Idle speed in park on my 1998 Volvo S90 is running around 1400 RPM. Four questions:

1. What is the correct idle speed under no load?
2. How is the idle speed adjusted?
3. Where is the adjustment made?
4. DIY or should I take it to a mechanic?

 

Hah! The solution was rather simple. The idle speed was erratic due to a faulty idle air control motor. Once that was replaced, the idle speed was considerably higher: 1400 rpm when the engine was warm, 1100 rpm when cold. It turns out that the entire control assembly had shifted forward in it's mount. Loosening the retaining bolts and realigning the unit with the index marks dropped the idle speed back to 750 rpm; right where it belongs. Cleared the "check engine" light, and all is well.

 

The bosch idle speed control is rebuildable. The one on the volvo looks and works like the ones I have on other cars.

They eventually get clogged with oil tar and don't turn easily. Bosch say don't clean it but I've cleaned out every one I've had and this has not caused any problems (I put 30k miles on one I cleaned in 2007.)