05misfire

My 2005 cobalt ss lsj has a weird idle when I push in the clutch and it’s rolling and sometimes it will just be between 800-1000 and others it will go up to 1200 and as low as 700. It idles good when it’s stopped but it takes a different length of time before it gets to a perfect idle each time. It used to be worse but I cleaned the throttle body with a rag while it was on the car and it got better for about a week but still didn’t idle perfect. I’m just wondering if a unplugged o2 sensor would cause this because my downpipe only had 1 hole so there’s only 1 in. Just wondering if that would change the idle.

Slowbalt2000

iTrader: (1)

Which o2 sensor are you missing? If its the one after the cat then you dont need it. You definitely want to have the pre-cat O2 sensor installed.

05misfire

What would it do if it was the wrong one in. And I think it was the pre-cat sensor. Also I have a catless downpipe.

bubba_jay

iTrader: (1)

Are you running stock injectors?

05misfire

No I got 60lb ones along with the zzp stage 3 kit

slavik

This is exactly your problem. The 60lb Siemens injectors are the core of the rough idle problem,
due to their spray pattern - they don't spray 2 separate streams onto 2 intake valves, instead they spray 1 stream right in between the 2 intake valves, which is hardly ideal.
This forum has countless threads of people having idle problems with 60lb injectors. google: lsj 60 rough idle

More here: https://www.cobaltss.net/forums/tuni...cs-lsj-300942/ and here https://www.cruzetalk.com/threads/tr...uj-luv.224177/

jdbaugh1

iTrader: (1)

Split spray injectors may help but the tune can also cause idle fluctuations. Idle can be finnicky on these cars once modified. People have been able to get the 60lb. Siemens to idle nicely. My personal experience I originally had the Siemens which Trifecta could not get to idle properly. Then they had me upgrade to the split spray but it still idled the same. Now that I am using an AEM Infinity ECS I am using 1300cc single spray pattern injectors like the Siemens and it idles fine though I presumably have a lot more control over idle parameters and compensation methods than Trifecta did with my stock 06 L61 ECU.

However, there are ~60lb split spray injectors available if interested.