Subsequent mechanical failures

[designation_mi5]

Hi all, hoping I can get some insights. FSI, 2008 GTI. Here's the history:

I recently had my thermostat replaced to solve a P2181 CEL and a temp gauge that never reached center. Everything looked good.

CEL came back on, mechanic said there were two codes. They replaced the coolant temp sensor and the hpfp sensor. CEL was gone, drove fine.

CEL came back on when I was on the highway. 20 minutes later the engine felt like it was stuttering, it's driving a little rough and makes a deeper sound. At a stop light, I shifted into park and the revs died. Car started back up in one try and I was able to drive back home. I can't replicate the revs dying.

I also noticed that when the car is put in accessory mode, there's this strange motor/whistling sound (like one of those motorized robot toys) coming from the rear passenger side. It makes the noise for a few seconds then stops.

The car has roughly 60k miles on it. Cam follow replaced at 40k, spark plugs changed 20k miles ago.

This is all very stressful, especially with problems seemingly popping up just when something else is fixed.

If anyone has any insights, I'd really appreciate it. Thank you very much in advance.

 

[donjuan1jr]

P2181 most of the time is a faulty thermostat, those coolant temp sensors are so basic they never go bad.

If the car died at idle you could a rather large vac leak somewhere.

That noise u hear when putting the key into acc is the pump priming fuel, you lpfp is located olunker the right rear part of the bench seat.

 

[Timpanogos Slim]

ECT sensors do so fail. The thermostat failures are far more common though.

It's telling that the thrust sensor on the HPFP was replaced, because the only thing with a motor in it in the rear passenger side is the LPFP. The thrust sensor is responsible for verifying that the LPFP is delivering the correct pressure to the HPFP, and sometimes that thrust sensor does fail (there was a recall) so that was a sensible thing for the mechanic to try as a first pass. I did the same thing.

LPFP failures are common too, and they don't typically manifest in the winter because gasoline gets thinner the hotter it is. It was exactly this time of year when mine started causing hard fuel cuts two years ago.

My guess is that your LPFP is dying. You can verify this by hooking up VCDS (vag-com) and measuring the fuel pressure as described in the ross-tech wiki:

http://wiki.ross-tech.com/wiki/index.php/2.0l_TFSI_%28AXX/BGB/BPJ/BPY/BWA%29#Checking_Fuel_Pressure

Also, buy a genuine VW pump. I personally tried to save a few bucks by getting a VDO pump from a parts supplier. The pump i received had the factory markings shaved off but the box bore an SKU that pegged it as a pump for a Polo with a 1.4 TSI that is not rated to deliver the pressure or volume required for our engines, so i sent it back and got a genuine unit from 1stvwparts.com (which is Auburn VW in the Seattle area).

The part number is 1K0919051DB

In the mean time, removing the back seat cushion is a reasonable band-aid. I'm not kidding at all. Some people go as far as to lay a bag of ice on top of the pump access hatch.