Fluttering Idle After Warmup

[itsjohnston]

2002 buick regal ls rough idle after warmup (shoots between 200 and 1200 rpm then dies) . New tps. New iac valve. New purge solenoid valve. New spark plug wires. New spark plugs. New MAF. New battery. Fluid levels good and good condition. New o2 sensors upstream and downstream. New knock sensor bank 2. New air filter. Checked for vacuum leaks. No codes stored or active or any other warning lights. New feul pump and filter. Injectors cleaned.

109k miles. No accidents

Crankshaft position sensor changed.

New Cat. What could cause this?