So far all the advice I've gotten on here has been spot on, so figured I should ask about these codes as well.

2003 Disco II SE with just over 80K miles.
P1171 and P1174 both show up together after about 100 or so miles of highway driving. They show up faster if I reset it and then just drive around town, but takes a lot longer for them to come on doing the freeway only.

Any idea where I should start troubleshooting?

Not sure if it matters, but a couple possible related or just coincidental things before the codes came on:
1. The Transmission was destroyed by the front drive shaft failing, so I did have all 4 02 sensors unscrewed and out of the exhaust during the new transmission swap. Codes didn't come on for at least 3-400 miles after that transmission swap though.

2. I took it to Nevada on some dirt off-road type trails, nothing too serious, but lots of dust and rough road for sure. I read if could be the MAF sensor, so I took it apart and sprayed cleaner on it. Didn't seem to help at all, but then I read somewhere on one of these forums that you shouldn't clean the MAF on these so...not sure if I screwed it up somehow by spraying it?

Thanks for any suggestions.

 

I found these codes were related to the vacuum system for the SAI. Fixing my rubber hoses and the little connectors sorted it.

They came back and I found the SAI solonoid had bit the dust.

I'd start by checking the rubber hoses.

 

Any transmission fault codes stored?

Could be the MAF, but could be just a lean condition.

 

Exactly what was wrong with mine. A couple of the hoses had slipped off, cleared codes and all was well. Doing some other work they were knocked off again and used very small cable ties for hose clamps.
......

 

I worked on these codes for the better part of two months. I replaced the vacuum hoses, PVC valve, MAF and cleaned the IACV. One other thing to do is to make sure that the intake manifold is tightened down properly. One of the other posters here, Britishautoworks here and I chewed on this for quite a while. One interesting thing to note is that others have stated that it may in some cases take sometime fro the ECU to get "adjusted" to a new MAF and other components.I also adjusted both the throttle cable and cruise control cable to the exact RAVE specs

 

Definitely one of those cases where you should start cheap.

Can be a whole bunch of things that cause these. Don't start throwing expensive bits at it first.

 

I had these same codes for a while and could never find a vacuum leak.
I bit the bullet and did the o-rings on the fuel injectors and that took care of it.

TIP:: jump the fuel pump relay ON after you hook up the fuel line and fuel rails before you put the plenum on to check for leaks.

 

Fuel injector o-rings for me too. Cheap fix, bit of labor but good how-to's here.

 

O-rings did it for mw the first second time I had the issue. The first time it was an exhaust leak between the manifold and the y-pipe.

 

Definitely a vacuum leak somewhere after the MAF. A smoke test can help you find the leak. You can find out how to do a smoke test using a cigar by doing a quick forum search or a lot of shops will have "professional" smoke test machines that can apply more pressure in the system to better reveal leaks. A friend chased these two codes for a couple years and never found the source. I now expect the problem with his truck was the injector O-rings. But he sold the truck before we tried replacing them.