Gone thru this with my xk8 and resolved issues ( maf Cleaned and leaks fixed)
Now looking at my X-Type
STFT 1&2 are going negative 8 to 10 at Idle while LTFT 1&2 are running +15 and +18,
at road speed say 2k to 2.5K rpm STFT go to Zero while LTFT drops to 4 .0 to 6.0.
I've gone over engine looking for leaks, found none, removed and cleaned MAF sensor, am I missing something? Is this ok for a 2.5L X-Type? seems high to me at idle, my other jag never reacted like this and as described above, issues resolved easily.
Any feedback welcome, oh and car runs great, haven't yet taken on along road trip, but probably will this summer.
Cheers
Jeremy

 

It's easier to get the engine hot then park.

Watch trims at idle. STFTs should be small. Ideally LTFTs also small.
(If the STFTs are not small then the car is probably learning and you should know why / what you've done really.)

Then rev to about 2500 and look again.

If the idle LTFTs were above (say) 5 or 10 and drop on revving you can be almost certain you've an air (vacuum) leak.

Other odd behaviours but not the above can be such as faulty/dirty MAF, clogged cat(s), inadequate fuel flow, an exhaust leak, etc.

NOTE: you cannot normally hear air leaks that will ruin the trims (because most leaks are small). Any hiss is a HUGE (to the car) leak.

When hunting for leaks you have to think of every vacuum hose / vacuum path. Some you can check fairly easily either by a smoke test/machine or by carefully spraying something near each suspected hose/joint while watching the STFTs closely. STFTs go mad if you spray at a leak. (You can spray something that won't burn or something that will burn. I quite like the latter but be sparing!)

(Looking at road trims is OK after the above but can be very confusing. You do sound to have a leak but try the above to check.)

 

+1
Anything above 5% at idle would indicate an issue, should be below.
How many miles on the vehicle? When was last time fuel filter has been changed, spark plugs, etc...?


IMT valve O-rings are common issue. Check all the vacuum pipes as they are plastic, specially the one from intake manifold to brake booster.


Another thing you can do when checking fuel trims while at idle, is spray some brake cleaner around the intake manifold, throttle body, IMT valves area, etc... and see if the fuel trims start fluctuating. If they do, then you've got a leak somewhere, this will be easiest way to locate. If they don't fluctuate, then its possible you have a faulty MAF sensor, have seen this sensor cause havoc on the V8's, but wont be limited to them.

 

Guys
Thanks for the input, auto has 81k on it unable to verify service history but starts well idles smoothly, will investigate further for vacuum leaks.

 

Just replaced fuel pump and filter for this and corrected it. Mine got to the point where it would stall. But poor gas milage and fuel trim is a sign.