Have no clue what is wrong!

You may have a vacuum leak somewhere. You can use either a rubber hose of can of starting fluid to chase down the leak.

When using a hose, put one end to your ear, the other around the intake, throttle and hoses until you find the leak. If using a can of starting fluid, make sure the engine is cold, keep a fire extinguisher close by and spray it very sparingly. If you hear the idle go up after spraying a spot, there's your leak.

Also, check Fuel pressure regulator for a leaking diaphragm. It's attached to the fuel rail and has a rubber hose attached. Pull hose and smell/feel for fuel. If there's any, replace it.

Finally, have the computer scanned for codes.

I agree, most probable cause may be a vacuum leak, I prefer the listening tube to locate any leaks, as the spry method can be dangerous, get the scan done as well, also just make sure all electrical plugs are re fitted, and anything you disturbed is as it should be.

Mark (mhpautos)