I have been reading up on the above codes but need some additional info.
The above codes only show up and the CEL turns 'on' if I goose the throttle to take off from a stop.
If I clear the codes and drive like a gentleman, nice and easy the codes do not show up.
I may have a slight vacuum leak from the hose that go to the bottom of the throttle body from the left hand side valve cover (PCV?) which I will address this coming week to be sure.
I know I have to eliminate any air leaks, fuel system (maybe the fuel filter) and other items that may cause the codes.
I have seen this as a common problem on the XK8s so I will be looking at any item which may cause the codes
IDEAS?????

 

Maybe start with a smoke test and fuel pressure test ?

Since you have both P0172 and P0174 it seems like a problem common to both engine banks (e.g. air leak between MAF and throttle body, Low fuel pressure or bad MAF).

A smoke and fuel pressure test will highlight the obvious problems.

 

I was thinking along the same lines. I believe the NORMA connection at the bottom of the TB may be the culprit. i had reused the TB gasket so I will purchase a new one.
When I first started the engine after doing an overhaul I had cleaned the MAP sensor with MAP sensor cleaner. I am leaning towards a vacuum leak somewhere.
I have a smoke machine and a fuel pressure gauge so I am good with that.
My car has the correct new sparkplugs and 8 new coils. Not so sure about how good the injector oring seals on the bottom are. I think that the injectors are working fine because I got the car up to 100 MPH without a struggle,or misfire but who knows. Will start working on this issue on Monday. The suspension rebuild has me pretty much tired.Taking a couple of days off to recuperate. Too old for this s**t lol.

 

Another potential air leak source are the two VVT solenoid O-rings. If they are weeping oil, they are also allowing air to pass through....

 

@Jon89 When I overhauled the engine I replaced every single gasket and oring. So I know they are new and seated properly. then of course you never know
BTW: where is the best place to attach the smoke machine to do the smoke test? Anyone?

 

It depends what fittings you have but the best place from experience is to disconnect the intake pipe from the air filter box and connect there.

 

Hell-Cat. Thanks.

 

I'm probably missing something here, but aren't P0172 and P0174 rich on one bank and lean on the other? Are those the right codes?

 

I had the same problem. I did smoke tests and replaced the throttle body gasket and still had problem. Scanner showed MAF was working prorperly - that is it was giving correct readings. Turns out that replacing the MAF sensor solved the problems. I was told by experienced mechanic that sometimes MAF shows good but it is actually bad. That was problem in my case.

 

Please check - as asked above - really both P0172 & P0174?