Rattle off-throttle in 118TSI

**cwcarruthers** · 30-12-2009, 12:58 PM

My 118TSI has a loud rattle (well, it could easily be missed with the windows up, but with them down it is very obvious) when the revs are 2000+ and I come off the throttle. This is most often when in Sport mode, as the revs are kept high enough. As soon as there is any throttle applied, or if the engine is loaded e.g. going down hill, the rattle goes away. It's like a free-wheeling ratchety noise.

Does anyone else have this, or know what the problem is? I assume it is not normal!

**kingwang** · 30-12-2009, 03:04 PM

you've bought ur self a proton

**cwcarruthers** · 30-12-2009, 09:03 PM

Originally Posted by kingwang

you've bought ur self a proton

Thanks, that's really frickin' helpful.

**Corey_R** · 31-12-2009, 08:30 AM

What'd you expect from someone with a nick such as that

I've had an off-throttle rattle in previous non-VW cars. Was just something lose in the engine bay. It could be numerous things really. Best to get your VW service rep to jump in the car with you and drive it around the block and point out the sound to them

Edit: Oh, does it to it whilst you're stationary if you rev the car (slow constant rev to 'similate' driving engine speeds)? If so, get someone to poke their head in the engine bay whilst you're doing that

**mr gee** · 31-12-2009, 11:28 AM

mine makes a fluttery noise when I come off the throttle which I take to be the DV working. Could yours be the same?

**cwcarruthers** · 31-12-2009, 11:45 AM

Originally Posted by mr gee

mine makes a fluttery noise when I come off the throttle which I take to be the DV working. Could yours be the same?

DV?

Mine is definitely a rattle rather than a flutter, though.

**logger** · 31-12-2009, 12:26 PM

I think by "DV" he means dump valve which the twin charger does not if fact have. It does have a air recirculation valve though and perhaps yours is staying closed (loose wire etc). Dump valve does as the name suggest and dumps the pressure to the atmosphere, whereas recirc valve connects turbine and compressor sides of the turbocharger. The boost pressure is suddenly reduced and backflow is prevented.

Anyway this recirc vallve is there to prevent compressor surge which is "When the throttle plate on a turbocharged engine closes, the high pressure air in the intake system is trapped by the throttle and a pressure wave is forced back into the compressor. The compressor wheel slows rapidly and may even stall, and the driver will notice a fluttering air sound."

If your are hearing fluttering on back off I would suspect the recirculation valve is not functioning as it should. You can probably test it by disconnecting the lead. Depending on if lead disconnect fails it open or closed it will either reduce avail boost or preclude recirculation, creating the noise on backoff. Should be just a single sensor connected to the side of your turbo.

On the other hand if it is as yo say a rattle could be something entirely different.