380SEC idle problem confusing me-help please

Hi, I bought a Idle speed control unit My car is 1983 380SEC the unit part nbr is 002.545.33.32 and it is remanufactured.
Prior to installing, and as instructed to insure no damage to the idle control unit, resistance was checked to the idle valve. Resistance ohm reading between pins 1 and 5 was 10.4 with instructions saying 10 ohms plus/minus 2. The car started and idled at about 800 RPM therefore I assumed it was fixed. The next day it was back to its Hi-idle at startup.
Next, I replaced the idle valve. I read on this forum that sometimes they stick. Neither the new or old valve will click when turning the key on or off. It does click when jumping pins 1 and 2 - 5 and 4 per the engine manual. Intermittently now the car starts and idles at 800 RPM which is something it did not do before replacing the idle control. Most of the time it starts and idles at 1200 to 1300 RPM . With the prior controller it usually started an ran around 1500 RPM. With the rebuilt controller the car starts at 800,1250 or 1500 RPM and as the car warms the idle will increase. When starting off at either 800,1200 or 1300 RPM it will warm and to around 1500-1700 RPM.
Is the new Idle control unit bad or is the new idle control valve bad?
Note: both the new and old Idle control valve will click with battery power. With the ignition on there is power at pin 2 a good ground at pin 4. There is no power at the idle control valve, but the pins 1 and 5 show a good connection to the idle control valve. Thanks for any help. Mike
See my SEC and Speedster at www.356regestry.org in the members cars section.


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1983 380SEC
1955 Porsche Speedster

[stevebfl]

There are a number of possibilities. To test properly you should monitor the signal to the idle valve with a multimeter or scope set on duty cycle. The valve is pulsed at a constant frequency with a variable duty-cycle. The system will go to between 70 and 80 percent (on) duty-cycle before it resets itself and starts over. The idea is that with the proper air going through the normal idle a midrange duty cycle will occur. If too much air is getting in due to partially open throttle or vacuum leaks, the system will put the valve in max duty-cycle trying to shut down the air to lower the speed.

So the key here is to see if the duty cycle is maxed out. If it is then the system is doing its best but the engine is getting too much air somewhere else. We use a smoke machine to verify the integrity of the manifold/vacuum systems.

Another thing to check is the throttle switch. The engine goes to a fixed open state everywhere but at idle. If the throttle is gummed up and not fully closing both things will happen: too much air and a fixed response.

I would also verify the power and ground circuits (for the idle controller) when the system is functioning (or mal functioning). I'm not sure but the Overvoltage Protection relay may power the idle controller and be suspect.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

[Benzmac]

It sounds as if you had more than one problem...One masked by the other.

You should check the throttle switch.

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Benzmac:
Donnie Drummonds
1992 500E (very soon I hope
1981 280GE SWB
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
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