Why does your 1999 Isuzu Rodeo idle high when the engine is cold it continues to run cold even after warming unless you reset the IAC unit it then runs fine until it sits and cools down all night?

Answer 1

I have a similar problem...but doesn't answer your question. Perhaps some one in the "know" will answer both our questions.

My 98 Isuzu rodeo will start up fine in the cold with a high idle but will quickly settle down when the engine warms up. Once the engine is warm it has a difficult time restarting. It will often fail to restart when warm on the first try. Always on the second try, the idle will hunt for a brief couple seconds and then find balance. The car runs great once balanced and has no other issues.

Here's where we're the same. Resetting the IAC can preempt this problem.

The SUV is in a "open loop" until the O2 sensors are warmed up so all idle problems stem from a couple sensors or fuel side problem. It could be a vacuum issue or EGR issue but in my case I tested both and all is fine. I get no codes. I may need to keep throwing sensors at it until it's gone. The MAP and Fuel pressure sensors are my next victims.