codes p171&174 and also p0401

was wondering could bad egr flow from code p0401 also cause codes p171&174

Possible, if there is unmetered air, instead of exhaust entering the intake manifold. However as your vehicle is a windstar I would wager it is the isolator bolt grommets. Try http://leckemby.net/windstar/windstar01.html

Totally agree about the isolator bolt grommets, but it can also be a bad DPFE sensor. If the sensor is reading low flow, the EGR valve will open up and dump too much air into the EGR. Excess air will give you the P174 and clogged/crudded EGR ports inside the manifold can give you the misfire P0401. Do a search for DPFE and you should find some explanations on how to test or PM me and I will try to help you test the sensor. I think I explained how I tested it about a month or so ago, so even if you manully search back for threads started by me in the past few months, you will find it. It is a simple test and doesn't take more than about 30 minutes for a Deathstar.

The DPFE sensor is a common failure item for FORD. Easy to change, but FORD charges an arm and a leg for one. Some people do not like aftermarket ones, but I used one without any problem so far and it $40 versus $140.

yep, it's the dpfe. Do a search and you'll find a lot on this topic. Seems that after many people do the 171/174 the 401 shows up. It's probably the easiest fix on a windstar. Make sure you get a plastic one not the aluminum one. The al one corrodes which leads to problems.

Yah I guess I should have mentioned what Northern Piper said about the P0401 right after the P0171 fix. I had the exact same thing happen to me about a month or so after fixing the grommets. BUT I still suggest you test the DPFE because then you know for sure that that is the problem instead of guessing and doing repairs by trial and error. You learn by testing and you can save $$$ too sometimes.

might possibly be isolater bolts but seen on diagnostics of codes and repair on another site that p0401 bad egr flow sensor noted for ford and will also give codes p171&174 mine already has plastic one but for $40 bucks will try this for the p171&174 codes before tear into plenum for possibly nothing

Another easy way to see if it is likely the DPFE is to remove the sensor from the van and use a light to look in the two sensor holes. If you see nothing but carbon build up in there, then it is toast. Otherwise, in mine, there was bronze coloured metal in at the bottom of the hole. In my case, it wasn't build up, it was the sensor was stuck at one voltage. If you do the voltage test by applying vacuum to the EGR valve with the sensor installed and van idling, you should be able to stall out the van, but at the same time, you should see the voltage on the sensor output wire changing. If it doesn't change (careful you checking the correct wire), then it is toast. Simple test, but you need to vacuum to the EGR valve. I had the cowel off, so it was easy to remove the egr valve line on the back of the passenger side of the engine from the solenoid and connect it to the heating system vacuum line which is also in this area. You may be able to get another vacuum line and not have to remove the cowel, but that is how I did it.