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Re: Symptoms: (archive)

[ Follow Ups ] [ 5-series (E34) Message Board ] [ Msg. Board FAQ ]

Posted by paul on October 26, 2000 at 16:34:22:

In Reply to: Symptoms: posted by Chris on October 26, 2000 at 16:12:05:

I think your analysis is correct. Since it's intermittent have you tried wiggling wires and connectors during the low idle senario? Perhaps the idle control valve is sticking. I would check further on the crank sensor, it could still be the culprit without necessarily triggering a fault code of its own.

1994 530ia

On a warm engine, the idle periodically hovers around 500, with Check Engine illuminated. When idle is in it's normal range, everything is fine.

No problems while driving - no hesitation, no check engine.

If I press on the accelerator while idling, the check engine light shuts off. Once it returns to idle, it will eventually illuminate again.

Using the Peake Reset & Code Scan tool (R5-FCX), I get the "Lambda control #1" and "Lambda Control #2" errors (lean/rich control stop). One lambda sensor brand new, the other has less than 10,000 miles on it.

I called the dealership service dept, and they were the ones who suggested testing the crank/rpm sensor. I've also seen posts in the archives that suggest the same thing.

Regarding small intake leaks, my understanding is that the Bosch system used by this vehicle is a 'closed-loop', adaptive learning system. The bosch ignition system doesn't use the AFS exclusively to determine injector duration, rather, uses it in conjunction with the Lambda sensor readings and others, and adjusts injector duration accordingly to keep the proper air/fuel ratio, called 'Lambda'.

For example, if there were a small intake leak, the system will run lean. However, the lambda sensor will 'sense' the leanness in the exhaust, and the computer reacts by injecting MORE fuel to compensate for the leak, thus bringing the air/fuel ratio back to it's ideal level. If, after several tries, it cannot bring the ratio back to ideal, Lambda control #1 & #2 will be stored, and the check engine light will illuminate. The computer should be able to handle a leak as long as the leak isn't too big.

Thanks again!

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