ever since this spring I have been chasing a P1176 code and just recently a P1178 has appeared with it. These codes , if you look them up , dont really point you at any thing specific......sort of a "hail Mary " from the ecu...." somethings wrong..we just dont know where". The codes are air fuel related( yeah, yeah I know... most of them ARE ). The ecu has made adjustments to the air/fuel ratio as far as it can go and apparently thats not far enough. The truck generally ran good, in a good state of tune.....but here were a few sporadic symptoms I had noticed.
1. starts good cold, but MIGHT stumble at start when warm almost as if it werent getting fuel enough for an instant( pump was new last winter)....idle was always good once
it was running.
2. with a warm engine....if you cleared the code and restarted the vehicle, the code would come right back. If you cleared the code and let the vehicle cool off ( all day or overnight), the code would stay away for an indefinite period of time....maybe 100 mi. maybe 1000 mi.
here's what I did over many miles... new plugs and wires / re-cleaned a clean throttle body/ induction cleaning / injector cleaner/ replace a visibly clean air filter with a new one/ recleaned a clean IAC valve/ and none of this made any difference .
I consulted with a "Land Rover Tech" who told me to replace the MAF sensor.....but try cleaning it first. I bought a used one from a reliable source.....made no difference....cleaned my orig one AND the used one ....made no difference.
Of course when I did any of these things the damn light would stay off for a while and lull me into thinking I had cured it. WRONG.
Well...one day the 1176 was back and brought 1178 with it....things are getting worse and I really hate to get beat by a machine. I went looking for a vaccumn leak and didnt find a smoking gun. Tryed the carb cleaner spray all over every thing and nothing appeared. tightened a few hose ends up, no change. WTF ?
Well nothin' to lose...I took off the intake plenum/throttle body to get at the intake manifold bolts ....you know ...the the area I just sprayed carb cleaner at.....and every bolt except one, took at least a half turn or more to bring to bring them even close to tight. long post short.....no codes and better starting when warm. Obviously when the engine was warm things would have expanded to allow just enough air to be sucked in by the gasket. which is why the code always came right back when the motor was warm.
sorry for the long story...but I hope this helps someone in the future with these troublesome, hard to diagnose codes

 

I had the same thing about a year ago. I was only getting the p1178 code. Could not find a vacuum leak anywhere, and threw parts galore at it(plugs,wires,different MAF, O2's,air filter, fuel filter,you name it)

Decided I was going to put a new intake valley pan gasket. After taking off the plenum, found the rear-most 4 or 6 manifold bolts not even finger tight.

Being that far, I replaced the gasket anyways, and no 1178 code in a year +, and 20K and some odd miles.

 

Very valuable info! Thanks!

 

Good stuff!!

luck,greg