OP - I had nearly identical experience with an SDL I picked up March'13. My input in red:
Quote:
Originally Posted by i_amnt
I have found a couple threads about this issue, but all of them either do not really match my symptoms nor come to a helpful conclusion. This is about my 1985 300TD Turbo. Same result here after searching for like experiences from others with an '86SDL (both cars have similar emissions setups.)
I have been having a loud distinct whistling at certain rpm. It doesn't coincide with the engine speed.Wait wut? It is most distinct at third and fourth gear.After establishing cruising speed (not accelerating, less road/engine noise) As it gets louder, it seems to take some power away and slows the car a little.Almost imperceptible Or, if I let off the gas a little, it will also become louder.MOMENTARILY It will get louder and the car becomes slower (maybe 5 mph slower, typically) until I push down on the accelerator and the whistle silences and it feels like the turbo really spools up and the rpm increases and off I go with a bit of power. If I stay cruising a ~65 mph, then it never happens. But, at around 45-50 mph, it gets very annoying.By design the ARV works within a set RPM range, I'm not 100% but it's something like 1800-3k
The previous owner told me it was a vacuum leak, other similar threads seemed to propose it was an intake/exhaust leak. Something else I just read talked about bypassing the EGR, maybe there could be a leak there?
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Here's the skinny. It is a leak and is also dependent on engine rpm. That loud whistling is coming from the ARV valve on the turbo as result of a weakened spring that opens now merely from boost pressure.
- Verify you have the ARV wart on the compressor housing (if not, we done!)
- Remove ARV cover (4xscrews) carefully as to not destroy diaphram/gasket.
- Pack enough "xyz" material between top of valve and inside of affixed housing (I epoxied a stack of washers, the idea is to not let the valve open at all.)
- Attach cover
- Enjoy whistle-free motoring. YAYYY!
This can also be accomplished by simply epoxying/JB-welding the port itself shut. There are threads detailing how. I wasn't planning on having the turbo off the engine so I didn't go this route myself.
MBZ123