The high idle after driving is related to the speedometer quitting. You'll find it has set a DTC 311 for loss of VSS. The simplest cause of the sudden onset is often the wiring at the rear axle differential, where the vehicle speed sensor is. Your 900 has the same sensor as shown here on a 240.
But with the 900 comes more difficult issues in the speedometer itself, as the corrosion from leaky electrolytic capacitors destroys circuit foils. See the 7/9 FAQ. Have your mechanic see the FAQ list.


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Art Benstein near Baltimore
“Expertise in one field does not carry over into other fields. But experts often think so. The narrower their field of knowledge the more likely they are to think so.” – Robert A. Heinlein
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