Surging/bursts of power

[4x4_Welder]

My 83 Rabbit TD occasionally gives a bit of a surge of power, like the throttle is hanging a bit.  There is no smoke and if I let off the throttle completely it will idle down.  I changed the fuel filter last week, and did an oil change with Delo 10w30XLE since that is what we have in bulk in the shop.  It was doing this before, but has progressively gotten worse.
The last vehicle I had behave like this was a Ford 7.3IDI, when the lift pump failed the lack of case pressure made the timing go high randomly, but I see these don't use an external lift pump. 

[RabbitJockey]

for one, you need to run the proper oil, drain that *** and run diesel oil.  then i would start by running some diesel purge through the injection pump.  have you adjusted the fueling on the pump at all?

[TylerDurden]

I'd also check that the IP mounting bolt under the injector lines is snug.

[srgtlord]

I thought Delo made a 10w30 that was diesel rated?

[RabbitJockey]

I thought Delo made a 10w30 that was diesel rated?

you're right im wrong.  sorry.

[4x4_Welder]

I know a few things about diesels, but not specifics about VWs yet.  At the shop we run 15w40 (currently out), 10w30XLE in the HEUI engines like 7.3 and 6.0 Powerstrokes (helps with injector stiction issues), and full synthetic 5w40 (not cheap).  I went with the XLE since it's winter and a thinner oil makes for easier starting.  I was going to put the 5w40 in it but not until I fix the turbo.
I did check those bolts, and found the bolts holding the bracket to the block loose.  Actually, one was loose, the other missing.  I tightened the one and the surging is gone.  I also now notice a change in note when I pull the start knob that wasn't there before. 
I do have to wonder, does this being loose really change the timing that much?  I can't imagine it's good for the timing belt, but in my experience it takes 3-5 degrees of timing to make these sorts of events happen.

[Toby]

DELO = Diesel Engine Lubricating Oil

[Rabbit79]

I did check those bolts, and found the bolts holding the bracket to the block loose.  Actually, one was loose, the other missing.  I tightened the one and the surging is gone.  I also now notice a change in note when I pull the start knob that wasn't there before. 
I do have to wonder, does this being loose really change the timing that much?  I can't imagine it's good for the timing belt, but in my experience it takes 3-5 degrees of timing to make these sorts of events happen.

I had the exact same thing happen several years ago. I'm like you in that I wouldn't think it should make that much difference but apparently it does. When I put new bolts in I put blue Loc-tite on them.... no trouble since then.

[ORCoaster]

When you consider that just a pencil line thickness of change has such an effect on the overall starting or running of our engines it is not that much of a reach for changes to happen with loose bolts.  Especially when there is a lever attached that may make the actual distance much greater than just that little bit at the head of the bolt itself.

[vanbcguy]

My 1.6 had a really weird surge when cruising at around 1800 RPM that was bad enough I'd avoid that speed all together. Turned out to be a missing bolt at the high pressure end of the pump. There's definitely some harmonics that can happen if things aren't good and tight.

Also worth mentioning - if you have your dial gauge in place while you do the final tighten of the pump bolts after setting the timing you'll often see it move by up to 0.05mm, enough to make a noticeable difference. That's just from tightening up a bolt!

Sent from my XT1097 using Tapatalk

[fatmobile]

How's the belt tracking after playing with those 2 bolts?
 Put some blue lock-tite on them.

[4x4_Welder]

I haven't rechecked it in the last couple days, we've been getting some snow and work has been insane.  I may have a look at it tomorrow, I need to work on my tractor.

[air-cooled or diesel]

-a--

[air-cooled or diesel]

^the above post was/is primarily to check cam(lockout)----