Hi Laurens Since you don't have Protune access, I'd suggest getting a voltmeter on to the throttle position sensor wires. I have adjusted it this way and it cured various odd symptoms. I can't honestly remember the voltages that you want to see at closed and fully opened throttle, but you have a working one to compare it to. In theory it's a sealed, calibrated unit but in reality it's easily adjusted, though you might have to remove some silicone sealant that covers one of the adjusting screws. The other thing that can cause issues is the connectors on the TPS and on to the idle air control valve, if they have been disconnected they sometimes don't quite connect together properly, or a little bit of corrosion can form on the contacts and it can be as simple as disconnecting and reconnecting them a few times to clean the contacts and get things working properly again.
