96 Volvo 850 NA 2.4 high idle, even after IAC swap

[JimBee]

A little history. A month ago, 3 miles from home, engine was hard starting and would hardly run. Up until this point, the idle had always been normal, ~ 750 and it has regularly started and run well. After 3 miles of the engine pitching conniption fits I finally made it home. Discovered the next day the IAC hose to the vacuum tree had come off.

I replaced the hose and starting has returned to normal and it runs great at road speeds. But the idle is high, ~ 1100, and at that idle I think it's running rich, even after warmed up. At a stop, after highway speeds idle is sometimes even higher, ~ 1300.

I tried swapping in a newish looking IAC and it makes no difference.

Around the city this is burning up a lot of extra fuel.

Here's a diagram of the system:
https://www.volvoclub.org.uk/tech/fuel_ ... Series.pdf

The only other component in the system that would seem to directly affect idle would be the idle control sensor. Now that I'm detailing this out, I'm wondering if all the foot-play on the accelerator needed to get me home might have damaged that sensor.

My code reader doesn't work so I'll take it to the parts store tomorrow to get them read. In the interim, any ideas?

[RickHaleParker]

Did you ever confirm that the IAC is working?

Other possible causes of high idle.

• 1. Fuse to IAC, would shut down the IAC.
  2. Air Leaks, the O2 senses the extra oxygen and ramps up the fuel.
  3. Malfunctioning Throttle, not fully closing.
  4. ECM Malfunction, brain damage makes for bad decisions

[misha]

Disconnect negative battery cable for about 10-15 minutes,perform re-learn procedure after re-connecting and see if things are improved.
I would say MAF or ECT sensor are bad if things are not imoroved after ecu reset.