High / Low Idle

I have a 98 with a 4.2 V6 engine. I have 85000 KM on it. Truck runs great no issues what so ever except for idle on a cold start. The engine revs up and then idles repeateadly. I have had some issues with engine ping. Using better fuel solves that or recently I have discovered using ethanol enhanced gasoline does the same thing and is about .08 cents a litre cheaper than premium gasoline.

Sounds like a IAT solenoid. They only take a couple of minutes to replace and cause all kinds of idle problems when they go out. I wouldn't hesitate to try one.