A couple of issues....

[zerovandez]

I am of course assuming you verified power to the OBD Link MX after you move the shifter out of park.

Yeah theres always power and Bluetooth regarldess of shifter position. OBD Fusion fails after trying to get vehicle data. I test the adapter and app with 2 other cars and it works while driving. I was reading up a little on the #2 pin which is a SAE J1850 BUS+ that provides communication to the ECM. The iDatalink module is a bypass module which might be interfering with coms is what I am assuming but I originally thought that it would only be active when the alarm is armed. I think I just spliced into it with a connector so it should be easy to undo and will get to it tomorrow.

 

[TJBaker57]

So let's drift back to the subject. Unexplained fast idle speed. There is a PID for desired idle speed. It comes with the Torque App Extended Pid set for GM. Seems to work OK on my 02 4.2l Trailblazer. With this one might determine if the fast idle is being commanded or happening outside of the PCMs desires.


Setup for OBD Fusion w/J1850 VPW 10.4k Bus:

Name/Description: Desired idle speed
Units: RPM
Module/Header: ECM
Mode 22
PID 119201
Equation A*12.5

Priority is at user discretion.

 

[zerovandez]

Yeah, there's power and BT to the adapter when out of Park. My phone can connect to it but OBD Fusion will not read vehicle data then disconnect.

Well, I completely removed the bypass module from the OBD lead pin 2 and still having the same communications issues.

 

[TJBaker57]

Yeah, there's power and BT to the adapter when out of Park. My phone can connect to it but OBD Fusion will not read vehicle data then disconnect.

Well, I completely removed the bypass module from the OBD lead pin 2 and still having the same communications issues.

So it works normally in Park but loses comms anywhere else!?!? Wow! This is truly weird. This seems likely to be an issue unrelated to your running hot, fast idle, and P0171/P0172 and thus may warrant a different/new thread.

 

[zerovandez]

Yeah I know. I'll be starting a new thread to address the OBD2 port issue.

As for high idle after prolonged steady driving - I will contribute this to cool engine temps. The other day it finally threw a P0172 code and it went away on it's own. When the code triggered the ECT needle was just above the 1/4 mark. I looked up the code and this is the root cause for GM

Engine running at steady speed in closed loop, IAT sensor input from 14-158°F, BARO input over 75 kPa, fuel tank level over 25% and the PCM detected the LONGFT value was over -30% for 5 seconds, or the SHRTFT value was over -20% for 45 seconds

So during my 40 minute commute - these conditions were all met. I'll change the ECT and thermostat as soon as it drops in the mail and hopefully we can resolve this thread.

 

[zerovandez]

OBD2 port resolved lol. If you're curious....

SOLVED! - Strange OBD2 Port Issues

I'll keep this one short... Cold start, while in Park, the OBD2 port responds as normal. As soon as the shift lever leaves Park and goes into Drive, the port still provides power and does not communicate with any scanner. I had an iDatalink bypass module connected to Pin 2 of the OBD2...

gmtnation.com

 

[zerovandez]

Welp. Im in the middle of changing the thermostat. Going well. But...the ACDelco thermostat in there now is not in any way stuck open. I have been monitoring temps via BT app and it stays rather close to 175 on average. Im going to take a wild guess and assume that this is just defective in opening temps and just move onward with replacing. The replacement is a GM unit which for the most part looks just like the ACDelco.

 

[Mooseman]

That's exactly how mine was. Looked fine when I pulled it out.

What did you do to your GMT today?

Oil and filter change.

gmtnation.com

 

[Blckshdw]

+1 Mine also looked "normal" when I removed it, but was running about 185 tops. New one looked exactly the same, but temps got up to 195 and held steady after 10 minutes idling.

 

[zerovandez]

That ECT sensor. What a pain the the @$$ that was! Ive got a pretty extenstive resume with rebuilding honda engines and cars even up to working on an annoying Audi but the ECT in this truck by far is the f’in worst thing ever!

Anyhow, burped the cooling system. Temps reached 175 rather quick, 68f ambient, reved to 2k for a couple of minutes, no leaks, temps got to 202f! Drove the car for 30 mins and temps look good - in motion around 195-198. Idle at 201 steady.

The other day, parked the car, engine revd up and died. Pending code for camshaft pos sensor so I have one on the way. At some point Im going to test fuel pressure as well to rule out fuel delivery as causing any issues.

 

[zerovandez]

Just wanted to update this thread with results.

Since the thermostat replacement - things seem better. Fuel trims are much closer to zero and throttle response has much improved.

I did get a leak from the new ECT - couldnt torque it down enough to get a proper seal. A crows foot did not work well for me. I couldnt find a slotted 18mm line socket. I didnt care to cut a socket either. I used an open socket set from HF

SAE and Metric Go-Thru Socket Set, 21-Piece

Amazing deals on this 21Pc Sae/Metric Go-Thru Socket Set at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

I cut the ECT wires to be able to pass them through the socket then crimpred them with weather proof connectors to the orignal gm connector after I was done tightening the ECT. Temps are now consistent at 198 driving, 201 idle, and 207 up hill for a longer period.

The only issue I have now is hard starting after getting a tank fill. For some reason my fuel pressture tester is not fitting onto the shrader valve properly and will monkey around with it later.

So far so good. Thanks guys!