96 Regal Idles High once in awhile

It had a Throttle position sensor low voltage code in history- so I replace tps. But still it will idle 1400-1500 rpm after start up once in awhile- the fix is to shut it off and restart, now idle is normal- below 1000 rpm anyway. What gives- I've cleaned IAC and throttle body cavities and replaced IAC- still problem persists- about once after every ten starts....no codes now of course.

If it idled high all the time, I'd say it was a vacuum leak- but most of the time it is fine...just annoying once in awhile.