Hey there I have an Evo 4 and 6 months ago snapped my timing belt and had to do the engine head. The battery was disconnected for 6 months straight and now I have it running again however when it's idling, when I first start it it sits at around 1000 and then when it starts to warm up it will bounce between 1500 and 2000. Every now and then it will jump to 2500 and stay there till I shut the car down for a while. Some people have told me it's just me ECU remapping itself because the battery was disconnected for so long but I feel like it's something different. Any ideas of what it could be or tests I could run?

Thanks

 

clean your intake manifold and throttle body really well, gunk buildup will cause this, also, the iacv has a gasket, if that is bad it will also fluctuate.

 

Check the iacv it maybe stuck/sticking

 

Sounds like ICAV to me too. I wouldn't buy an Evolution ICAV though, Dodge makes one that is almost identical that I've been using for years and it's a lot cheaper. $60-$70 maybe?

 

Any updates. Was your problem solved. If yes then give details what was the issue.
Thanks