Throttle Sensors vs Wire Round 7

Been a lurker here since I bought my lady a rather clean 2012 Tahoe LS three months ago. 156K miles.
I'm above average mechanically inclined for being a [cough] mellenial, but untill now have always run older vehicles (IE a 263K 97 Burb) for ease of repairs and noted lack of sensor issues...

Two weeks or so ago, Check engine light came on and went away in the same drive. I checked with my entry level scanner anyway. It gave P0121, Throttle/Pedal Position Sensor/Switch A Range/performance problem. General online consensus is clean the throttle body.
I put it off (NOT ADVISED!!) then two weeks later, it went into limp home.

The DIC told me:
"Reduced Engine Power"
"Service Stabilitrak"
"Service [something else]"

The wife told me:
"This better not be from running it in M5 mode!!"

In addition to low power, it was lurching badly when downshifting from 2nd to 1st and worse when coming to a stop in 1st.
The scanner gave P2135 "Throttle/Pedal position switch/Sensor A/B Voltage Correlation"
I yanked the throttle body off and cleaned it. Smacked it back on and attempted the 3 minute idle-1 minute rest-3 minute idle-drive above 45 for a few relearn procedure. Limp mode was gone, however it still was lurching.

Okay, improvement, but not fixed. I got home, shut it off.

Now here's the recurring problem:
Immediately after, I restarted just for the heck of it and it flew up to 3000 RPMs at idle, slowly climbing to 3500. I shut her down and went inside to scratch my head.

I ended up replacing, in order, the TB postion sensor, the connector at the throttle body-soldered (live data showed the TB % jumping around while I wiggled it), and Pedal Position Sensor. All ACdelco except the Throttle Body Position sensor, which is Duralast. I tested the Duralast unit while on the truck through the new connector with my multimeter and it seems A-OK. I have an ACdelco TBPS too just in case.

Before each replacement, i disconnected the battery and let the engine cool overnight. After each replacement, the EXACT same 3K idle problem occurred after attempting the relearn. It's always when engine is hot after the drive portion of the relearn.

I remembered to replug in the PCV line before swapping the connector. May be responsible for the early P0300 misfire code, not sure?

I've got the following codes right now:
P0122 Throttle/Pedal position Sensor/Switch A circuit LOW
P0233Throttle/Pedal position Switch/Sensor B circuit HIGH
P0300 Random/multiple misfires
P0507 Idle RPM higher than expected (no kidding)

Now I'm thinking that either:
A) relearn procedure is not working correctly, I'm not really willing to see if it "figures itself out" while acting like that (3500 rpm) and throwing codes.
but more likely
B) I've got a phantom bad wire. The wire split loom absolutely crumbled where it ran above the valve cover.

I had put off investigating the harness because swapping sensors is easy. I checked about 2 feet of it from the TBPS to the back of the valve cover and it visually looks fine, just a little dirty.

I also haven't replaced the throttle body itself (don't know how to test), or the PCM. Both of which are on the list of possibilities.

I figured I'd ask the giants here so I might stand on a shoulder...

Thanks in advance!

If you replaced the TPS already, make sure it is installed right. I believe you need to open the throttle fully when installing.
Do you still notice the sensor data jumping around when you wiggle the wire?

Thanks for the reply!

I was careful to open it while installing but now I'm not 100% sure. I'm going to try again right now.

My scanner shows a ton of stuff for being so cheap, I just don't know what the abbreviations mean

Do you have a scanner recommendation that won't break the bank?

with fly by wire stuff I don't even try to fix tb or pedal when they go into reduced power more. Just toss in a new oem of which the code says.


so far it's always fixed them.



on a side note I know there was a thread a few months back where a guy said the more he ran the idle relearn the worst it got over time. I'm not sure what to search for thou.

mikez71 said:

If you replaced the TPS already, make sure it is installed right. I believe you need to open the throttle fully when installing.
Do you still notice the sensor data jumping around when you wiggle the wire?

Click to expand...

Just saw that last question- no, after replacing the connector, the change from wiggle apparently disappeared.

j91z28d1 said:

with fly by wire stuff I don't even try to fix tb or pedal when they go into reduced power more. Just toss in a new oem of which the code says.


so far it's always fixed them.



on a side note I know there was a thread a few months back where a guy said the more he ran the idle relearn the worst it got over time. I'm not sure what to search for thou.

Click to expand...

I def agree. I have never had a problem with drive by cable on my 4 vehicles that had it. All over 150K, most over 225K.
I was more trying to troubleshoot after the expected replacement didn't work...

mikez71 said:

If you replaced the TPS already, make sure it is installed right. I believe you need to open the throttle fully when installing.
Do you still notice the sensor data jumping around when you wiggle the wire?

Click to expand...

Well shoot if that didn't seem to work!! I just got back from the drive and it *DID NOT* over rev on idle. Its still a little lurchy but I think that will (hopefully) sort itself out.

MikeZ71, THANK YOU SIR!

OBSalsoNNBS said:

Well shoot if that didn't seem to work!! I just got back from the drive and it *DID NOT* over rev on idle. Its still a little lurchy but I think that will (hopefully) sort itself out.

MikeZ71, THANK YOU SIR!

Click to expand...

I'm tagging @mikez71 to be sure he sees this. When you tag a member, start by typing the "@" symbol, then start typing the username. A list of matches should display and you can pick the correct one on that list. Otherwise the target member may not see your post.

Glad it seems to be working, thanks for tagging it for me Fless! This board is a great resource! I try to fill in what I can to give the old regulars a break. Its usually stuff I read about from here!

Ay! The problem is back... Slightly different, revs on startup to 1500 for 1 min then up to 3000. I'll update once I find the solution for those who see this thread in the future...