CIS idle speed

[rgmrgm]

My 83 SC idles a little rough on a cold start up but a few bumps of the throttle smooths it out at 800 - 900 rpm. It maintains that idle speed through normal driving until it gets hot after a long drive then the idle goes up to 1100 - 1200 rpm and stays there. No A/C no cat otherwise bone stock. What causes this increase?

[T77911S]

for some reason the mixture could be wrong when cold(even warm but it is close enough that it runs ok). probably too lean, then as it warms up the mixture gets closer to being correct. someone may have adjusted the idle for a cold idle instead of a warm idle.
also, the aux air reg (AAR) may be bad. that raises the idle only when cold.

start with air leaks and control pressures.
also check the inlet screen on the warm up reg (WUR). if it is blocked it will raise the CP.
I would also check for power to the WUR and AAR.
AAR could also be stuck closed

[gazzerr]

The AAV might be leaking too. You can give it a 1mm squeeze in the middle with a couple sockets in a vice. There was a factory update fix out about that.

[strictly]

Originally Posted by gazzerr

The AAV might be leaking too. You can give it a 1mm squeeze in the middle with a couple sockets in a vice. There was a factory update fix out about that.

very intresting. Do you mean put a socket down the internals of each end that goes into the rubber pipes and try and squeeze the moon bit and the static bit a bit closer (i.e 1mm)?

[Bob Kontak]

Originally Posted by strictly

very intresting. Do you mean put a socket down the internals of each end that goes into the rubber pipes and try and squeeze the moon bit and the static bit a bit closer (i.e 1mm)?

The AAR has the moon thingie.

The AAV is one of the gold space ship things. Not the one closest to the passenger rear tire. That is the decel valve.

To do the vice trick you remove the part and work the squeeze on the bench.

AN alternative I have never tried but watched it being performed is to snake a set of channel locks back in there and squeeze in the middle of the space ship.

Worked like a charm (my 81) but it was an experienced P car mechanic that did it. Vice sounds way safer for us DIY guys.

Bummer that it will take a lot more time but I bet gazzerr is right.

[gazzerr]

^^ Like Mr K, said. If you PM me I'll send you the Porsche update doc on it.

Yep you squeeze it in the middle of the gold space ship by 1 mm. The sockets cover and prevent damage to the ports.

[gazzerr]

Here's the TSB on it:

['78 SC]

I used a vise so the amount of squeeze is easy to control.

The smaller hose goes to a hand pump and the other connects to an air supply. These let me measure the vacuum at which the valve opens. By making small adjustments and rechecking the opening pressure I could sneak up on the setting.

[gazzerr]

^^ there you go that's awesome.

[gazzerr]

Just to clarify I meant the Deceleration Valve or the Vacuum Limiter as Porsche calls it. Not the AAV. Apologies for the confusion. The picture above by '78 SC clearly shows the component that i am talking about.

[strictly]

ahhh very intresting. I actually have a PDF with all of the technical bullitins, i just haven't yet had time to read them all, good to know, thanks for clarifying!!

Luke

[Bob Kontak]

Originally Posted by gazzerr

Just to clarify I meant the Deceleration Valve or the Vacuum Limiter as Porsche calls it. Not the AAV. Apologies for the confusion. The picture above by '78 SC clearly shows the component that i am talking about.

Thanks for the clarification. I was giving incorrect advice as well with respect to AAV.

Decel valve is easier to remove.

[gazzerr]

There's too many gold colored donuts under there .

[strictly]

I am having a similar problem (i'm also chasing other problems), but specifically on my AAV

I have tested mine on a mitivac (its for a 78 SC) The valve opens around 8 in Hg, but when I remove my figure will only hold vacuum for say 5 seconds, at 9 or 10 in Hg, it holds vaccum with my fingure removed for about 20 seconds, does this sound like its working or not working?

When it loses vacuum, it is instant, not a slow drop

[gazzerr]

Hey Strictly, on the AAV I think it's actually the engine vacuum that keeps it shut. It gives you a puff of extra air via the bypass to the airbox at startup then the engine vacuum should keep it shut. I think a small leak is ok because the constant engine vacuum should keep it shut. I'd say once it leaks down without that constant vacuum it's popping open. That might be normal.

[strictly]

ok gaz, thanks for the advice. I'll consider it working for now.

L

[gazzerr]

No worries. I believe there's a thread off this one that talks about testing the AAV and most of the other vacuum operated components.

CIS Troubleshooting for Dummies

[strictly]

gaz,

good post buddy, thats a really cool link, im reading!

[gazzerr]

No worries, Tirwin is the one to thank for that one. One of the "golden" threads.