Passat engine pulsing

[stefan]

Hey guys,
My 2005 Passat TDI starting having a little issue. Often, if in gear, but stopped, the engine rpm starts to pulse a bit. Maybe a little faster than once a second. Its not huge, but you can see the tach twitch, and definitley feel it.. If I put it in neutral, it stops, if I move, I no longer notice it. It happens in both drive and reverse.

Things I have done recently include an injector purge, popped off EGR to have a look at the intake, looks fairly clean. Disconnected the MAF to see if it effected the idle, but no. Fuel filter is new. Scanned, no codes.

I had a funny pulsing issue when I first got my Malone tune, years ago. We logged some data, and found he has an EGR setting wrong, but it also caused a pulsing, so I was wondering if the EGR could be acting up. I was also thinking about what the effects of a failing tandem pump or lift pump would be... Short of that, wondering if it could be something bigger like a torque converter or something in the auto transmission.

Anyways, just curios if anyone had some ideas as to what else I could check.

Much appreciated, thanks all!

[stefan]

Re: Passat engine pulsing

I tried to get a video tonight but it's not acting up enough to really see at the moment. Just for reference though, I found this on YouTube and this is what it looks/sounds like.

https://m.youtube.com/watch?feature=...&v=B0FigoWoNp4

[dJ]

Re: Passat engine pulsing

Sounds like fueling to me as it only happens when you first start it and evens out after a bit?

[stefan]

Re: Passat engine pulsing

That video isn't my car. On my car it happens even when hot. Can pull up to a red light and it will start pulsing. When it's doing it, it is pretty consistent. I can sit for the length of a red light and it's pulsing the whole time. One post I read mentioned the lift pump. Wondering if that could make sense as the tandem pump isn't working as hard at low rpm, maybe lift pump is more critical at low rpm? Bit of a long shot.... Hah.

[witchcraftz]

Re: Passat engine pulsing

Might be a vacuum leak, did you test O2 sensor or CCV?

[stefan]

Re: Passat engine pulsing

I am planning to check vacuum lines with a mityvac this weekend. CCV is moving air I think. Not sure how to test the O2 sensor, but I will look in to it.

[stefan]

Re: Passat engine pulsing

There doesn't seem to be any vacuum leaks, and vacuum pump is pulling a lot of vacuum. I also popped out anti shudder valve and egr and ran input tests on them to make sure they were moving ok, and they seem to be.

[stefan]

Re: Passat engine pulsing

Oh, I wasn't sure how to test O2 sensor, but I had another one so I swapped it in but it didn't make a difference.

[kujiwara]

Re: Passat engine pulsing

Check the engine and transmission mounts

[stefan]

Re: Passat engine pulsing

I had time to check the main 2 mounts and they are good I believe. Engine doesn't move much with this pulsing either.

[stefan]

Re: Passat engine pulsing

Pulled return line off of tandem pump today and let it run in to a jar. Getting the appropriate 1.3L per minute. So not that...

[dJ]

Re: Passat engine pulsing

When you're stopped have you tried pulling it out of gear and leaving it in neutral and seeing if it continues? Maybe that will give you some insight as to whether its engine or transmission related?

[stefan]

Re: Passat engine pulsing

It levels out right away when in neutral.
Its not super consistent, or at least the severity isn't. Sometimes it is hardly noticeable. There were a few days there where it as consistently doing it quite badly. Yesterday I didn't notice it though, this morning, it is there ,but pretty faint. So a little strange... I don't really want to book it in if I can't make it happen all the time.
No other hiccups with transmission though, if that were the culprit. Shifts beautifully still.

[witchcraftz]

Re: Passat engine pulsing

You could run a can of Diesel Purge straight through the injection pump.

Sounds like you may need to take it to a mechanic to diagnose though.

[stefan]

Re: Passat engine pulsing

You could run a can of Diesel Purge straight through the injection pump.

Sounds like you may need to take it to a mechanic to diagnose though.

Yes, I have done this already. I have a little 'kit' with a jar, tubing and a little inline filter. I usually do it every year or so.