Can anyone tell me what went wrong?

[delbert62]

I just got a wideband a couple of weeks ago and decided to play with the tune last weekend. Long story short, I couldn't get the AFR below 15, so I checked the fuel pressure to see if my injectors were where they needed to be. They were slightly lean so I lowered the scale slightly. When I restarted the car, it ran fine for about a minute then the idle ramped up to about 2300 rpm and hasn't come down since. I tried reloading a previous tune that ran fine before. No change. I let it cool over night and restarted it. It ran fine for about 30 seconds and right back up to 2300 again. I feel it must be a mechanical instead of a tune issue but not sure where to look. Here is a short scan (I didn't want to run it too long at that high of idle). Any thoughts would be appreciated.

[delbert62]

I may have found the problem. I disconnected the fuel line and hooked it back up. It started and idled as it should for about 5 minutes. It must have had an air lock in the fuel line from when I hooked up the pressure gauge. I'll check it out more tomorrow and post an update

[delbert62]

Went back out today and started it back up. It didn't start right away, but after a few trys it did. Ran perfect for about 7-8 minutes and then the idle went up to 2300 again. I tried to get a log on it but I hit the wrong button and closed it when I wanted to save it. I did a read entire on the ecu and I will post that. I feel like it is a sensor or a fuel problem but I can't put my finger on it. I will let it cool back down and try it again (this time I will save the scan).

[xtremesilvy]

is it popping up a reduced engine power? any mods to it?

[delbert62]

The only code it is throwing is "idle too high". It is a 5.3 with an LS6 intake manifold, cold air intake, and short tube headers.

[gagliano7]

See if you have a vacuum leak.

[delbert62]

No vacuum leaks. I am going to pull the IAC off tonight and see if it is working properly

[delbert62]

Just replaced the IAC. Absolutely no change. Luckily my son loaned me the one off of his car so I'm not out $120 bucks. I did a "Write Entire" with my original base tune. Still no change. I hooked up the wideband and it is reading about 16. Fuel pressure is solid at 55. This has got to be something mechanical but I can't find it. Could really use some help.

[delbert62]

Latest update. I thought there might be a vacuum leak from underneath the intake so I pulled it and replaced the intake gaskets. No change in the idle speed (still 2700-3000) but the AFR dropped to 14. Loaded the SD tune to disable the MAF. Took off the intake tube between the throttle body and the air cleaner. When I partially block the hole in the TB where the IAC draws in from, the idle comes down where it should be. So the air "leak" is all through the IAC. Why would the IAC not be closing back down? The IAC does open and close when manually commanded through the Scanner VCM controls. The only thing I noticed in the tune was the "IAC reset position" is set at 160 where most stock tunes appear to be at 310. I have not recently changed this setting and it run fine before. Any thoughts?

[cesar]

Latest update. I thought there might be a vacuum leak from underneath the intake so I pulled it and replaced the intake gaskets. No change in the idle speed (still 2700-3000) but the AFR dropped to 14. Loaded the SD tune to disable the MAF. Took off the intake tube between the throttle body and the air cleaner. When I partially block the hole in the TB where the IAC draws in from, the idle comes down where it should be. So the air "leak" is all through the IAC. Why would the IAC not be closing back down? The IAC does open and close when manually commanded through the Scanner VCM controls. The only thing I noticed in the tune was the "IAC reset position" is set at 160 where most stock tunes appear to be at 310. I have not recently changed this setting and it run fine before. Any thoughts?

you have too much RAF

[delbert62]

you have too much RAF

Thanks cesar
Do you mean "Running Airflow"? I have not touched that. Would the requirements for that change?

[cesar]

lower the base running airflow in the idle tab by .7 and see if there are any changes. rinse and repeat until better.

[delbert62]

Well! After all this run around for the last couple of weeks I think I have found the problem. After reading a post on an old LT1 forum that sighted low battery voltage as his problem way back when, I went out and put the charger on over night. My battery voltage before charging was 12.2. After charging it was up to 13.3 volts. I started it up. It ran at about 15 for a minute and started searching. I shut it off, restarted it and it ran at 700 rpm for 45 minutes no problem at all. Can anyone tell me what field controls Idle vs. system voltage? What is the threshold for the idle to rise and by how much.