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Surging Idle 95 S320, Where is overload relay??

Greetings,

My 95 S320 has recently developed a surging idle. I read through previous posts and tried a few things but problem persists.

At idle, in or out of gear and hot or cold, idle surges between

500-700 rpm with an occasional peak to 1000. I disconnected the MAS but noticed no change at all. Voltage at idle with A/C on is about 14.10. Plugs and coils changed last year and car has about 80K miles.

I read about the "overload relay" and how that should be checked first. I looked behind the fuse box and did not see any relays with a fuse on the top as described in previous posts. Is it different or located elsewhere on this model?

Any ideas would be appreciated!! Thanks,

Bob

Reply to
Bob
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There is no over voltage protection relay as on older models. This is taken care of by a more modern power supply design.

The idle speed is controlled by the same circuit as the cruise control, which means that the throttle position is controlled by an electric motor.

There could be varios reasons for the surge. Here are some:

1) The throttle position is monitored by a potentiometer within the same unit with the electric motor. If the motor or the potentiometer is mechanically loose, or if the potentiometer is defective, the idle will surge.

2) If the throttle is sticking, it will surge

3) If the mixture is too lean it may surge

In any case, the surge is probably due to too slow reaction in the idle control loop (the engine reacts too slowly according to the ECU's commands), or there is something else wrong in the loop (f.ex. loose mechanical connection).

Bob wrote:

Reply to
Jens

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