[EDIT] I drive a 2003 Disco SE

So over the past year I've had the lifters replaced, the cylinders plug welded, rebuilt my driveshaft, calipers replaced, cooling system replaced, bought a new set of tires, sealed the sunroof, all new window regulators, and countless other small things.

Until it's about as best as it can be, I've got two check engines that return every 5 days or so:

P1171
P1174

It looks like I've gotta replace the MAF sensor judging by the forum searches. Then again, I'm not sure. In addition, my truck used to rev to around 2000RPM on a cold start until I cleaned the throttle body fully and dry lubed the moving parts slightly. It revs fine now (slightly above 1200) on start before dropping but every once in awhile I pull those check engines. I clear them, they're gone for 5 days or so then come back.

What's the plan?

 

Throw up what those codes mean (a quick google will tell you). Most guys won't go searching for you and you'll get more responses if you do that little bit of leg work yourself.

 

Maf or vacuum leak

 

Make sure you don't have a unmetered leak. A unmetered leak in a leak that lets air in after the MAF. This will cause a lean condition. Mine was caused by the hose to TB connection not clamped tight enough (I had to tighten it with a socket vs. flathead). Others have had fuel injector o-rings leak. You can do a smoke test to find leaks.

 

There are lots and lots of places to leak. There are a lot of very brittle (by now) hard plastic vacuum line.

 

It doesn't list anywhere what the codes mean, only what it could point towards which I've listed

 

P1171---- System too lean (bank 1) ----Additive injector adaptive fuelling - lean limit exceeded LH bank

P1174 is the same for bank 2.

Forget about the MAF. This is more than likely a leak within the intake system, after the MAF. You need to systematically check all the joints in the intake side, making sure they all secure. Don't forget the upper and lower intake manifold gaskets, especially if any work has been carried out which would have required the manifold to be removed.

Less likely, as a left and right lean fault is usually before the cylinders, but worth checking all-the-same is to check the exhaust side joints, as again a leak here can give the O2 sensors a false indication of the exhaust gases coming from the cylinders so check there are no leaks in the manifolds.

If all seems well in the above and everything is secure then there is one last likely cause that's over looked by many, i.e. the seals on the injectors. The seals are not expensive and it is worth changing them anyway and while you're there fitting new manifold gaskets.

 

Hmm. I'll take a look at that, thank you

 

For air leaks after the MAF, get a can of starting fluid, and spray various parts with the engine running. When the RPM goes up, you have narrowed down the source of the leak.

 

Not always a foolproof method, as many have found, but worth a go, especially around those joints and gaskets that are accessible. It will almost definitely not detect leaks around the injector seals as you cannot get at them to apply the spray.