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I have an interesting situation with fuel trims and would like any input and advise to help me and everyone else with high fuel trims at idle when the engine is hot.
Over the last year I have been improving my fuel trims a little at a time by doing some work.
Replaced all vacuum lines, plenum and lower intake manifold gaskets, valve cover gaskets, gas cap, oil cap, pcv, etc, etc, etc- no vacuum leaks detected anywhere.
Also, replaced A/F sensors and MAF too.
Here is my fuel trims and MAF data after warm up at idle.
But- here is where it gets interesting-
As the car continues to heat up after being driven a while for 30 mins or more and the engine is good and heat soaked the fuel trims creep up(only when idling).
* Notice the air intake temp is much hotter(134 F) when the fuel trims rise to +14 combined.
When driving the fuel trims hover around +5 combined for LT and ST- it's only higher when idling.
All the videos and posts I have seen says it must be a vacuum leak or a bad MAF, etc when the fuel trims go over +10 but I took it to a mechanic today for a 2nd opinion to have diagnostic scan and vacuum testing done and he said it was normal and typical for these cars to run lean at idle and found nothing wrong.
I would like to hear other's experience with fuel trims and any experience you have on this to add.
Thank You All.
Last edited by Margate330; Dec 11, 2019 at 10:35 PM.
I don't really see anything out of the ordinary here. The only thing I can really suggest is perhaps try to fabricate some sort of air scoop for your intake to get more fresh air directly from the bumper or try to manage underhood temperatures and reduce engine bay heatsoak by venting your hood or something (maybe if you live in a hot area)
If you see 134F intake temperatures while idling and it's cold outside, that would cause me to be a bit concerned.
I found a link which you may find useful, if you want to do some more digging around with your fuel trims and whatnot:
I don't really see anything out of the ordinary here. The only thing I can really suggest is perhaps try to fabricate some sort of air scoop for your intake to get more fresh air directly from the bumper or try to manage underhood temperatures and reduce engine bay heatsoak by venting your hood or something (maybe if you live in a hot area)
If you see 134F intake temperatures while idling and it's cold outside, that would cause me to be a bit concerned.
I found a link which you may find useful, if you want to do some more digging around with your fuel trims and whatnot:
Higher Fuel Trims When Engine Hot
