Just got the Rover back with a replaced engine after the cylinder drop (up or down so as not to create a debate). I am still running the same codes as I was before replacing the engine which are P1172 & P1175. After some investigating they could come from a vacuum leak, a bad MAF sensor, or a dirty air cleaner. My air box lid has several missing clips or plastic is cracked (one is on order) but I am going to assume that this would not throw these codes because they are on the box side of the sensor. Other than some vacuum leak on the air intake ducting on the engine side of the MAF sensor is there anything else I can check or do that could be throwing these codes?

 

Can anyone give me trouble shooting steps for these codes. I really have researched the post on the forums but it is confusing. Specifically my questions are:

1) Running just P1172 & P1175 without any other codes is the most likely issue a vacuum leak on the engine side of the MAF.

2) Can broken plastic on the air box lid around clips (causing a vacuum leaks) trigger these codes? I would think since the leaks are before the MAF that is unlikely but really I dont have a clue!

3) Without any other codes and ruling out vacuum leaks is replacing the MAF next step

4) Without any other codes and ruling out vacuum leaks and MAF could oxygen sensors be the next likely culprit

 

Replace the filter box, Paul Grant is a good one to call for a good used one.
Those 2 codes are not enough to warrant a new MAF, not yet anyway, usually if you have a tranny code like a 733 or 734 and or a 100 to a 105 fault code, then you would replace the MAF.
Start with the filter box.

 

Most likely you have a vacuum leak. A vacuum leak or MAF or the only logical reason you would be getting a lean code. Check everything vacuum related. I have had first hand experience in diagnosing this code and have found items such as leaking fuel injector o-rings to leaking brake booster cause it. Never heard of the air box causing a leak. The engine IS GETTING unmetered air!

 

Don't get the codes confused.

P0172 & P0175 are RICH codes, bank 1 & 2 respectively.

P0171 & P0174 are Lean codes.

An air filter box issue could cause a code like this, in the sense that if the air is disrupted as it flows across the MAF sensor element, it can cause a misreading. I have seen incorrect air filters in BMW's cause lean codes.

A bad MAF could also cause that. If it reports there is more air flowing into the engine than there really is, it will spray too much fuel.

Other causes of rich codes could be dripping injectors, high fuel pressure, incorrect coolant or air temp sensors.

 

I replaced the airbox lid with a new one and put in a new filter. It definitely seemed to help, but it is still giving P1172 & P1175 just much less frequently. After clearing codes, it will go several days without showing them again. I have an ultra gauge so I know when the codes are triggered. It seems they trigger when it has been driven for a while and then I come to a stop with the engine at idle. Not sure what the next trouble shooting step is?

PS. I was running the codes before the new engine (newer used), so I am assuming they are not being driven from something engine related.

 

From the Bosch ECU manual -

So that is why it shows up after two drives. Unmetered air is a frequent culprit.

Imagine a bowling ball on your garage floor. Place a 4X4 foot square of plywood on top of it. Now climb on the plywood and maintain your balance. This is what the ECU is doing by juggling all the sensor inputs. And it is running into the program limits, about 23% change is the limit for the fra value (multiplicative correction). Airflow is one of the prime ingredients, and a clean MAF with a solid vac hose system is good to have.

Some have restricted the air hose with a clean oil filter to make a vac leak really scream.

Section attached from Bosch manual.

 

I tried to understand that ........ Not sure I did though. Bottom line question though is there anything I can try at this point? I have been told that replacing the MAF does not make sense with only these 2 codes.

 

Well, air leak past the MAF is a possibility (hose cracks, leaking gasket (such as intake manifold or even valley pan). You can also reset the codes. Unplug the MAF. Drive truck. It won't run well, and will use a backup value based on throttle position. Will make codes, but perhaps not those you have been fighting.

You could also clean the MAF, when cold, key not put in ignition since night before. Use a made for MAF spray.

A vac leak could be valley pan gasket, intake manifold gasket, o-ring around a fuel injector, anywhere past the MAF where a vacuum leak can allow in extra air not accounted for by the MAF. Some spray small quantities of carb cleaner on suspect areas looking for a change in idle.

Since you used the term "got the Rover back" - would there be a paid mechanic involved and wouldn't this be warranty? It is pretty common to have manipulated the upper intake gasket, etc.