I'm hoping someone can give me some much needed advice on my 5.7 silverado. The problem started about 8 months ago and has progressively gotten worse. Ok, so I can be driving down the road about 30 mph and let off the pedal and it seems as the engine stays at a high idle and will continue down a flat road at 20-30 mph, but stay with me cause it gets better. Sometimes when I go to crank it, I will have to turn it over 7-10 times before it will fire off. I can also be driving down the road and the valves will start rattling, the rpm falls immediately to 0 and the engine will die, but if I act quickly enough and press the gas pedal to the floor it will sometimes come back alive. It had an O2 sensor code, I replaced them to no avail. It also has a PO452 code, I don't know about that one. I am at a complete loss, anyone's help will be greatly appreciated. Thanks.

 

P0452 is Evaporative Emission Control System Pressure Sensor

Seems like a leak but dont have experience with EVAP system to tell you were to look.

If you have zero experience then take it to a trusted mechanic or start searching online with your code.

 

If you have to crank it 7-10 time to get it to start it might be a fuel issue.I would pressure test the line and see what psi you get and rule it out if you receive a good reading.Also i would change the fuel filter since they are cheap and easy to change.
I myself like to start with the easy or cheap fixes before going after the expensive ones.

 

The PO452 is a Fuel Tank Pressure Sensor Circuit Low Voltage
Here is a page i found-
P0452 GMC Fuel Tank Pressure Sensor Circuit Low Voltage OBDII Engine Light Trouble Code | Engine-Codes.com