Rep Power: 0

I apologize if this has been posted before in another thread, but as I am unsure of the root cause, I didn't know how to search. I have an 02 LX. I currently have a K&N short ram and a header as the only engine mods. Here's the issue: A few nights ago I drove home from work. Car ran fine. Picked up my daughter and left car running while I did so (approx 10 minutes). Pulled off fine but then engine started running rough. Idle dropped and car shut off. Cranked right back up but would not get above 1500 rpms. Car would only go 35mph tops. I nursed it home (5 miles) and parked it. Noticed an antifreeze smell and noticed antifreeze on top of radiator where top piece meets cooling fins along the length of the radiator. Temperature normal runs at halfway on Guage and only climbed to 3/4 on Guage bf lowering back to half. That was Wednesday night. Today I went to check plugs and cranked it up just on a hunch. It ran and revved fine. I didn't bring it up to temp bc of the fear of there being the radiator leak. Any info on this would be appreciated.
Thanks

 
Rep Power: 519

Refill the radiator with antifreeze.
Check for leakage.
Check oil level.

Check fault codes.

Test for blown head gasket.
Test radiator fans operation.

 
Rep Power: 257

clean out your throttle body and intake idle control valve.