Engine running rough

We have a 2001 Windstar, about 8 months ago we had the P0171/P0174 fix done. Lately the engine seems to be running rough. A few days ago we turned the heat on after driving about 40 miles and only cold air came out. After turning on the rear heat the front heat kicked in and has been fine ever since. It sounds like a low constant air sound even with the blower shut off. Any ideas?

sounds like a big vacuum leak.

Any idea where we would start to look to figure out where?

Pinch off the hose to the vacuum brake booster. If it runs a lot better replace. Get a can of carburator cleaner and spray around the intake manifold.
If you hit a big vacuum leak the engine will smooth out. Spray around the base of the injectors. Pull the vacuum hose from the fuel pressure regulator. If it has gas in it replace.

If there is a leak shouldn't the CEL come on? It also seems to lose a lot of power when defroster or a/c is on.

If there is a leak shouldn't the CEL come on? It also seems to lose a lot of power when defroster or a/c is on.
no not always.. I think there are 4 connects to the manifold plenum area. I take a look at those 2 small hose One larger and maybe another back along there although it will be eaiser to find if the cowel is off.. But it sounds like you have a vac line loose somewere. It will loose power if you add the ac too the loop because it is already running rough. I think the 2 small thin line that connect to a check valve that goes to the intake plennum may be the problem. if one came loose.

So the problem is the hoses/lines not the intake itself? How hard is it to change them? We tried different things tonight after work but couldn't pin point exactly where it coming from.