Slightly fast idle - suspect AAV, Am I right? Options

[gturner008]

Owned 76 2.0 for two weeks now.

Lots of little jobs completed. But I have an idle that’s 1100 rpm. The idle screw is virtually fully in.

I suspect the AAV is stuck slightly open when engine hot. If I pull the tube from the air intake and put my thumb over it, the revs drop to about 600 rpm.

Everything else is good. All hoses correct and no leaks.

Am I right in thinking the AAV should close up completely?

If it’s a stuck AAV, any recommendations for getting it freed up?

Cheers. Gary

[BeatNavy]

Fast idle is normally caused by vacuum leak and/or timing too far advanced. The AAR/AAV is essentially a managed vacuum leak. Yes, the AAR should basically close off all the way. But if you plug that hose and your idle drops to 600 -- that's too low and something else is going on (or I guess you need to open air bypass on throttle to compensate if you have it fully closed off).

Take the AAR out. You can test it by grounding the base and carefully attaching the lead to 12v. You can look inside and gradually see the valve close off over the course of 5 to 10 minutes. If it's sticking, spray PB Blaster in there and let it soak for a while before shaking it out. Try that a couple of times. If that doesn't work, you can try to carefully pry open the can, take it apart, and give it a more thorough cleaning from the inside. Try not to break the wire lead as those are pretty fragile after all these years.

Good luck, Gary.

[gturner008]

Many thanks. The drop to 600 rpm I think could easily be adjusted using the idle screw on the throttle body. At the moment, its almost all the way in. The timing is correct - along with no vacuum leaks the best I can tell.

I'll remove the AAV, and try and get it to close fully - but the soaking and cleaning method. Hopefully I don't need to pry open.

Appreciate the quick response. As I newbie to 914, I'm just finding my way.

[ClayPerrine]

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Glad you are here.


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We want to see your 914!

[gturner008]

Work in progress

[windforfun]

What's the AAR or AAV?

[pete000]

Sure doesn't take much of a leak to reek havoc on a L-Jet idle...

[Dave_Darling]

What's the AAR or AAV?

Auxiliary Air Regulator (or Valve). Gives you a higher idle when the engine is cold. Serves as a leak from upstream of the throttle valve to downstream of it; is open when cold and closes when it heats up as the engine runs or as the small heating element in it warms up.

On D-jet cars (1.7, 2.0) it lives to the front-left of the Intake Air Distributor (the plenum part of the intake manifold). I think the location is similar on the L-jet 1.8s, but I don't remember.

--DD

[gturner008]

Update.

Removed AAV or ARR, cleaned. Put 12v through it.

Got it to close right up. Reinstalled. Ran car to hot. Valve closed off completely as pulled pipe and thumb over. No drop in revs.

Car now idles at 1000 rpm, with idle screw fully in.

I’m thinking I now need to check timing. Can’t think of anything else.

Again, great advice. Now sorted the AAV.

[euro911]

IIRC, there's two idle adjustment locations on the 'late' ,models ... one on the throttle body, the other is on the top of the ECU (IMG:style_emoticons/default/confused24.gif)

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[BeatNavy]

Great job! You may have a small vac leak somewhere else if it's not timing related, but overall it sounds like it's solid now.

[gturner008]

Thanks Mark and Rob,

I'll give the ECU a tweak, and see if I can find that 500 rpm. I may have a very small vacuum leak - but I've triple checked all lines and they are good.

Timing needs doing I think - as it was done - but many years ago.

You are right, its pretty much sorted now and running extremely well. Smooth and decent power.

I also need to get it tracked, as I attempted to do a DIY with string and messed it up!