So my 99 XJ8 had a code (P1074), so I thought I’d change the MAF sensor, seeing that I knew there was a brand new one in the trunk when I bought it. The one in it was a Denso, the new one in the trunk was a Delphi.

After changing it, it ran much worse. Put the original back in, and it runs better. Any ideas?

 

I’d highly suggest taking the Denso MAF sensor and carefully clean it out with brake cleaner then blow it out with compressed air.

 

Denso is better choice, but you may have dirty connectors. Using electrical connection cleaner, spray both male and female connectors then connect, remove, reconnect, maybe a couple cycles more, to remove any oxidation (check for any bent prongs on the male side or wires pulled loose on the female), then clean the throttle plate and bore and check the air tube from the filter box to the throttle bore for leaks.

Maybe a bottle of a good fuel cleaner (I like SeaFoam) in a tank . . . and let us know

 

Use maf sensor cleaner and use the old one
unfortunately Delphi maf sensor doesn't work at all on the x308 I tried brand new out of box didn't work
Bought new denso part number 1976040

 

I’ve also had a bit of bad luck with the new Denso MAF’s. In my experience, buying used original Denso MAF’s followed by a thorough cleaning seems to be the trick.

What I completely don’t understand is in this day and age, why can’t there be any good aftermarket replacement MAF’s available? I remember 25 years ago some guys on the Turbo Buick forums were having difficulty with the aftermarket MAF’s for the GN’s. Turns out they were just garbage and buying used OEM MAF’s resolved the problem. That’s why I bought a good used OEM one for my GN back then and I still haven’t needed to replace it yet.

 

Code P1074 does not exist in Jaguar DTC Summaries so your problem may not be in the MAF. What problem with the engine are/were you actually having?

 

Sorry, my apologies, the code is P0174

 

P0174 means B-bank too lean so the issue should not be in the MAF sensor as it would affect both banks.

 

Unfortunately many new denso MAF are not made in Japan the old one Japan made the new one I bought I think it's Thailand made or Malaysia its working fine but I was surprised that's made in Thailand , denso Japan made is always better . Btw Mazda rx8 use the same MAF we have on x308

 

Apart from the code, what are the symptoms and what have you done so far apart from changing the MAF? With the Denso MAF in, it runs "better", but how well does it run? Is it fine and you just have a check engine light or is it not running right and its just less bad with this MAF than the other one?
One whole bank (left side is B if I'm not mistaken) running too lean has me thinking about all the things that might be involved in how the air/fuel mixture might be adjusted on only one side of the engine. Vacuum leak, O2 sensors, clogged injector(s), coil or plug issue (which I would think would lead to too rich if anything, but maybe?), cam cover gasket leak, part load breather tube from the cam cover to the air intake maybe isn't sealed properly or it has a leak and is drawing vacuum in instead of oily air out? Clogged cat on that side maybe?

 

So the issue I'm having is that I am getting random surging while accelerating. My next step that I am going to take is to remove the air intake to the throttle body and give it a thorough cleaning, and while I have it apart, I am going to run a smoke test to look for leaks in the vaccum system. If anyone has any other suggestions, please advise.

 

Surging could well be a crack which opens & closes causing an air leak at times.

 

Check this too
https://www.jaguarforums.com/forum/x...solved-105386/

 

I vividly remember this era of Turbo Regals/Grand Nationals parts availability! Used OEMs that were well cleaned always worked. There was a period too that the coil packs were all crap as well... I miss my turbo Buicks, I keep thinking about getting another one. Those forums used to be so active, I don't even know if they're still online (turbobuick.com, turbobuicks.com, gnttype.org I think...)

 

I will definitely look at the O2 sensors after reading that post forwarded by SilverJag. I'll keep everyone posted on my progress

 

If you have weak motor mounts and if you got on it a little bit, maybe it’s enough to either temporarily separate the intake air pipe at the TB or at the air filter lid or you have a small crack in the bellows that you haven’t noticed yet. A smoke test can help but it’s time consuming.

57, I’ve had my 86’ since 98’ and it’s always on the back burner but, it’s my forever car. I’m not driving it but, it’s in the garage, not getting wrecked or stolen. It will be worked on soon though. I just need to clean the MSD 50’s in a sonic cleaner after I take them off the car. I took it off the road because all the control arm bushings have disintegrated and was unsafe to drive.

 

So today while I was out and about, I decided to get some Techron at the auto parts store, seeing that this would be my first fill up since I bought it. I poured it into the tank, screwed the cap on, got in, and the check engine light went away, and now it is running as smooth as can be. Question is, could a loose gas cap cause P0174?

 

So need to take my prior statement back. It WAS running perfectly for a little while, then started doing it again.

 

You have really dirty fuel injectors.

 

I'm not sure if you know how to pull the intake manifold and clean each injector by carb or throttle body cleaner
Injector seals and intake gasket not expensive replace the fuel filter too remove the rear left tire to have access prefer to change it when the fuel is very low to avoid dripping while changing it's really mess if you replace fuel filter with full tank . I hope you have another car because it looks like you will need to park it for time