Has it ever been tuned up ie. Plugs, wires or boots, filters, and injection cleaning? Check the tire pressure, under inflated tires are the #1 cause of poor mileage. Also consider fuel quality and additives that don't contribute to combustion. I hope this helps, Take care.
You need a professional mechanic with a scanner. Never drive a car with a flashing check engine light except to get it off the road. Flash = serious issue.
LUCAS is one of the best sold at any parts store. And is made for just that. Read MNFCT recommendations and directions for uses on EGR, PCV and intake manifold build up.
Still think ot vacuum related .This will push the revs up sky high .Get a good cigar and pulloff a vacum pipe .Take a good puff on the cigar now puff the emoke down the vaccum pipe .Now do you know what your looking for .You got it ,,, smoke ,,,,than you have found the leak.Thats if you have one ..Can you get a obd check it will tell you what it is ..Thermostat removal wont change the engine revs
you may want to look at your Catalytic / O2 sensor(s) Watch this video to learn more about how the O2 sensor works and what is required of the O2 sensor for it to work in the vehicle. https://www.youtube.com/watch?v=DvKZ2GDYEz4 Note: The vehicle in this vehicle does not compare to your own since the sensors on your vehicle may not be under your hood but may be on your header exhaust or you could have one on the lower exhaust pipe and one on the upper exhaust / manifold.
Sounds like the transmission interlock switch for the starting circuit is malfunctioning. It keeps the car from starting in gearshift position but park.
The interlock switch can be temporarily jumped out of the circuit to test if this alleviates the starting issue.
If it does, get repaired immediately since this is a safety feature.
