Bucking, Surging, hard starting issue.

Any ideas appreciated.

I have a 2005 passat tdi. 203,000 miles. Recently it has been hard to start in the the morning and after it has sat for some time. Outdoor Temps have ranged from 0- 68F.

Once I get it running it randomly "bucks". it's kind of like a misfire some are worse than others, it happens at all speeds and even when it's in park. Things I've recently checked or changed related or unrelated are below:

Torque converter at 197,000
timing belt water pump etc.
fuel filter x2
gaskets for tandem pump, valve cover, oil cooler.

things I've checked over:

boost hoses
wiring connections to injector harness
cam (no signs of wear)
lift pump working
replaced maf to no avail
injector cleaner.

also I've checked it on a VagCom. there are no codes and all of the numbers seem to be correct.

I've also scavenged the forums extensively and have not seenthis exact issue discussed AFAIK.

Thanks in advance for any help!!

Well 3-4 months ago I had the same thing and did everything you have done. I finally replaced the tandem pump with a used one and it cured my problems.

Recently, it has been taking a while to start, so I decided to rebuild it with a kit I bought. So far so good with no issues. Will see how it goes.

where can I find a rebuild kit?

Here http://www.ebay.com/itm/Tandem-vacu...-2-0TDI-SDI-/181882478177?hash=item2a590a5e61

If you end up removing the tandem pump, consider replacing the coolant flange, gasket, and coolant sensor as a preemptive measure. That is unless you like taking the tandem pump on and off again

Is it important to chance the hardware (bolts) when changing or rebuilding the pump?

The kit comes with all new bolts for the pump itself. If you are talking about the 2 5mm and 2 6mm allen bolts that hold it to the head, no. Reuse them.

As (un) luck would have it, my coolant flange is leaking so I'll change that too.

I ordered a new tandem pump and coolant flange. Haven't gotten to put them on yet. Now I'm getting P0726 code and it won't allow the car to start. I erase it and it starts up and runs fine. Will my new tandem pump cure this all once it helps with the hard starts?

Edit: I believe the code was due to extended cranking. I changed the sensor anyway so far the code has not returned.

Today I changed the Tandem pump with a new pierburg unit, also the coolant flage.

NOW IT'S BUCKING WORSE! Harder and more often. I drove it about 30 miles.

Can anyone give me any insight into this issue?
I checked it out with vag com again, still no codes. This is baffling me. What am I missing?

Changed the crankshaft sensor as well. Forgot to mention that. That seems to be fixed, although I think it was due to extended cranking more so than a bad sensor.

On a drive today, I noticed that it starts and idles ok now. The bucking really doesn't start until the car gets warmed up to operating temp. I ran it about 5 miles and i was starting to think everything was ok....then as it approached about the 190F mark, it started bucking really bad, and stalled out at 2 lights on the way back.

Things I tried today...unplugging the egr. No change then the MAF. No change. So it isn't a metering issue. I dont think. I think its fuel.

Is there a screen on the fuel pick up in the tank ?

I believe there is though I have not pulled the pump, only confirmed that it runs.

Solved!

Faulty crankshaft position sensor.....then a faulty replacement. I bought one from the dealer. Smooth as silk. Thanks for all your help.