The RPM gauge is flying up and down and the engine is surging on idle. Initially, it backfired and stalled on a warm start. Gave it a little gas and it restarted but that's when the surging started. Both crankshaft and throttle position sensors have been replaced. Any ideas, please?

What motor? How many miles?

How long has it been since a full tune up?

When my car was surging, stalling and having a hard time finding idle, the maf sensor was faulty. Try unplugging it and see if it runs better.

Sounds Like A Mass Air-flow Sensor Problem. Easy Change, But Expensive Part. Had Same Problem In My 2002 Gp. Check Engine Light Did Not Display But Code Came Up On Diag. Check. Have It Scanned To See What Comes Up.