AAV and Decel Valve

[eubanksae]

Hi, I have a 1978 SC and the idle hunts until the engine warms up, then if I park it for a while (hour or so) it is then very hard to start. Right now I have the idle adjusted too high, to compensate for the problems, and to keep it from stalling before it warms up.

I have seen in various post that people plug or disconnect the AAV, and in other posts I see mention of disconnecting the Decel Valve. Why?
Is this something I should consider doing, and if so, what is the proper way to plug them?

Thanks,
Andy E.

[jeff m]

Andy
Your AAV will/should give you more metered air, raising your idle until the car is warm.
It should be open when the car is cold. check this first. When that is done readjust your idle and then reassess the problem using the CIS chart in technical articles.
Jeff

[Sean Hamilton]

Don't confuse the AAV with the AAR.

AAV = Auxiliary Air Valve.
The AAV is a useless appendage (IMHO) that makes cold starting a surging PITA! Plug it!
Remove both top and btm rubber hoses. Wrap the two AAV metal hose connectors "RED" with duct tape plugging them. Refit the hoses over the duct taped connectors and tighten clamps (must NOT have any air leaks). Done.
Note: The AAV is tucked in behind the throttle body and is a mongrel job to get at. But it is possible, if you persevere.

AAR = Auxiliary Air Regulator
The AAR is critical for fast idle when engine is cold - don't muck with it. You can see if the AAR is working by peering into it with a mirror and torch. It is not serviceable (although I have read here of one pelican that had success tweaking it).

Decel Valve ??
Don't yet know why some here disconnect the Decel Valve. Works fine on mine and I like the way the revs remain high for second or two between gear changes for smooth shifting.

[dean]

I disconnected my first decel valve because it was blown. I like a car to go down to idle when I let off the acc pedal. It reminds me of the good old days when you let off the acc and the engine went to idle. I guess I am showing my age.

[targa80]

In your post you mention that after the car is warm and you shut it down for a while it is hard to start.
Question:
Does the starter have to be cranked several times for 10 seconds each time before the car starts after the car is warmed up and has been shut off for more that 10~15 minutes?
If the answer is yes this could be related to a loss of fuel pressure in the accumulator. A check valve in the fuel pump normally prevents fuel pressure drop by preventing fuel from returning from the accumulator through the fuel pump to the tank. If the check valve is bad you lose the fuel pressure in the accumulator and it takes a lot of cranking of the starter to keep the fuel pump on to rebuild up the pressure.

[Hladun]

1. Targa80 is right on the restart problem.
2. Sean Hamilton is right on the AAV vs. AAR. I've removed my AAV and another big benift is that my 78SC NEVER backfires on startup.
3. The decel valve also prevents the engine from stalling when you take your foot off. If your car stalls you need to reconnect the decel valve. Blown is right and hopefully he's not getting stalling.
4. CIS systems hunt during warmup. A range of 200 or 300 rpm for a few minutes is OK. My theory; too rich>engine slows down>less vacuum>leaner mixture>engine speeds up>more vacuum>too rich. Because of lower WUR pressure the system exhibts this hunting frequency.

[targa80]

In my car I have the O2 sensor and the lambda control. I had the hunting idle at startup and it took adjusting the mixture contol to eliminate it. With the lambda and sensor the control pressures are adjusted in the fuel distributor to lean or enrich the mixture to maintain the lamda reading around 1. with a misadjusted mixture the lambda system tries to control the mixture and causes the enrichment/ leaning of the mixture and that is what caused the hunting on my car.

[Superman]

Careful! I jsut don't want anyone to misjudge what part is what. My decel valve looks just about like the highlighted component above, and is located just behind the AAR, as shown in the picture. It is disconnected, and for good reason.

[Hladun]

Decel valves have three connections and AAV's have two.

[Sean Hamilton]

Originally posted by Hladun
Decel valves have three connections and AAV's have two.