please do not ruin your engine by actually driving it with ATF. It has high detergents, but the flash point is a lot lower than oil so it burns more easily. This can ruin the cat yada yada.
Only run the engine at idle. If you want to get rid of sludge, just run a nice synthetic. My wife's car was all sludge when I bought it but now she has a nice tan, and no sludge. All I have done is switched to mobil extended performance.
Pennzoil was reformulated beginning of 2008 and I am pretty sure the synth has even more detergents than mobil. The new castrol Edge is what I will be running next.
I drove my pos festiva with ATF in it and it burn that stuff like crazy. Looked like an engine fire constantly hahaha. But the good thing is, I got free car washes. Firetrucks would just pull up and start spraying her down for me