What's the difference between AAR and AAV

[Lmarche]

I'm trying to understand how does the K-Jetronic with lambda system works.
I understand that AAR, is an automatic choke, that stops bypassed extra air when warm, reducing the rpms.
What's the function of the AAV? how does it works? When does It works?

My 1982 911sc K-jetronic w/lambda it's experiencing a cold start problem. When cold engine ( outside temp 8C or 46F ), it takes around 8 secs of starter to light up, followed by a 3 sec. period of relative stable 900 rmps, then 20 sec. of jumping rpms ( between 1400-800 ), and then the rpms stabilize sometimes at 1200 and Ithers at 1050, til they slow to 950 at warm-up end.

The only other sign I noticed is a slight rpm change ( from 30-80 rpm ) right after the engine temperature departs the lower white block of the indicator, til it rises above the first thin line.

Thanks for any help.

[timmy2]

AAV supplies an extra gulp of air when first starting, it gets closed with vacuum.
Many have removed and plugged the small vacuum line and the nipple on the Decel valve that looks the same as the AAV but with a nipple due to the issues you have described.

[boyt911sc]

Originally Posted by timmy2

AAR supplies an extra gulp of air when first starting. On your car I believe it gets closed with vacuum. many have removed and plugged
the small vacuum line and the nipple on the AAR can.

Dennis,

AAV (auxiliary air valve) supplies the extra gulp of air when first starting. AAR (auxiliary air regulator) by-passes the metered air during cold start allowing higher engine speed during a cold start. The saucer-like device with the small nipple for vacuum line is the deceleration valve.

Examples of Bosch CIS components:

0-280-140-218.........is referred as AAR in this forum but sometimes called as AAV by others including some reference manuals.

0-280-160-400.........is referred as AAV in this forum oftenly interchanged with AAR.

0-280-160-324......... is the deceleration valve (with nipple for vacuum line)

AAR on the left and AAV on the right below:


Tony

[schumicat]

I just did troubleshooting the AAR and it is very easy using instructions I found in a search (unless you have a/c in which case compressor limits access). see this thread

Warm up issue and access to AAR

[timmy2]

Tony, I knew that, my phone made the typo. Fixed my post.
To the OP, look up the Jim's Basement guide for the Bosch CIS system. Or someone could post a link.

[Lmarche]

Thanks for your comments,
last question ofthe day, How does the valve operates?, if it closes with vacum it means it closes right after startup or it retards closeup?, again if its vacum it also opens during warm engine start? can I try to clean it?

Of course I have to do a fuel pressure test, but is it fair to suspect that my AAV has failed?.

1. The rmps jumping during cold start make me belive the mixture is to rich because there's not enough air.
2. I can smell gas coming out of the exaust when cold starting the engine, but it takes around 8 sec to light up. It seems start valve is opening but again not enough air.
3. I forgot to coment that after warm engine start up, the idle rmps stay around - 800 for around 3 minutes. I suspect AAR is closed because is warm, but maybe AAV is not supplying enough air for proper rmps.

Is always good to know there's backup, Thanks for your help.