To simulate HTTP request delay:
tick on menu: Rules -> Performances -> Simulate Modem Speed
To change the simulation details:
click menu: Rules -> Custom rules
// Delay sends by 300ms per KB uploaded.
oSession["request-trickle-delay"] = "300";
Links:
http://www.fiddlertool.com/fiddler/Dev/ScriptSamples.asp
http://www.chencheng.org/blog/2009/12/31/fiddler-problem/
Other tools:
Speed Simulator
speedsim
Network Delay Simulator
net limiter