Chrysler Repair: jerking/cutting out, 2000 T&C, 4 digit numbers, throttle positioning sensor

Question
my T&C is cutting out like something is killing the spark, briefly and repeatedly.  also if you are accelerating and then put it in neutral, let off the pedal, it will hold its original high RPM.  The MIL light comes on about 90% of the time but it does not show any trouble codes when i check the odometer "code 999" only shows up, then it goes through its regular checks.  Can the Throttle positioning sensor cause this? or would be be better to move to the cam/crank sensors?  I work at a shop doing rebuilds so electrical isn't my specialty.  any ideas?

Answer
Hi Robert,
What you tried to do by self-diagnosing was actually a test of the cluster itself. The 999 means there are no problems with the cluster.
To check for engine/transmission fault codes you use the igntion key:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch to odometer window see and 4-digit numbers preceded by a P which are the fault codes. Let me know and we'll go from there. Also mention which engine.
Roland