2000 x308 XJ8 AJ27 w/130k miles. no vacuum leaks, cleaned and flowed fuel injectors, new fuel pump, new pressure regulator, fuel pressure is ~40PSI and responds to throttle and instantly recovers, 5 gallons of gas in the tank, fresh gapped plugs, no misfires, no codes, smoke checked, map gas checked for all intake leaks (all vacuum hoses replaced with my rubber hose conversions), idle between 630-680 RPM, The TPS was "rebuilt" several years back by ACI when I was troubleshooting the same problem on my 01 XJ8 (which ended up being pitted valves with lousy compression and leak rate showing it, and also a defective ECM), connectors all cleaned and not corroded, and gold pins.

Compression PSI (oiled cylinders) : Bank 1(a): 1 - 118 ; 2 - 115; 3 - 118; 4 - 116; Bank 2 (b): 1 - 118; 2 - 120; 3 - 121; 4 - 122 Delta 7 PSI. (Horrible Freight compression gauge)

Symptom: Real time ST trims are oscillating between 7% average negative and 12% positive, bank 1 & 2 very similar, and the idle is showing it. I am trying to diagnose either an oscillating throttle signal that is causing an oscillating ST trim signal. The symptom is also shown on moderate acceleration under load driving. I will be doing a graph of the commanded throttle / TPS position against the ST trims

So the Fuel Trims Primer document is great, but, what should the ST fuel trims look like when idling grabbing the values in real time? Should they be rock steady or, should they be bouncing as much as +/- 10%. I am going to guess their variation is

Also in IDS 125 for live view, my sensor list has three pairs of LT trims and two sets of ST trims, two engine speeds, a couple of MAF selections. One set of LT Trims seems to have only one bank reading over time to the ST trims and responding and the other two sets have the LT reading max 100% negative. I select the ones that seem to actually be reading changing values.

I am also playing with a couple of different ECMs, flashing them with the latest campaign V9EZ I have for v125, running throttle characterization success. etc.

Feedback?

 

The LTFT’s are way more important than the STFT’s. +/- 10% for LTFT is going to be your target albeit, closer to 0% is always best.

 

Fuel Trims, depending on which LTFT I am looking at, meaning the ones that appear to work are right at zero with LTFT 1 sometimes being +0.78%. When I was seemingly successful once reading LTFT 2 it was zero, once blipped a tad positive but back to zero.
I'd like to learn why there are multiples of STFT1/2 anf LTFT1/2, (amongst other parameter duplicates) and how to recognize which to select to see actual live data. Part of the answer is why there are updates to IDS/SDD.

Update, I changed to a different ECM, flashed to V9EZ , throttle characterization and security sync and voila, acceleration surge seemingly gone. Hoping to see P1111 and a clean emissions test.