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vwtech0405, VW Technician
Category: VW
Satisfied Customers: 10670
Experience:  VW Master Technician VW Certified
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Pulling my hair out on this. 2006 Jetta 2.5. right now code

Customer Question

Pulling my hair out on this. 2006 Jetta 2.5. right now code is P0507 revs higher than expected. I have had P0101 mass air performance, P0171 lean. I replaced the torn pcv diaphragm with a Dorman kit and that didn't do much, had lots of crankcase vacuum until I shortened the spring on the diaphragm, then vacuum was normal. I am giving up on that today though and ordered a new VW valve cover. On a test drive yesterday all seemed well and check eng light was off until all of a sudden it would keep the revs way high, like 3k, when you lifted the throttle. Eng light came back on for P0507 revs higher than expected. Throttle has been cleaned. High miles, 175k, runs very well. Used car lot here, can't pass e test with light on. No apparent vacuum leaks. Hose to pcv is good. Help please, Jack
Submitted: 1 year ago.
Category: VW
Expert:  Matt replied 1 year ago.


This could be an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane around each joint in turn. If the engine rev's up you've found your leak.

Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.

Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

It’s also worth getting the fuel pressure checked as if this is low due to a blocked filter or faulty regulator or even a poorly pump will all result in insufficient fuel being delivered to the engine

Might also be worth cleaning out the throttle body as these get clogged up with carbon and some brake cleaner washed through helps free things off.

Might also be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.

if the engine condition is the same then chances are the meter or the connection to it is faulty

Air leaks are very temperature dependent as gaps can open or close up as things expand with heat, so the weather and engine temperature can effect them.

This leads them to be quite intermittent in the case of mild leaks

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile

Customer: replied 1 year ago.
there are no air leaks. Have used propane and the smoke machine. Are you a VW line tech? I know this motor has some peculiarities and I was hoping to find someone very familiar with this setup.
Expert:  Matt replied 1 year ago.


I'm not a dedicated VW tech so I'll opt out if you would prefer someone else

however these cars can suffer from the brake booster leaking over time and the engine then Leaks through this area

if you clamp off the vacuum pipe to the booster and the situation improves then its possible that this is the problem

Customer: replied 1 year ago.
I need a VW tech familiar with this car. They're a little different, like brake booster hooks directly to vacuum pump with no connection to intake. Please opt out, Thanks Jack
Expert:  Matt replied 1 year ago.

Fair enough

good luck

Customer: replied 1 year ago.
thanks Matt. I hope somebody chimes in
Expert:  vwtech0405 replied 1 year ago.

I can help you , has you received the valve cover yet ??