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Mike Feinstein
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Idle adjustment-964

My 94 964 idles at 1000 rpm. It is stock except for a Mass-airflow system with a K&N cone (bought it that way. . .would have preferred stock). How can I adjust the idle speed down to about 750?

Thanks, Mike
Old 01-10-2001, 12:50 PM
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Nickshu
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Mike,

The idle speed is not adjustable on a Motronic system like your 964. It has a throttle which closes completely sealed. A hose then goes from one side of the throttle to the other with a device called an AIC motor (also known as an idle regulator valve) midway in this hose. This valve is controlled by the FI computer and opens/closes as needed to maintain a factory set idle speed regardless of load or whether the A/C is on or off.

Some of these systems have a "Limp Home Mode" that cause the car to idle at 1000 or 1200 if the AIC motor should fail. It is possible that yours is not working, or the aftermarket intake you have is somehow tricking the computer to raise the speed. If you find the AIC valve at the throttle body, you can tell if it is working by listening to it when the car is running. It makes a buzzing sound. Also, it will often buzz for about 5-10 seconds after the car is shut off to reposition itself to an open position for the next time you start.

Sometimes I think it is rediculous that I know more about the pulsed injection systems like Motronic than I do about the CIS system in my 911.

Anyhow, I'd start there.

Best of Luck,
Nick.

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__________
Nick Shumaker
1982 911SC Coupe

[This message has been edited by Nickshu (edited 01-10-2001).]
Old 01-10-2001, 04:09 PM
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Mike Feinstein
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Nick:

Thanks, I identified the module and, although I can't really hear it over the normal engine noise, I simply unplugged the wire harness that feeds it. The idle speed dropped to about 400. Soon as I plugged it back in, the idle jumped back to it's (ab)normal 1000. This tells me that it is operational (?). I notice in the end of it is a small round opening. . .could this be some kind of adjustment access? Perhaps it's just wishful thinking.

Thanks again, Mike
Old 01-11-2001, 11:57 AM
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Nickshu
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Mike,

I don't think that that hole is an adjustment, but Im really not sure. As far as I know, this system is not adjustable.

The computer has memory, so disconnect it, then start and drive it a little to reset the memory, and make the computer realize that there is a wierd signal from it, then see how it behaves.

Sometimes the voltage/resistance from the idle regulator stays normal, while the valve itself will bind. This can trick the computer to make it think that it works, but it doesn't.

You may also want to look for any vacuum leak that may cause it to behave like this.

What did it idle at prior to this? Did the high idle start when you made the modifications?

Just wondering.

Nick.

------------------
__________
Nick Shumaker
1982 911SC Coupe
Old 01-11-2001, 12:08 PM
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Mike Feinstein
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Nick,

Do you mean I should disconnect the module as I did in my brief test? Couldn't this make it worse?

The mods were on the car when I bought it last summer. . .has been idling at 1K since I bought it.

Thanks, Mike
Old 01-11-2001, 12:27 PM
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Kurt B
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I also have an idling problem on my 84, and the problem is that on startup, pretty randomly actually, the idle with surge up and down sporadically. Now if the car is started and driven, this surging never rights itself, even after the car is warmed. However, if you let it "find itself" by letting it surge around for 45 seconds to one minute, it will idle a bit high.
Let me add, that to correct this, I DID replace the idle stabilizer, the part you're talking about now, that joins the air box and intake manifold, but this did NOT correct the problem even slightly. In fact, I'm at a loss as to where to hunt around now.
If I do unplug that stabilizer, the car just acts worse...so I don't think that therein lies the problem.


However, if he's got a motronic, he can adjust his idle pretty easily, but you need a piece of wire to short out the circuit (2 and 3) connectors in the engine compartment....details in the haynes manual anyway. Then you can adjust the idle with a screw driver, once the circuit has been shorted.

