Revs in park. and a bigger question.

1998 Venture with 127K miles. New plugs right after successfull intake manifold gasket repair at 118K. Has run well ever since, till today.

I pulled into a parking space, put it in park, and then the engine revved up to about 1200 rpm. Shut it off and turned back on. Still revved. Shut it off and went shopping. Came back out 15 mins later when my youngest acted up in Target, sat at idle while my wife finished shopping for another 25 minutes. It sounded fine. (Watched a lady get a ticket for parking in a fire lane. Classic. :lol: )
As I was leaving I noticed the "Service Engine Soon" Light was on. Not flashing. Just on.

So then I drove another 5 highway miles to the grocery and left it idling while I went in to pick a few items. My wife shut off after 5 more minutes of higher revs (1200ish).

The basic question to all is, what is the cause? How to fix?

Bigger question and discussion topic-
I bought some STP injector cleaner and fed it to the tank. Figured I would start with the cheap fix.
The bottle claims "Made with Jet Fuel" which would make the random buyer think it is nitro or something. I know Jet Fuel is one step below Kerosene, but higher BTU per Gallon. "Carrier for active ingredients" is in small letters on the bottle.
The cleaner even smells like kero.
Has anyone used Kero as a cleaner or treatment? Say, adding a quart to a tank of gas? Are the "active ingredients" really what does the work, or is it the Jet Fuel?

You need to get yourself an OBD-II code reader, as that should tell you exactly what is causing your idle problem. There are some really cheap ones out there (around $30), but they do not allow you to clear the codes. I paid around $150.00 for mine which has all of the features any DIY would need, plus a good sized book with all the code definitions. It has been worth every penny.

The fuel treatment worked.
Problem solved in less than a tank of gas.

Still want to know if anyone has used Kero alone to treat fuel, or is it REALLY just a carrier for active ingredients.

You need to get yourself an OBD-II code reader, as that should tell you exactly what is causing your idle problem. There are some really cheap ones out there (around $30), but they do not allow you to clear the codes. I paid around $150.00 for mine which has all of the features any DIY would need, plus a good sized book with all the code definitions. It has been worth every penny.
I've been looking at one at Autozone that they got in recently for $79.99. It seems to be a good one for the DIYer also. I just love technology today, you wait awhile and the prices will drop.