TBSS Intake and 87mm TB swap w/ X-link, having reduced engine power and P0120...

[cabech984]

Over the weekend, I replaced the factory intake and 78mm tb on my cammed 2006 Silverado L59 5.3L with a tbss intake, 87mm gold blade throttle body with an X-Link, and a Volant CAI. I've been dealing with a "reduced engine power" message with a P0120 Throttle/Pedal Position Sensor 'A' Circuit code.

I adjusted the VE and MAF tables after swapping everything. Truck had been running great all day with no issue, but this happened later in the afternoon/early evening and can't get it to go away! I'm able to footbrake it at stops to keep the idle above where it wants to throw the code and reduce engine power.

After doing some reading online, I discovered that I should've adjusted the ETC Area Scalar setting in the Engine/Idle/Airflow settings. The factory .0208 was then changed to .0168 which was found on here on a spreadsheet with different numbers for different sized tb's. Then, I adjusted my Base Running Airflow using the RussK method that I also found on here. No change, still get the trouble lights. I did notice that my TB after warming up is all the way down to 2-3%. At cold start, it was up in the 15-16% range and no DTC was thrown until the TPS is lower. I'm guessing my IAC is out of range still. Can anyone kick me in the right direction?

[cabech984]

I got rid of the wall of text I posted last night. Hopefully someone can kick me in the right direction with this!

[cabech984]

updated the original post with the current tune and a log file of the drive I just took. It went into reduced engine power numerous times while stopped during this log. I noticed throughout the log, my LTFT's were -12.5% while cruising. At idle, it'd drop to less than one percent. My VE table is dialed in to +- 2%, especially in the cruising rpm's. Its been hard to dial in closer to idle due to the reduced engine power code, but it was currently trying to add 3% fuel on the last VE tuning log that I ran.

I'm going to go back and look at my MAF adjustments. Also set my Base Running airflow back to what it was before the intake/tb swap

[Chewy72ss]

May be a stupid question, but have you gone over all your wiring between pedal/tac/tb? A "circuit" code usually points to a hardware issue, in my experience.

[cabech984]

May be a stupid question, but have you gone over all your wiring between pedal/tac/tb? A "circuit" code usually points to a hardware issue, in my experience.

The truck was running perfectly before the intake/tb/x-link swap. I've checked the connections and all appears to be intact and clean/free of corrosion. I didn't do any voltage checks for that reason, and it runs great at any speed/rpm over idle speed. I think it may need an idle relearn, but am looking up how to do that without a diagnostic scanner. my HPTuners doesn't have that ability it seems

[blindsquirrel]

Conditions for Setting the DTC
• The TP sensor 1 voltage is less than 0.38 volts or more than 4.5 volts for more than 0.1 second.
OR
• The TP sensor 1 minimum throttle blade position is less than 0.38 volts or more than 0.71 volts for less than 1 second.
OR
• The 5-volt reference circuit of the TP sensor 1 is shorted to ground for more than 0.01 second.
OR
• The 5-volt reference circuit of the TP sensor 1 is less than 4.54 volts or more than 5.21 volts for more than 1 second.

[cabech984]

Conditions for Setting the DTC

Thanks for that @blindsquirrel. I'll take a look at the voltages and see what I find.

I for some reason just remembered that the previous owner of the engine I pulled this TB from, was complaining of a reduced engine power light and limp mode. I'm wondering if the throttle body isn't junk to begin with. The thing looked super clean compared to the 200k mile LY6 I bought with it. Wondering if an Idle Relearn will fix it, or a new TB altogether

[blindsquirrel]

Is it a truck TB, like what the TBSS used stock? Aren't those things like ~$100 brand new?

[cabech984]

Is it a truck TB, like what the TBSS used stock? Aren't those things like ~$100 brand new?

I think that it is, but I'm not 100% sure. I definitely thought of throwing a new one on to rule it out, but figured I'd give diagnosing a shot. I added TPS voltage PID to my vcm scanner and its showing zero voltage at any throttle position running or not

[blindsquirrel]

https://www.rockauto.com/en/moreinfo.php?pk=5428311

The TPS/side cover is also available but honestly the whole thing is so cheap... there's usually some wear/slop in the bull gear that goes between the motor pinion & the rack gear, and that gives a flutter in the TP output.

[cabech984]

https://www.rockauto.com/en/moreinfo.php?pk=5428311

The TPS/side cover is also available but honestly the whole thing is so cheap... there's usually some wear/slop in the bull gear that goes between the motor pinion & the rack gear, and that gives a flutter in the TP output.

I actually just ordered an oem gm ls3 throttle body. I’ll see how things go when it gets here next week! The people who make the x-link recommend gm brand throttle bodies. Figure buy once, cry once. It’ll work with forced induction too, which is in my winter plans

[blindsquirrel]

Hitachi is the supplier for the TBs that GM installs at the factory...

[cabech984]

Hitachi is the supplier for the TBs that GM installs at the factory...

I didn't know that. I was watching some videos regarding GM vs Parts store throttle bodies, and they didn't appear to be the same when they were disassembled. Not sure if that applies to every brand of them though. I also don't have first hand experience with this. I might disassemble this one to see for myself!

[cabech984]

Just wanted to report back that the new throttle body seems to have fixed my issues. I disassembled the non-gm throttle body that I had on the truck, and it appeared to be a quality piece