Buzzing N75 After Startup

What would cause the N75 to buzz after ignition? When the car is started the N75 will continuously buzz until the car is turned off and restarted. I would say the N75 does this 2 out of 5 startups.The N75 was replaced a few years back due to loud buzzing after the car was shut off as well as limp mode issues. I have had this problem intermittently over the last year or so. After replacing the starter and alternator it seems to occur more often. Not sure if the warmer weather is having effects. There seems to be lots of threads of buzzing N75s after shutdown, not so many buzzing N75s after startup when the engine is running.

Where did you get the replacement N75? Bosch or aftermarket?

I got a Pierburg N75 solenoid as a replacement. In fact the car had a Pierburg on there when I replaced it

Only thing I can think of is some folks reporting crud in the vacuum system, from rusted actuators and such. I believe (please check) you can carefully clean these out with maybe some light oil (WD40) and/or air.

try googling it, I remember reading a post with that problem in it recently, I don't remember where though

Just out of curiosity, has anyone thought of putting a small filter in the line coming up from the VNT actuator? I wouldn't want to put much of one, but if you put it up at the N75 end, you could see if any debris was coming up the tube, and also keep it from being ingested into the overly expensive valve.


I would think that a small fuel filter intended for use on a lawn mower or something similar would give decent filtration while also being small enough to not act as a significant vacuum reservoir.
I know that there are also filters intended as last resort debris screens, rather than truly being filters, but have no idea where to find those little things. The ones that I've seen looked almost like a check valve, but with a fixed membrane in the disc, instead of a valve.

Resistance in that line would probably change the vacuum at the actuator, but try it and see

'Buzzing' is kind of the way the N75 is used by being fed a stream of on and off pulses.
I would suspect the ECM is activating it because of bad data or a bad connection.
Worst case being a defective ECM, best case being a loose wire.

The N75 is very easy to blow clean with air if you suspect rust or debris, too.

How do I go about cleaning? Just spray through the ports with compressed air?

Low pressure maybe 15 psi and cycle the valve on and off either with 12V or vcds.

Fixed the buzzing. Turns it out was my N18 buzzing. Since my EGR valve, and cooler have been disconnected for years I rerouted my vacuum lines. Removing the N18 from the system. The annoying buzzing is officially gone! Is it possible to hook up the ASV without an EGR valve? I’d love to get the car to shut down smoothly once again.

Look up wingnut's 'stealth racepipe'.

This may help-
http://forums.tdiclub.com/showthread.php?t=290286

jbourke367 said:

How do I go about cleaning? Just spray through the ports with compressed air?

Click to expand...

I sprayed WD40 in one of my N75 valves then lightly blew air through the 3 ports.
It did make a difference in the car running but did not last that long.

When I replaced it the car ran better.

My actuator was replaced a few years back. I did not have rust in the one I removed.