Intermittent delayed boost

So I've noticed since I've had my tune done, sometimes my car is fast to accelerate from a stop and from moving speeds, and other times it feels like it is lacking in boost. Seems to be far and few between, but when it does its like it happens when the car is fully warm.

Last time I checked the vac pump at idle it was at 23inhg, almost wonder if it's performing poorly when warm. I can do an actual vs specified boost if needed.

Any ideas? I have a new Bosch maf and the turbo actuator isn't stuck, and properly adjusted.

To better clarify, because I was toying around with it on my way into work, if I just mash on the throttle, feels like boost never catches up. If I back out of it to half throttle, then slowly press down to full throttle, then it gets up and goes. If I am gradual into it, I have full power through the whole RPM range.

Seems like only when I mash on it, it doesn't work. But only sometimes.

interweb guesses-
Bad vacuum tubes, leaky vac pump nipple, bad N75
reference

Make sure you have no intake or exhaust leak,
check also if EGR is working correctly,
Check vacuum hoses
Change hose if possible
Swap N75
Maybe beginning of sticky vanes

Take a look at the hard plastic vacuum line to the brake booster,mine started with weird boost and then one day my brakes weren't there and I knew exactly what was wrong, cut the ad off and heat gun the end and slid it back over, it's like it was before

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Guess I should have specified... Brand new N75, brand new EGR valve, brand new vac lines, ran silicone around the vac pump at the inlet, checked the check valve.

I hadn't checked the hard plastic line lately, I can do that in a little bit. My brakes seem to be working OK for the most part.

I don't think it's sticky vanes, because it still has its full range of movement with my mighty vac, but there still could be junk in there.

I also made a homemade boost pressure tester, from the outlet of the turbo while leaving the intake bolted on, I could apply shop air up to 30psi and no leaks at all. I then tested pressure from the MAF to the turbo intake at 3 psi, and no pressure drop.

I also have no soot tracking from any possible exhaust leaks.

I've read about the go pedal which houses the throttle position sensor can start to flake out. I've also read that some have opened that housing, and cleaned it out with de-ox-it with good results.

Maybe when warm (floor blowers on?), something in the housing expands just enough to cause...something? Cheap to rule-out anyway.

STDOUBT said:

I've read about the go pedal which houses the throttle position sensor can start to flake out. I've also read that some have opened that housing, and cleaned it out with de-ox-it with good results.

Maybe when warm (floor blowers on?), something in the housing expands just enough to cause...something? Cheap to rule-out anyway.

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You might be onto something. I've noticed in VCDS that the throttle position sensor only reads max of like 86% or something like that. When I got the car the bulkhead connector was leaking lots of water onto the drivers floorboard. Might be a failing sensor. I have a spare I'll try dropping it in this weekend.

Nero Morg said:

You might be onto something. I've noticed in VCDS that the throttle position sensor only reads max of like 86% or something like that. When I got the car the bulkhead connector was leaking lots of water onto the drivers floorboard. Might be a failing sensor. I have a spare I'll try dropping it in this weekend.

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Is there an output test you can do to watch the discrete steps of the pedal sensor through vcds? Ease into it and matt and see if you see any difference or abnormal activity. It isn't too hard to change the go pedal but I hate working under the dash.

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There's not really an output test per say, more of watching one of the measuring blocks for the pedal. Does anyone know if our pedals ever truly read 100% throttle when it's to the floor? Mind you it is an auto converted to stick, so it has the kick down button, but still only reads to the 80s

Same issue on my car, would be curious to find out what fixes it. I have a new gas pedal, EGR system deleted, intake manifold and turbo 3 yrs 80k kilometers old, my actuator moves freely as well, all new vacuum lines, N75 2 years 50k old. Can't figure it out for the life of me. How much variation was there between specified and actual boost in VCDS? there was about a 40mBar difference in mine, compared to a known good car there was only a 20mBar difference, currently dont have access to a vagcom so haven't bothered trying to adjust the actuator yet

I hadn't measured mine yet, going to try and do it this Sunday, kind of juggling overhauling an engine in a 03 nb along with doing a steering rack in a grand prix. The joys of being a mechanic.

Today on my way into work my car performed great. So irritating.

So brief follow up, still intermittently lower on power than it should intermittently. Finally found a way to route a vacuum line through the firewall and now have a vac gauge next to the cluster, I'll monitor it while driving.

I tapped it in at the check valve where the main vac feed comes off the hard plastic line, for diagnosing this is that the best place? Also, how fast should these little pumps build vacuum, and how fast should it bleed off when you shut down the engine?

OK, was able to maintain at least 25inHg of vacuum the whole way to work.... I almost think it's the actuator is getting sticky finally, because it did act up a few times on my way in.

Nero Morg said:

OK, was able to maintain at least 25inHg of vacuum the whole way to work.... I almost think it's the actuator is getting sticky finally, because it did act up a few times on my way in.

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I know mine is very sticky now.
Since I retired I don't do my daily Italian tune up.
It's mostly local short drives, 5 to 10 miles.
When I can get on a lift I want to take the actuator off (2 or 3 years old +/-) and check the arm.

If you take your actuator off check for rust inside it. VW has a bulletin about it.
Tie a piece of thread or dental floss to the clip on the arm so if it flies when you reinstall it it's easier to find.
There a couple in mine somewhere.

Last, with the vacuum gauge on the line try wiggling the fitting going into the vacuum pump while the engine is running.
It will probably be loose but give you an idea how much vacuum you might be loosing going down the road as the motor shakes and torques back & forth.
Mine dropped quite low.

Best thing I found was an 2 part epoxy paste.
It's loose again so I want to try making a small brace to attach to the fitting and the pump somehow.

I've already ran sealant over the vacuum nipple, and so far I've had consistent vacuum since I installed the gauge.

I also have replaced the actuator once before. Next time I change it though I'll have to remember the string trick. I've lost one of those E clips once already.

I do drive my car a bit on the hard side, plenty enough to keep it Italian tuned. You can feel when the actuator is working, and when it's stuck easily all within the same drive. No key cycling required. I may go pull the actuator off tomorrow and check it out...