2004 silverado 5.3. Installed a turbo. Rear o2 delete. I have not tuned it for boost, did not change the map sensor yet, have not changed injectors yet. I only installed a huron speed turbo kit, it has not seen boost yet, its just being driven normal until I can get to the rest of the install. No cam, heads etc. The engine is completely stock except for valve springs installed a few weeks ago (problem started after turbo install, no tune changes at that point). So the problem is, crank it up, rpm flairs just a little like normal. It comes down to to the normal 575rpm idle. After about a minute or so, the commanded idle rpm starts (I can watch it in the scanner) creeping up until it gets to 700rpm. If I lower the idle rpm by 100rpm (in the scanner or flash in the tune, HP tuners) it does lower it accordingly, it will idle at 475 for a little bit then rise ( I can watch commanded rpm in the scanner rise) up to 600rpm.
-No vacuum leaks. Its definitely tune related.
-my son broke the coolant temp connector in the driver side head, so I soldered in a new one. Reads correctly in scanner
-MAF is installed in the charge pipe with a 24" extension harness. Frequency shows up on scanner
- I installed a factory electric dual fan setup. Its currently wired to come on with the key (have harness for that, just need time to install) I have not added idle air in the tune for fans.
- Maf is about 12" before throttle body
-Blowoff valve is not installed (to keep out of boost) Its before the maf, I have a microfiber rag ziptied over the hole lol.
-fuel trims are normal. drives normal.


I looked through the tune and do not see anything that would make it rise like that. COT is turned off also.

 

Base running Airflow is off.

 

it’s not. I’ve change it and it makes no difference. The commanded idle slowly creeps to 700. And it idles at 700. I put it in SD and it still does it. I’ll post a log and tune file this evening

 

In your log, make sure you are logging dynamic airflow, desired idle airflow, STIT and LTIT, IAC desired and actual posistion.

 

I’ll double check. Thx

 

This statement here tells me it's off and you don't know how to tune it.

 

fair enough. But let me ask you. If the idle airflow is off, does the COMMANDED idle rpm change? Not the ACTUAL idle rpm. The commanded that you see in the scanner? Because as far as I know, it does not. I’m not simply having a high idle issue, I’m having a COMMANDED idle issue. I’m not commanding that rpm. The commanding and actual rpm do match. If I lower the commanded, it lowers the idle accordingly, but if I lower the idle where it is supposed to be (575rpm) and I lower it to 450 to get that 575, then upon start up, it will idle at 450 until the minute or so is up and then make its way up to a higher rpm.

here’s a log and tune file.

 

Your Base Running Airflow is off, it's that simple. Commanded you can put in all day but if the Base is off the PCM will not adjust properly to get that RPM.

Base has to be the proper values so the Commanded can take into account all the other stuff it needs to incorporate and make that idle happen. That Base Running Airflow is pretty important.

 

look, I appreciate you trying to help, and that’s what you probably think the issue is. But it’s not. I can raise and lower my base running airflow and the only thing it does is compensate with short term and long term idle trims. Like I said before, the commanded idle rpm goes to 700. It’s one of the channels in my scanner. I’m not referring to the tach rpm. Which is 700 also, but something is commanding the idle to rise. If I command it to 600 in the scanner, it goes to 600. If I raise or lower my base airflow, that does not have anything to do with the commanded idle rpm. I could put a ton of airflow in there and the commanded idle will stay the same but the engine rpm will likely go up.
im going to reiterate. This engine is stock. Stock cam, heads etc. there’s no reason I should have to retune idle all of a sudden just from bolting on a turbo. This is the third turbo kit I’ve done. The other two did not have any idle issues or need idle retuned. I’m no professional, and I don’t know everything, but I’ve successfully tuned dozens of vehicles. I’m just missing something. And I can’t put my finger on it.

 

I still think if the rear o2 delete is the only real tune related change that was made, it is time to undelete them and see if you are running into a weird diagnostics bug. I know you can weld in an extra bung somewhere to test this idea.

 

I plugged the sensor back in last night and ziptied it up. No change. I had done that with the other rear sensor a couple years ago because I didn't feel like welding in a bung and needed to use the secondary bung for the wideband. No ill effects there. At this point, I'm not sure whats going on but i do think its some sort of diagnostic bug. I'm gonna load a COS soon anyways so maybe that will get rid of it. But I'm pretty sure its not the base running airflow because I would not see a change in Commanded idle rpm, But I'd see a difference in actual rpm... Maybe I'm not saying it or describing it correctly is why the above guy keeps insisting that the base running airflow is the issue. I have messed with idle air and it did not change the commanded rpm that was displayed. No matter what, it reverts to 700 unless I change the idle rpm in the idle rpm table.

 

I never figured this out. It’s definitely not the running airflow like I said before. That would be impossible because when you change the amount of airflow, the commanded rpm does not change. The actual engine rpm might, but the set point in the computer does not change. I wasted my time fooling with idle airflow, as I knew I would. But leave no stones unturned.
I retuned the Ve. The maf was messing with it. I flashed a 2 bar COS for boost on speed density. Runs way better now that I have the maf turned off. Still has the stupid idle issue. I talked to a buddy of mine who’s a far more experienced tuner than I am, he’s a member on here, he said he tuned an 06 truck and it started doing that. He hasn’t figured it out yet either. He thinks it’s an hp tuners bug. I dunno.

 

I was just reading a thread in the HPT vcm editor forum where a guy claimed to have some tuning bugs when using version 5 that cleared up when he reverted to version 4. Who knows? Although now that I think about it, the only bizarre tune glitches I have encountered were after flashing with version 5.04. A reflash fixed them, so I just figured it was a bad write to my 20 year old PCM.