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I have a audi 3.2 vr6 a3 with a strange problem. between 1500 - 2000 rpm it jerks and hunts but only when im very light on the gas. iv changed the plugs but no help there. i am about to buy a cam sensor because thats my next guess. there is no check engine light. been to 2 mechanics even to audi and they have no idea.. when this happens the rpm needle is moving very fast between 60 to 100 rpm.
I should also mention that the car has no other problems when I drive it is fine. just when im light on the throttle it jerks and is very bad at 80kmh when in 6th gear it is almost exactly at 2000rpm when at 80kmh. although it does it in other gears between 1500 - 2000 rpm aswell just not as much.
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.
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 idle speed control motor / valve 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 throttle body as they can get quite choked up inside
On no account touch the sensor wires with anything physical as they are extremely fragile
so it doesnt sound like a sensor problem? i was worried it also was to do with the trans and or the cam itself.. i will listen tomorow for a hissing sound.
I think I can hear what you would say a hissing noise from the back of the engine when i open the bonnet when it is warm. Is that where the Air flow meter is located on the 3.2 vr6 motor?