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Thread: P0171 P0174 LTFT 24% at Idle
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10-14-2020 #1
P0171 P0174 LTFT 24% at Idle
I'm throwing P0171 and P0174 codes on my 67 Camaro with an LS2/T56. The engine is stock with a CAI and headers. The car idles and runs fine under all conditions. I checked for vacuum leaks but found nothing obvious. I was checking out the fuel trim readings and note that at idle the LTFT for both banks are at 24% (which I understand is the threshold for throwing the codes). When driving they decrease but always return to 24% at idle or on decel. The STFT seem to fluctuate depending on load normally somewhere +or - of 10%. I pulled the MAF and cleaned it but that did nothing. I did notice this afternoon that a driver side header bolt was missing, closest to the firewall. I'm going to replace it, but doubt that is the source of my problems. My limited understanding of STFT and LTFT is that the ideal number would be closest to 0% which would indicate a good AFR of 14.7:1. I understand that the STFT will bounce around depending on load, but the LTFT should be closer to 0% more consistently. I am still thinking there is a vacuum leak somewhere which is causing both banks to read 24% for LTFT at idle, just not sure where else to look. I guess making my own smoke tester would be a logical step to rule out a vacuum leak.
Any thoughts on this issue?