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Thanks for posting
The coolant temp sensor is a possibility, the most common cause is a sticking IAC valve, I know it was cleaned but did you check to make sure it's not hanging up? I assume there is no check engine light. Make sure the vacuum hose on the center port on the iac is not loose or leaking, It may be necessary to replace the iac valve, sometimes cleaning it does not take care of the problem.
Beside the two coolant hoses there is one vacuum hose port coming from the intake plenum, double check to make sure it's connected. Can you get the current code for me?
I just checked, the 1999 doesn't have the vacuum hose.
Thanks, the EGR code is for insufficient egr gas flow, it won't cause the stalling issues. If it's an evap code it may have something to do with it possibly a purge vsv malfunction, see if you can get the present code and let's go from there.