My M103 (W124) idles fine and runs smoothly for the most part. But it has what I describe as flat spots in its acceleration curve. Under load (not necessarily even WOT, which I don't do much of), there are subtle losses of acceleration that give it a feeling of very slight momentary loss of power. I'm not talking about anything dramatic, it's very subtle, but it can be detected behind the wheel. No CEL, no codes.

Regular maintenance has always been meticulously performed since new. Recent servicing included fuel and air filters, correct copper non-resistor plugs, new OVP, fluid replacements always. Three times a year it gets a bottle of Redline injector cleaner spread out over 2-3 tank fulls. Fuel pump is original.

Hauled out the multimeter and tested all the electrical components in the CIS-E system. Pressure was not tested, nor was duty cycle. Otherwise, all of the FSM diagnostic tests were conducted. All but two tests were well within specs. The two problem tests are:

1) Throttle valve switch (S29/2): Measuring at the KE controller (N3) coupling, depressing throttle should take resistance from <1 Ohm to infinity. Instead, it reads 38.7K Ohms with throttle depressed. The same test at the connector (S29/2x) is supposed to give the same result, which it does, but once again at only 38.7K Ohms rather than infinity. That's the first problem with S29/2 (its idle speed reading). The companion test for full load speed also gives anomalous results. Instead of infinity going to < 1 Ohm upon accelerator depress, my result is infinity at all times. This is true both at the CIS-E coupling and at the S29/2x connector. The wiring tests fine at 0.2 Ohms. That tells me that the S29/2 switch is bad. Right?

2) Air flow sensor position indicator (B2): Measured at the B2 coupling, I get 2.4K ohms, against specs of 3.6K - 4.4K ohms. Slowly deflecting the air flow plate is supposed to cause resistance to rise continuously up to half deflection, and then to drop off again. My result is infinity at all times during deflection. Here, too, the wiring in the circuit back to the CIS controller tests fine at 0.1 ohms. I interpret this as a bad B2 sensor. Is that right?

My question: are these two components (S29/2 and B2) likely to be the cause of my acceleration "flat spots", or is it something more mechanical, like the camshaft, or even a compression problem? Thanks for wading through a long description.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

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