the past 6 months and has been getting progressively worse and more often.
Originally it would only do it after a long run on a motorway but now does it more than runs correctly.
When it is running ok it runs perfectly with no smoke, plenty of power and no issues.
Sometimes you can start the car and in park it will rev freely to over 3k 3-4 times then won't rev above 3k.

I just had a full system code scan with a Star Diagnostic tool at a local MB specialist.
The only codes that came up were:

2509 -check component N33/2 heater booster control module
2135 - glow plug cylinder 3

I was told that that my car doesn't have a heater booster as it was only fitted for cold climates so is a "red herring" and the glow plug wouldn't cause a limp mode.

I was advised to check the swirl flaps and actuator if fitted - my car does not have swirl flaps.
Did a leak off test on the injectors - all good and equal.
It's a pre DPF model.
EGR is fine.
Turbo actuator moves ok
Checked turbo hosing for oily blow marks and boos pressure is good on live data.
Fuel rail pressure is good and steady on live data.
New battery fitted and charging at 14.5v

Any ideas anyone?

 

[rf065]

My CLK 220CDi had the same problem & got progressively worse with no fault codes either. Turned out to be a split intercooler hose.

 

[Brozzer]

Did yours go into limp mode even revving the car whilst stationary?
Maybe ill just pull the front bumper off and take the intercooler and pipe work out to check it all.

 

[rf065]

Yes, it started on the m/ways only at first, then got worse over a two year period. It never showed any codes, just went to limp mode & after restarting it would run perfect again. After two years of getting worse, it finally threw up the engine management light and a code relating to boost pressure. That was the only time a code was ever shown, new hose & it never went into limp again.

 

[cws196]

Ditto on intercooler hose-had the same on my previous C220.

 

[Brozzer]

I removed all of the turbo hosing and intercooler and pressure tested it... no leaks. I then refitted and smoke tested the whole system... no leaks. So have now ruled that out.

 

[Brozzer]

Finally figured it out... the EGR valve was occasionally not sealing correctly.