B230e aav issue
 

Hello all,
I have an issue with my aav. When the car is hot it struggles to start so I have to spray a load of carb cleaner into the aav which gets it starting again. After a while though it happens again. I have taken it off the car and cleaned it thoroughly but it doesn't make much difference. Is there anything else I can try or should I look for a replacement? Thanks
Joe

From what you say I would think your fuel system is not holding pressure when you turn the engine off , It should hold fully ( about 3 bar ) for at least 20 minutes .

I'd agree with Clan here, the AAV will still be hot so should by rights still be closed and therefore addiing carb cleaner is really only going to see the carb cleaner evaporate and be pulled into the throttle body as "fuel".

When was the fuel filter last changed?

Also have you tried starting as for a flooded engine? Ignition completely off, push the accelerator to the floor and hold it there. Turn the key all the way to position 3 and hold for 7-10 seconds or until it starts, whichever is sooner. If it doesn't start on the first attempt before 7-10 seconds, release the key and allow it to come back to position 2, wait 5-10 seconds and turn to position 3 again.
When the engine fires, release the key and the accelerator to the point where it's running at a fast idle (~1500rpm) then gradually release it until it's idling smoothly.

If starting as for flooded gives a good result, you may have one or more leaky injectors, Comma injector cleaner should help with this.

Thankyou for that. Fuel filter was changed about six months ago. I'll give your suggestions a go and let you know the result. Thanks very much.
Joe

I had the injector o rings replaced about four months ago too which sorted out a lumpy idle. Maybe that had something to do with it.

It's doubtful they're linked, however if your old injector "O" rings were leaking then it would allow the fuel to evaporate out of the inlet manifold if the injectors were leaking. By disconnecting the AAV you're releasing the fuel vapour to atmosphere, filling with carb cleaner (which is fairly volatile) would help the engine fire quickly.

The AAV is simply a cold start device, a small valve operated by a bimetallic strip. When cold, one side of the bimetallic strip contracts more than the other causing it to bend which in turn opens the valve. The two ends of the valve are connected via hoses to either side of the throttle butterfly so when cold, it provides a path for extra air to be admitted to the engine. With the ignition on, the AAV has power going to the small heater built into it which heats the bimetallic strip which closes the valve as it heats up. Heat from the engine helps keep the valve closed after a journey until the engine cools down at which point the valve opens again.
It's not a "dynamic" thing, it doesn't move according to need at any given time like the AICV (Air Idle Control Valve as fitted to later EFi models) which is modulated by the ECU to maintain the idle speed under many different scenarios. The AAV is simply open or closed with a short time in between as it heats or cools.

Hopefully that will help make it clearer as to why two people have separately arrived at a similar conclusion as to the probable cause. :thumbs_up:

Thankyou. That makes more sense. I tried firing the car up as you suggested as if the engine was flooded, ie accelerator down. Fired up straight away.

You might find the normal hot start procedure of putting your foot halfway down works just as well, glad it worked for you anyway! :thumbs_up:

Brilliant. Thankyou once again.

Morning all. So it won't start from cold now without the help of carb cleaner which I really don't want to keep using. I'm going to buy some injector cleaner today but wondered if there is anything else I should be looking for? Thanks in advance.
Joe