My 05 TL Sport 6MT with 140k miles runs great, but I use my phone with an OBD II dongle for monitoring, primarily of fuel trims, vacuum, and coolant temp (I've had quite a few tuned/project cars and just like to know what's going on, even though this car is bone stock and really doesn't need that level of monitoring). I've noticed lately that fuel trims were about 11% (combined short term and long term) on B1 and about 9% on B2, so very close, but a bit on the lean side for my liking. Also, when under steady-state cruise at light throttle, short term fuel trims would occasionally climb rapidly up to 25% (the max my gauge shows) and stay there until I let off the gas. When I get back on the gas, the fuel trims go back to high-normal. The car may have been like this since I've owned it (bought about a year ago and put about 10k miles on it), didn't monitor right away.

Also, long term fuel trim on the higher cylinder seems to fluctuate between about 4-6%, with short term fuel trim being about the same, but fluctuating rapidly. Interestingly, when short term fuel trim goes below long term fuel trim, long term seems to reduce, albeit slowly, despite short term trims never going visibly negative on my scan tool, which is not how my previous vehicles behaved (on previous vehicles, STFT would have to go negative for LTFT to begin to reduce). Research on these forums, however, indicates that the 3G TL total fuel trim is STFT + LTFT, so not sure there...

At first, I cleaned my EGR valve, cleaned under the intake manifold top plate (i.e. the EGR passages), cleaned the throttle body, inspected the air filter, cleaned the factory MAP sensor, changed the MAP sensor to a new, OEM one, smoke tested the intake and EVAP systems, vacuum tested the motor mounts, plugged the EVAP and brake booster systems for testing, and unplugged the EGR valve for testing, without any noticeable change in drivability or in fuel trims.

I then replaced both primary O2 sensors. This did seem to reduce fuel trims a bit, but LTFT is still about 3-5% positive while STFT is another 4-8% on top, which still seems high to me. The intermittent maxing out of fuel trims, however, appears to be gone.

My next step is to pull the intake manifold and replace it with a J35A6 manifold (the magnesium one that splits in two) so that I can clean the inside of the manifold well and then swap it, my thought being that EGR flow might be low, causing the high fuel trims. If that doesn't work, I may send the injectors off for cleaning/flow and pattern testing.

Anyone have any ideas?

Also, I have the factory service manual for this vehicle and it states that high radiator fan speed is called for anytime the temp exceeds 206F. When watching my scan tool, however, I see temps of about 180F cruising that go up to 208F before the low speed radiator fans kick on; this brings temps down to about 195F within a minute or so and high fan speeds are not needed in any conditions I ever encounter. I can monitor ECU demand for fan speed and confirm the ECU is only calling for low speed operation at exactly 208F and have also tested all relays, wiring, and the fans themselves and there is no apparent issue, but this apparent discrepancy is odd to me and if anybody has an explanation I'd be interested in hearing it!

Thanks for reading!

 

have you checked the injectors to make sure they are spraying properly? Also, are you using gas from the same station or a different ones?

 

Thanks for taking the time to respond! I have not pulled the injectors yet or otherwise tested them. I do have an injector block that holds an injector and allows you to spray an aerosol through it while energizing it to clean it out, but is there a better/easier way you are aware of? I typically just send them out for testing and cleaning to a guy not far from me who has a flow tester and takes before/after measurements as well as photos of the spray patterns, again both before and after; he charges about $100 for 6 injectors and includes new seals. I will do this at the same time as cleaning/replacing the manifold/EGR passages, but am leaving this for last because the car will be down for a week while I'm waiting for the injectors and, while I do have a backup vehicle, I like driving my TL!

Regarding fuel, I typically fill up at Sunoco with 93 Octane (10% ethanol). I did run a can of B12 chemtool through the vehicle last fillup (still have about a 1/4 tank). I believe I have filled up at a Shell station without apparent change, but will make sure to fill up at a different station next time and pay more attention to confirm.