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Kurt B
1984 911 Carrera Cabriolet
75 914 1.8

[This message has been edited by Kurt B (edited 01-11-2001).]
Old 01-11-2001, 01:00 PM
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Nickshu
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Ok, a couple of points:

1.) Mike: Yes, I do mean leave it off for a while. It will idle slow, but see what happens and let me know. Also, whats wrong with idle at 1000?

2.) Kurt: what you are experiencing sounds to me like a classic bad air mass meter (flow meter). If the idle regulator was bad, then it would stall, or not idle at the right speed, but it would not idle up and down as you describe. You can test your flowmeter with an ohm meter between 2 of the pins (you'll have to look it up since I don't recall which pins or what ohms should show).

Also, what you are describing about adjusting the "base idle" with the computer grounded out is true for your DME engine, but not the newer style of Pulsed injection like Motronic. This was probably changed around the 89-91 model years.

Hope this helps yall.
Nick.


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Nick Shumaker
1982 911SC Coupe
Old 01-11-2001, 04:33 PM
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Kurt B
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Wow Nick, you really do know your shister. Thanks for the advice, I'll check it out. (Then I gotta check on the heater too, whee, lots going on)

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Kurt B
1984 911 Carrera Cabriolet
75 914 1.8
Old 01-11-2001, 05:25 PM
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Mike Feinstein
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Nick,

You raise a very reasonable question. . .1000 is OK with me but I thought that normal idle speed was 700-800 and thought, if it wasn't too difficult, I'd tweak it a bit (I've gotten in trouble with this approach in the past though . BTW. . .the tach shows a fairly regular 50rpm bump every few seconds. Really not that noticeable but probably not right. Any ideas?

Won't get a chance to try running it disconnected until this weekend (traveling). I'll let you know what happens.

Thanks again for your advice.

Mike

[This message has been edited by Mike Feinstein (edited 01-11-2001).]
Old 01-11-2001, 07:01 PM
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Nickshu
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Mike,

The bump you see is probably the o2 sensor doing its job. It causes the system to cycle rapidly between rich and lean to keep the emissions down at idle. I wouldn't be concerned about it. Also, check the specs for your car about the idle speed. I would be happy with 1000 as long as it is quiet, does not vibrate, and is at least close to the spec. Since you have some intake mods, and if the car is not stalling or idling erratically, I would leave it alone.
Best of Luck.
Nick.

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Nick Shumaker
1982 911SC Coupe
Old 01-11-2001, 09:28 PM
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Mike Feinstein
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Nick:

Ha! That's probably the best advice yet. Perhaps I should just enjoy the ride. One other question on the topic though. . .When I depress the clutch while preparing to stop, the engine speed will drop quite low, rebound, drop and rebound a couple times before stabilizing at 1000. It never stalls though. Is this normal behavior under the circumstances?

Thanks,
Mike
Old 01-12-2001, 05:51 AM
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Mike Feinstein
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Nick,

Gave it a try. . .disconnected the idle reg valve and the idle speed dropped to about 250-300 (was suprised how smoothly it idled at such low rpm). Drove for about 1 mile, 40-45 mph, 4th gear. Hooked it back up and it went right back to 1000-1050.

Oh well. . .it's never that easy!

Rgds, Mike
Old 01-12-2001, 12:27 PM
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Nickshu
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Mike,

I would say that the idle drop you experience is probably normal. Sometimes the idle regulator has to "catch" the engine speed and adjust to stabilize the idle. This may also be affected by the big flowmeter you have. I have 2 cars with pulsed injection systems and the both do this, even with all factory settings and everything working correctly. If it never stalls, and rapidly reaches a stabile state, then I would not worry about it.

It sounds as if your idle regulator is working ok, so I would go with my prev comments about just leaving it as it is since it sounds like it functions well.

Best of luck.
Nick.

------------------
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Nick Shumaker
1982 911SC Coupe
Old 01-12-2001, 12:34 PM
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Old 01-12-2001, 12:34 PM
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