Idle is backwards

[Aloha911sc]

Just got a new to me 77’ 911s. Starts great and idles around 900-1000. As soon as it warms up the idle speed is 2100. It’s a Ca car with a/c and the smog pump. No thermal reactors, SSI’s and 11 blade fan. Ideas??
Tks

[T77911S]

the mixture is not correct when cold
mixture not correct due to air leak
AAR could be stuck and idle is set wrong


you need to start with checking the control pressures

remove the smog pump and plug the holes in the heads.

[offroader1006]

Yup, check your pressures.

[Aloha911sc]

Wilco, thanks. btw, what’s the AAR?
I plan to remove the air pump and plug the holes. In the meantime is it possible to just remove the belt for the smog pump?

[john walker's workshop]

Pinch the hose closed on the engine side of the air regulator and see if the idle drops.

[Targalid]

you can remove the belt that drives the air pump but that will not change your engine running profile. The air pump provides extra air at the exhaust ports to fully burn any remaining hydrocarbons as the exhaust passes through the thermal reactors. As said above, you likely have excess air entering at the intake side that is giving you a high idle. The auxiliary air valve (AAV) is one place to look as this valve is supposed to close automatically as the engine warms. If it is stuck open, you will have the high idle that you see. The advantage in removing the smog pump and associated air lines is the extra room and easier access to the bottom of the engine. The thermal reactors can be easily replaced with the Bursch exhaust manifold sold by Pelican. That change will help to drop your engine temperatures considerably.

[Aloha911sc]

Thanks Targalid, my TR’s have been replaced with Dansk SSI’s by the PO. Where is the AAV located?

[andy s]

sub

[Targalid]

It is the big round thing on the passenger side of the engine. With the hose removed, you can look into it with a mirror, cold and hot, to see if it is closing as the engine warms. It sounds like it is not. As John Walker says, you can test by closing the "valve" (pinching off the hose) to see if that drops your idle. Read more here:
CIS Troubleshooting for Dummies

[boyt911sc]

Originally Posted by Targalid

you can remove the belt that drives the air pump but that will not change your engine running profile. The air pump provides extra air at the exhaust ports to fully burn any remaining hydrocarbons as the exhaust passes through the thermal reactors. As said above, you likely have excess air entering at the intake side that is giving you a high idle. The auxiliary air valve (AAV) is one place to look as this valve is supposed to close automatically as the engine warms. If it is stuck open, you will have the high idle that you see. The advantage in removing the smog pump and associated air lines is the extra room and easier access to the bottom of the engine. The thermal reactors can be easily replaced with the Bursch exhaust manifold sold by Pelican. That change will help to drop your engine temperatures considerably.

Targalid,

AAV (auxiliary air valve) is different from AAR (auxiliary air regulator). These two (2) CIS components are commonly mistaken to one another because of the language translation from the original German shop manuals to the later English version. If you are referring to the saucer like device it is referred as AAV in this forum. Likewise, the AAR is the device mounted on intake runner #5 with an electrical plug.

Your description above identifies it as AAR not AAV. They look and function completely different and commonly mistaken or referred. Your advice is sound and good.

Tony

[Targalid]

Thanks Tony!

[Aloha911sc]

Well, the AAR is fully closed when warm. Couldn’t find any air leaks. I adjusted the idle screw down. Once cold I’ll try a restart and see how it works.