KA throwing code 21 and not idling

[Kakid240]

well i blew my headgasket and put on a new one so i put the car back together. The car starts but it wont idle it just shuts of when i start it. I checked the codes on the ecu and code 21 is coming up i cam confuse because the car starts that means it is getting the voltage it needs??? i am puzzled on why my car just shuts of when i turn it on and why it has code 21 if the car starts PLEASE some one help me

[Kakid240]

i checked codes again and it is throwing 55 which means nothing wrong but my car still wont idle so i turned the car on and held the gas at WOT the car like had to wait a while to catch itself and then it stumbled and went to about 3500 rpm and then shut itself off!!! wtf could it be

[rioredstang]

Can you keep it running or will it just die? Could be a fuel pump problem. Maybe shutting off relay after starting. Check fuel pump relay. I think a 21 was no ign signal. Make sure no leaks to MAF. Check timing.