95 Cel P1131, P1151

Whenever the windstar drops in altitude on the interstate, from about 4300 feet to about 2800 feet, the CEL light comes on. It (the CEL) goes off after returning home to the higher altitude. The codes pulled are P1131 and P1151. My first thought is cleaning the MAF sensor, if it has one.

Any other thoughts?

Whenever the windstar drops in altitude on the interstate, from about 4300 feet to about 2800 feet, the CEL light comes on. It (the CEL) goes off after returning home to the higher altitude. The codes pulled are P1131 and P1151. My first thought is cleaning the MAF sensor, if it has one.

Any other thoughts?
Are you sure its a 1151 and 1131 or is it pP0131 and P0151 The 131is up stream heated 02 sensor low voltage bank 1 and the 151 upstream heated 02 circuit low voltage bank 2. If this these are the numbers I would first have your battery checked and tested. A few weeks ago my windstar battery went low the only problem was a slow morning start but dash lights also started to act funny but after that and the alternator started picking up the load you would never guess the battery was low because it seem to run fine at least to my wife I notice the power was not there a little.. After replacing the battery the thing run like brand new.. If your battery checks out fine i would check the connections to those 02 sensor for corrosion around the connections.. hope this helps..

I was going off memory on the first post, but after checking my notes when I read the codes, I believe I had them correct. They are MFG specific P1131 and P1151, and not generic codes. It's possible, but not probable, in my opinion, that the o2 sensors could both be bad. It seems to me that a fault upstream has them registering a lean condition.

I know that your '95 has a MAF.
I have a '96, and they made some major changes in '96, but this information should help you get the point. The MAF is located in between the air filter and the flexible hose that connects to the throttle body.
I posted pictures on how to clean the MAF in my pictures at http://community.webshots.com/album/201931518cScpNK

You should not have problems between altitudes with modern computer controlled engines. In the past, it was an issue, but now they are SUPPOSED to adjust to conditions.
I would try cleaning the MAF sensor with non-residue electronic cleaner first.
I find it hard to believe that the oxygen sensors have failed on both banks at the same time. The sensors are rated for 100K miles. I replaced mine at well over 150K miles, and really did not notice any difference.

Of course general maintenance, fuel system cleaner (such as Chevron Techron), spark plugs (good for 100K miles), Air filter, fuel filter, and so on should be kept in mind.

Thanks, This is my neighbors van (my 92 Explorer isn't OBD II, so it's a little different) I'll try the MAF cleaning, suggest a tune-up, and go from there...