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Re: I'll try resetting the idle... (archive)

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Posted by Rod... on November 18, 2000 at 07:28:39:

In Reply to: I'll try resetting the idle... posted by JamesM on November 17, 2000 at 09:37:33:

Thanks for the detail. But could that cause the engine to "hang" between shifts? It doesn't do it all the time. I'm going to try resetting the base idle.

I'd assume you have to set the idle CO by tapping into the exhaust manifolds. Who would have this tool? Also, how much is a Fluke these days? I remember my dad paid several hundred for his 77 a while back.

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88 M5
88 M3
83 535i

It could.

Also check the throttle switch. If the throttle switch doesn't close reliably the engine RPMs will not drop quickly. A normal function of the DME(coast-off) is to shut off the injectors when the engine speed is over 1200 RPMs with the throttle closed. Also the throttle switch is what sets up closed loop idle speed and when the throttle switch is open the idle control valve will remain wide open.

A Fluke 88 (automotive DVM)with RPM, Dwell, duty cycle, pulse width and Min, max & averaging functions can set you back alittle over $300(discount price).
Good tools usually cost more than I want to spend but have always proved to be cheeper than paying for the labor of others.

The Motronics on the S38B35's do not have an engine check light, internal diagnostics or flash codes. The CO is set and checked by monitoring the O2 diagnostic output with an integrating/averaging meter on the diagnostic connector, as I indicated. This is a BMW procedure. An exhaust gas analyser would only be necessary if the engine is missing firing or for other combustion/cat converter diagnostics. BMW has an integrating meter that is used for setting the AFM CO with the Motronic version 1.0 units. The Fluke averaging DVMs (87 & 88) will do the same job as the BMW integrating meter. You can use just about use any type of volt meter to monitor the O2 sensor cycling(0-12 Volts) at the diagnostic connector, which is the primary indication of the correct CO setting. With a little electronics knowledge, a capacitor and a resistor, one could fasion a simple integrator for an analog or digital voltmeter.

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