you probably have to 'program' the immobilizer:
Here's the GT200 workshop manual's take on it:
Quote:
When the ignition system is not coded, the engine can be run at a maximum speed of 2,000 rpm. Any attempt to rev up causes the engine to misfire.
To code the system, set the emergency cut-off switch to the «RUN» position and use the MASTER (brown) and SERVICE (black) keys as follows:
- Insert the MASTER key; turn the ignition switch to the «ON» position for approximately 2 seconds (strictly between 1 and 3 seconds) and then turn it back to the «OFF» position
- Insert all the SERVICE keys available in succession, each time turning the ignition switch to «ON» for 2 seconds
- Insert the MASTER key again and turn it to «ON» for 2 seconds Note: The time needed to change keys must not exceed 10 seconds.
Note: A maximum of three SERVICE keys can be programmed within the same coding session.
It is essential to observe the sequence and time limits as described above. If at any time during the programming session these are not observed, the procedure will have to be restarted from the beginning.
Once the control unit has been coded, an unbreakable relation is created between the control unit and the MASTER key transponder.
You can find a link to the workshop manuals here:
Workshop Manuals