My Euro S 16v MY86 has developed an unusual fault. When accelerating, and then releasing the throttle, there are a couple of loud clicks from the passenger footwell area, or maybe deep in the centre console. low down. Firstly when the foot goes down, then then again on releasing the throttle.

The number of clicks depends on how much right foot is applied.

The car may do this for a few miles, and then the noise goes away again.

Engine vacuum looks pretty normal, maybe a little low.

Any ideas ? HVAC diaphrams ? Moving the HVAC controls around has no effect.

 

Bumpy, bump !

 

I recall some year/models have an O2 mileage counter, I think located under the side cover near the sill that can act up and click, but I can't make the connection to acceleration and the location isn't quite right. As it's coming from the passenger footwell, I would consider a relay malfunction, but, again, I can't quite make the connection to acceleration, other than the kickdown relay perhaps. But I would not expect that to click until the kickdown is tripped.

Can you uncover the CE panel and have a passenger try to localize the source while you drive? If it's in the console, perhaps removing the console side covers and having someone probe for the source with a length of heater hose for listening would help locate the source. You may be onto something suspecting a vacuum leak in one of the actuators or perhaps the climate control solenoid pack behind the radio, as vacuum varies with throttle position. That solenoid pack is a bitch to remove due to the way it's screwed in by 3 screws, one in the center of the console, but once unscrewed it can be pulled to the side and observed. Leaks there in the rubber manifold are common. I leave out the center screw when I reinstall it. Why this noise would disappear after a few miles, if vacuum, isn't clear. Exhaust leaks will do that as the exhaust heats up, but this isn't an exhaust leak noise.

 

Hi Bill, thanks for the response. My car doesn't have a mileage counter that I know of. The throttle openings that is happens at at quite mild, certainly nowhere near KD.

Yes, I do need to get more methodical about tracking the noise down to a more definite location. Preferably using a small person who can get down close :-)

I thought perhaps that this is a problem that had been previously investigated here on RL.

 

Could be vacuum "playing" with a weak vacuum valve. Try disconnecting the vacuum source for all the interior vacuum valves, in the engine compartment. Should be a black hose, going into the firewall just behind the engine. Disconnect and plug the side going to the engine. The heater will/should come on.

 

Thanks Greg !

 

As Greg said, can be a vacuum glitch. Check the little black/blue check valve at the brake booster to make sure that it only allows flow one way.

 

OK, will do, I seem to remember that valve shows some signs of heat damage to the moulding...

 

What the part number for black/blue check valve at the brake booster ? I've searched PET with no luck for a positive identification ...

 

John,
This is the PN from 928intl - 843 820 675, however I believe this is a VW PN.
http://www.mailordercentral.com/928i...asp?number=843 820 675

 

John,
I'm not as adept at using PET as I should be but if you put that number in PET and do a search it comes up with "Check Valve"???

 

This is one of those things I thought would take 30 seconds and I'd be done, but no...
Anyway, it looks like the unit is part of an assembly in the PET, search for 928 574 710 08, or go it illustration 813-05, I think that part is actually what you're looking for.

 

http://www.mailordercentral.com/928i...43%20820%20675

EDIT: Oh, I see Thom is already all over this.

 

Many thanks, Thom and Bill. I'll start by changing that valve in the hope of a simple fix, before digging deeper !

 

Well, the blue/black vac check valve measures fine. It feeds into a 3 way splitter (two ouputs) one output (blue hose) goes off to the inner wing, so feeds the cruise reservoir. I can pump up a vacuum on this ok, with a lot of pumping on the Mityvac, but once up to 15"Hg it holds. The other black hose goes to a point about half way along the firewall, is this the vac feed to the HVAC or to the auto trans ?
It also holds good vacuum.

I had a look under the engine airfilter lower section and there's another 3 way splitter near the valley, this just feeds the two FPReg at the back of the engine. Back to the WSM...