Idle problem

SWE930 · 12-30-2008, 05:53 AM

Hi!

I have had idle problems with my -77 930. Idle have been around 2000rpm. Today I found that the hose running from engine to brakebooster was broken in two. I figured this must be the problem så I plugged the end running to the engine just to see if this was the problem. When I started the car it was still running 2000rpm so I turned the car off. I left for lunch and when I came back I started the car again. This time with a nice 900rpm idle. I took the car for a drive and everything seems to be ok.
Just to verify that this realy was the problem I removed the plug while engine was running. I was expecting the idle to rise to 2000rpm again, but instead it started to run very bad ( no rpm increase to mention and it was kind of shooting flames or someting). Once the plug was back it runnes smooth and 900rpm.

Was this the problem or have the car fixed it self?

SWE930 · 01-01-2009, 12:45 PM

Today when I started the car again the idle is 1800 and increases to 2000 when engine getting hotter.

Any ideas what is causing this?

mark houghton · 01-01-2009, 01:23 PM

Sounds like maybe your AAV (auxilary air valve) is suspected of sticking open. Its function is to introduce air into the intake manifold when the engine is cold, to lean things out and cause a high idle. It has an electrical connection that feeds an internal heating element, which in turn eventually causes the valve to close once things warm up...resulting in the idle dropping back down to normal (engine heat alone will do this after awhile, but the element speeds things up). If you know that all your vacuum leaks have been corrected, then that is the first place I would look. You can take the entire valve out of the equation by disconnecting and plugging both air hoses (one comes from the intercooler which feeds air to the valve, and the other leaves the valve and goes to the intake manifold). Plug them both and you "should" have a very low idle in a stone-cold startup. If you continue to get high idles happening, then it's something else.

SWE930 · 01-02-2009, 07:18 AM

I have already checked the AAV. It has to be something else. Today I found a crack in the small hose to the distributer. I will buy a new one tomorrow and se if it helps.

willtel · 01-02-2009, 08:10 AM

Sounds like an air leak some place. Mine blew a rear intercooler seal this weekend and has been idling around 1400rpm since. You can spray starter fluid or a simmilar combustible around the intake and vacuum connections and listen for the idle to rise.

SWE930 · 01-04-2009, 12:15 PM

I found that the ignition timing was way off. I hade something like 25degrees BTDC at idle. I adjusted the timing to around TDC and it idles fine at 900rpm. I will adjust the timing tomorrow when I have a better timing light.

david3299 · 04:48 PM

I have a similar problem as SWE930. I have a 1987 930 with 70K miles. On my way home last night I noticed the car would idle at 2100 RPM with When I placed it in neutral.
This moring I checked for damaged hose found no problem. I checked the distributer wires and rotor and found not problem. Initially, when I started the car it idle at 2000 and as it warmed up the idle increasded to 2800 PRM. However, I noticed when I removed a hose (3/4 inch OD, I think it's the idle control valve) from right side of the air intake unit; the car would not start.
Any ideas?
Thanks in advance

930cabman · 01-04-2009, 04:20 PM

My '87 930 runs great with the exception of a high (1100 rpm) idle when the engine warms up. Idle is smooth, just a little high. Idle speed is around 900 rpms when engne cold.
Any ideas?
Thanks,

david3299 · 07:52 PM

I used a hose clamp around the hose (3/4 inch OD, I think it's connected to the idle control valve) to restricted the air flow by 50%. The idle RPM decreased from 2K to 1K.
Is this causing any damage? Those this means that my idle stabilizer valve is defective?

Porschephd · 01-06-2009, 08:54 AM

Quote:

Originally Posted by david3299

I have a similar problem as SWE930. I have a 1987 930 with 70K miles. On my way home last night I noticed the car would idle at 2100 RPM with When I placed it in neutral.
This moring I checked for damaged hose found no problem. I checked the distributer wires and rotor and found not problem. Initially, when I started the car it idle at 2000 and as it warmed up the idle increasded to 2800 PRM. However, I noticed when I removed a hose (3/4 inch OD, I think it's the idle control valve) from right side of the air intake unit; the car would not start.
Any ideas?
Thanks in advance

If you take the hose off and leave it unplugged the metering plate is not getting enough movement to start the car. If you fed it by hand it would probably run and idle at about 4K. If you close it off the car should idle, albeit probably low. The AAR Aux Air Reg is known for not closing all the way or the bi-metal strip inside going bad, the result is the housing has to heat up instead of it doing it internally and then closes. Makes a normal idle take for ever to be seen if at all. The other issue is the AAR which can stick open causing the idle to go through the moon or stay up sometimes and not others.

Helmsy · Helmsy's Garage

Can the AAR be serviced at all and should the gate return to the open position when cold and off the car or does it need power to open even when cold?

My AAR seems to be closed (slightly open) at cold and the car idles low until hot then it idles fine about 900rpm. The gate is not seized as I can move it freely off the car but it does not close completely.

Porschephd · 01-06-2009, 03:01 PM

I have heard someone repairs them but do not know who or have seen it. The AAR should be more open when cold and almost closed when off. The 12 volts supplies the bi-metal strip and the unit starts to heat up closing the door off to control idle. When you shut the car off it and it cools it will go back to an open position. So when you cut power the unit will go back open on its own.

You can bench test it by hooking 12 volts to it and seeing if in a 5 minute time it closes off, or at least all but a little slit. Some use a half moon shape and some have a slit as it closes and that remains the only open spot. That all depends on the year, Bosch number etc.

Helmsy · Helmsy's Garage

Thanks Stephen,

my AAR is off the car and closed all but for a little slit so I guess it's a paperweight now. I might pull it apart sometime and see if I can't do something with it.

I took it off the car and it idles fine once it's warmed up.

mark houghton · 01-06-2009, 06:09 PM

You can also make some adjustments by driving in a pin that's visible on the outside of the housing (I did so to increase the opening at cold just a little, since my cold idle was too low). But if memory serves me correctly you can only drive the pin one-way, so if you've gone to far...well, you've gone too far! I imagine a person could modify that pin (by drilling and tapping, similar to what's done for adjustable WUR's), to allow infinite finetuning.
Somewhere, on one of these forums, someone made mention of this technique. Damned if I can remember where.

Helmsy · Helmsy's Garage

I couldn't find the technique for the pin but this article shows the inside of the AAR and how to fix the resistance wire:

AAR Revisited