another 560sl - year is 1987 - idle = 1500 r/pm

[blueshield11]

I have a 560SL from 1987. Idle is not okay at all: steady on 1500 r/pm, with cold engine as well as with warm engine.

Any idea what the problem can be here?

Thanks a lot !!

[Gurunutkins]

I am not that familiar with the 560 but it sounds like the auxiliary air valve is stuck open. I believe you have an electrical one, it should close as the engine warms up. easiest test is to grab the air pipe feeding the AAV (also called a cold start air valve) and just pinch it closed with your fingers or a vice grip with some cardboard between the jaws and the rubber pipe. if the engine slows down you have found your problem
cheers
barri

[blueshield11]

Originally Posted by Gurunutkins

I am not that familiar with the 560 but it sounds like the auxiliary air valve is stuck open. I believe you have an electrical one, it should close as the engine warms up. easiest test is to grab the air pipe feeding the AAV (also called a cold start air valve) and just pinch it closed with your fingers or a vice grip with some cardboard between the jaws and the rubber pipe. if the engine slows down you have found your problem
cheers
barri

Thanks for your reply but there is something I do not understand. I think you are giving me the right answer, but my english is not that good.

You say: easiest test is to grab the air pipe feeding the AAV (also called a cold start air valve) and just pinch it closed with your fingers or a vice grip with some cardboard between the jaws and the rubber pipe.

can you explain me a bit more. where is the air pipe feeding the AAV ? and where are the jaws and the rubber pipe?

thanks a lot,
Jan (The Netherlands)

[Gurunutkins]

Jammer Jan maar my duits in nie te goed nie!

I am unsure of the set up on the 560 but there will be a rubber air pipe coming off the throttle body or the air cleaner it will go to an electircally controlled air valve like the one in the picture (and forgive me if this is incorrect for your car) then the pipe will leave the valve and enter the block where you adjust the idle speed just after the idle speed screw.

what you need to do is pinch closed the rubber pipe going into the valve with your fingers or if they are not strong enough then clamp the rubber pipe between cardboard and the jaws of a vice grips or pliers so you stop the air entering the air valve. if you can block the air flow through the valve and the engine slows down then that is your problem.

the picture is of a AAV taken from a similar car to yours

I hope this helps

[Gurunutkins]

Jan I will send you a diagram of the car system if you PM me your email address but here is a small version the AAV is item Y6

[blueshield11]

thank you barri. I have received it and will go to work with it.

[MTUpower]

High idle on a m117 is not fun. There is also the black box about 2 inches by 4 inches near the rear of the motor. The box is plastic and when the top is removed you can see the soldering. Many times the soldering fails. It makes contact and idle is fine when cold then when it heats up the idle goes higher. Just heating up the solder will cause it to "reconnect". Sorry no pics or better description. On a w126 it's dead center behind the firewall. Don't know the location on a 560SL.

[blueshield11]

Thanks for your reaction. I did not have the time to work on it today.
I think I know what you mean about the black box with soldering. When I am correct it is the Idle Speed Control Unit, situated behind the glove box.
The high idle is not only when the engine is warm, it starts right away with high idle. But to be safe I will check the soldering in the Idle Speed Control Unit.

I get back with the results in a couple of days.

[KCM]

Check something simple first, the switch on the throttle butterfly. It signals when the butterfly is completely closed or wide open. There is a connector on the top left front of the engine with three wires. One is a common wire, one is for closed throttle, and one is for wide open. A simply continuity test between the common and closed wires (with the throttle completely closed) will determine if it is okay.

Had the high idle problem and it was just a bad switch. Went bad without warning.

[ctaylor738]

Something even simpler to check is if the throttle plate is closing all the way. Sometimes the linkage prevents this. Remove the air cleaner and unhook the linkage. If the idle improves, find where the linkage is binding.

[blueshield11]

Here I am again.

I have discovered that the Idle Speed Control Valve does not get power from the Idle Speed Control Unit. I have tried another good working ISC Unit but the result stays the same, no power on the Valve. When I squeeze the hose of the valve the idle speed reduces. So the problem is there, but I need some more help. (I have checked the fuses in the car on the passengers side and they are all good.)

[blueshield11]

Am I right that the ECU is controlling the Idle Speed Control Unit ?
And that the Idle Speed Control Unit controls the Idle Speed Control Valve?

thanks

[Gurunutkins]

Hi Jan, check the soldering in the Idle speed control unit. they are known to develop hairline cracks. Just touch a hot soldering iron to the solder traces to reflow the solder. Have you actually checked for 12v power to the ISCV? sometimes know good ones are not good depends on where you buy them. If you apply 12v to a known good one (usually center wire and then ground each of the other wires in turn (not together) then when one is grounded the ISCV will wind open and when the other is grounded it will wind closed. if that works then you probably do have a problem with the ISC unit and need to reflow the solder
good luck
Barri

[ctaylor738]

No. The idle control unit is separate from the ECU, and yes, the idle control unit controls the valve.

How did you test the voltage to the valve? It should be tested with the engine idling. You slide the connector back enough to get test probes on the two pins. You should see about 4 volts.

If you truly swapped the idle control unit and nothing changed, then the only two possibilities that come to mind are 1) damaged wiring to the valve, or 2) no power (pin 9) or ground (pin 11) to the control unit. You should check the fuse on the over-voltage protection relay, since that's where the idle unit gets its power.

[Gurunutkins]

sorry just saw Chuck's reply and he is right and I am wrong, its control voltage of 4 - 5 V not car voltage at 12v.