Need help with a 2000 Accord ASAP
 

Hi, I'm a mechanic and my friends 2000 2 door Honda Accord EX 2.3 was mixing oil and coolant, which was a head gasket. He drove it to my house, and I replaced the head gasket, water pump and timing belt which I did correctly.

Now my problem is, when the car is left running its fine but right when you press the gas it cuts off, which it didn't do before. The check engine light came on and it was a knock sensor code so I changed it and reset the light but it didn't fix the problem. Then the check engine light came back and it was the crank sensor code so I tried a new one, but the same issue with pressing the gas and cutting off, so nothing worked.

I've had the car for 2 weeks now and my buddy is mad and wants all his money back including the money for parts, and I can't figure out whats going on. It didn't do it before, and nothing is out of place either.