Malibu Starts Hard When Warm

I have a 2001 Malibu that starts easily when cold but when it is warm, up to 4 hours after turning if off it is very hard to start. It will try to start then stall and then I eventually have to floor it to get it going. A big cloud of smoke come out of the tail pipe but then runs at a high idle. Sometimes I will get a 3000rpm idle and then after about 30 seconds it will idle right. I have a new fuel pump, a new Charcoal canister, a new vent valve solenoid, a new fuel pump relay, a good battery and a good starter. I also checked the fuel pressure regulator and no gas leaks out. Also have had a full tune-up. Any suggestions?

This problem turned out to be the Engine Coolant Temperature Sensor

Your system may be trying to flood? Were the 02 sensors part of the tune-up? Any applicable trouble codes? Some of the national brand autostores will check codes for free.

If the fuel pressure drops like a rock right after you turn the key off, you have a fuel pressure leak. The pressure should hold for a bit.

When a car is cold, you want the fuel mixture to be rich on startup......when a vehicle is warm, you want the fuel mixture to be lean on startup....

O2 sensors have nothing to do with startup.....

I would suggest getting a gauge on the fuel system to see what the pressure is and if it holds.....

Would also suggest getting the system scanned for codes and to observe the coolant sensor data, to see if it is reading correctly.....