Could my intake manifold have a crack in it to make my 1997 Cadillac deville idle to high
That is a possibility yes. Check for loose or cracked vacuum hoses too. Use some spray carburetor cleaner and spray it on suspect areas. If you notice an immediate change in engine speed then you have found a leak.
i try all that at first, but the engine never changed speed, i changed the tps and nothing happen, after a few hours it will mysteriously idle back down for a few hours then it will go back up to 2000 to 2800 rpm
Checj to see that your temp sensor is working correctly . low temp will cause high idle if not at operating temp. Also check coolant.
my coolant sensor is brand new, i just put a motor in this car, coolant level is full, it still idles very high at 200 degrees, then occassionaly it will just ease back down, or you can cut the engine off and restart it will idle at about 1500 for a while then ease back up
Sounds more like a sensor problem than a leaking manifold. The manifold problem typically would not cause the engine to "cycle" the RPM's up and down.
i have replaced the tps the coolant temp sensor what else do you recommend, the check engine light is not on
Looking for a Used DeVille in your area?
CarGurus has 2,392 nationwide DeVille listings starting at $1,600.
Search Cadillac DeVille Questions
Cadillac DeVille Experts