it's a horrible horrible idea to goto 1U on a sunday.
The jam is nerve-wrecking, and the worst is attempting to find parking.
Tho not as bad as midvalley, it will take a decent amount of skill and patience to park your car. I suggest driving a smaller car if you have one.

From serdang, past the puchong toll and stay on the right lane and just drive aaaaaalll the way straight.
You'll be on the LDP. Just follow the "Damansara" signboards and you're pretty much safe.

You'll pass KDU college, and then go under a short tunnel. After that, stay on your left, but don't turn left till you see 1U in the distance.