The n/a V6 will have an Idle Speed Control Stepper motor.
They are known for exhibiting issues and sticking, and/or burning out the coils so they don't work properly.
Firstly, if you've still got the engine management light, you'll want to retrieve the fault codes:
https://www.clubvr4.com/forum/showth...agnostic-Codes
The next best thing you can do is to do some logging of what's going on with a piece of software called "EvoScan" - the software and cable needed to do this can cost you under £30, and you will be able to perform lots of troubleshooting with this. This will also help you determine whether the TPS is working correctly.
https://www.clubvr4.com/forum/showth...ess-than-%A330
Do this before spending any more money :)