Weird high idle?
#1
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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.
-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.
Last edited by Kfxguy; 06-25-2024 at 09:12 AM.
#7
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here’s a log and tune file.
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#8
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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.
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.
#9
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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.
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.
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.
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Kfxguy (Yesterday)
#11
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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.