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Discussion Starter · #1 ·
I keep seeing around +5 LTFTs at idle and pegged at +16 when you drive the car around. I know this sounds like a vacuum leak but nothing I am checking tells me there is any vacuum problem. I am seeing map readings of 16 at idle and IAC readings around 40 at idle, and I can't find any vacuum leaks.

It also has some weird + LTFT spikes at idle like in this log here:


TPS LFT1 RPM O2B1S1 MAFF
0 5 993 538 2971
0 5 1023 121 2972
0 5 998 473 2986
0 5 1050 108 2981
0 5 1030 191 2981
0 5 1015 590 2968
0 5 1014 226 2979
0 5 989 776 2956
0 5 998 429 2968
0 5 1022 789 2968
0 5 1015 802 2966
0 5 1012 815 2977
0 5 991 603 2961
0 5 1015 104 2968
0 5 1060 95 2947
0 5 805 546 2998
0 5 890 798 3001
0 10 980 69 2973
0 11 883 876 2908
0 10 853 759 2924
0 9 882 213 2910
0 9 931 416 2923
0 9 836 885 2898
0 9 897 256 2938

Any ideas? Bad o2 sensor or bad maf sensor?

My mods in case that helps diagnose: Intense stage 1 pcm, VS cam, 3.0 pulley, togs
 

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Discussion Starter · #3 ·
I'm not sure if I understand your question. No I don't have a LS1 maf. Are you saying that would help/fix the problem?
 

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Discussion Starter · #5 ·
I just got a mini afc 2.0. I can get the idle fuel trims adjusted very close to zero with it, but the cruise trims are still uncooperative. I set 5k-13k to 104% on the mini afc and still saw +16 fuel trims. Then I set 5k-13k to 108% and still get +16 fuel trims.

I'm not sure how much farther its safe to adjust the afc, and the lack of change in fuel trims makes me think its a bigger problem than lack of a good tune.
 

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IAC readings around 40 at idle
That is a vaccum leak. Low IAC counts usually indicate a vaccum leak
 

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Merc said:
That is a vaccum leak. Low IAC counts usually indicate a vaccum leak
Is that low?? What should it be at?
 

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I had the same problem. Put in a different TB, LTFT's were pegged at +16 at cruise, put the stocker back in and all was well. Turned out to be a vac leak around the gasket, my IAC count was also 40. Once the car is warmed up, the IAC should be 45 and above I believe.
 

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I do not believe it is a vacuum leak. 40 IAC counts and +5 are not indicative of a vacuum leak at all. You can double check by spraying brake cleaner around all of the joints of the intake system (TB to blower, blower to lower intake, lower intake to heads, etc) and all of your different vacuum hoses and hose connections. If the car wants to die when you spray it on a certain part, try drowning that area, and if the car continues to stumble, you have a vacuum leak.

Honestly, I don't believe you do. I think it sounds like some fine tuning is necessary on your setup.

What do your LTFT's do when you give gas aggressively and/or go wide open throttle?
 

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I do not believe it is a vacuum leak. 40 IAC counts and +5 are not indicative of a vacuum leak at all.
I have always heard that. If its not true then my bad. I do think that is very low though and should be reading alot higher.
 

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Discussion Starter · #12 ·
Problem solved: I reset the pcm and now it has +2 fuel trims at idle, and +5 trims at cruise.

I'm not sure what caused the computer to be so stubborn, but before I reset it no amount of tuning with the mini afc was getting the cruise fuel trims below +16.
 

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I'm also having LTFT issues except mine are rich (-15.x). What sensors does the computer use to determine fuel trims?
My IAC at idle warm is in the 50-55 range, my MAFF approaches 11,000 (+10,700) at the top of each gear and is around 2500 at idle, my O2 reads 960-930 while at WOT. All those seem pretty normal to me. What am I missing that is throwing my fuel trims out of whack?
 

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Discussion Starter · #15 ·
Actually I don't think you have a problem. The fuel trims can go down to -20 something before its maxxed that way. The problem I was seeing is +16 is the max amount the pcm can adjust.

As long as you are inside the range of the pcms adjustment it should be ok.
 

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I have the same problem with my car, but suspect it to be from my IC core. Ive been have a hell of a time trying to narrow it down but it runs very lean at idle. Its impossible to tune with this problem, im interested to see how you fix it, cause Im just about out of ideas.
 

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If it already hasn't been said...It has something to do with your EGR. It is OK at WOT, but at normal driving it's messed up? You may have a crack in your EGR tube from the header to the EGR. The EGR won't open as you look for vac leaks in the driveway.
 

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What about at Idle, it goes from +10.2 to -16.4 and then back to +16.4 all at idle? Within 5 or so minutes of sitting there.

The LTFT's are fine cruising. just about 0%.

Now, WOT, it goes to +16.4 every time.

O2's are around 930ish. Zero knock, and it runs great.

It's an L36 too. I've tried doing all kinds of stuff to the afc 2.0 and it doesn't seem to change anything.
 
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