Weird rough idle issue.

[Whamhammer]

Hey all,

After I do a cold start, and the car warms a bit, if I drive the car, and the car hasnt totally come to full operating temperature, and I come to a stop for more than 30 or so seconds the idle gets really rough, and the idle kicks up for a moment, comes back down, and the roughness goes away. The tach rpm speed stays the same for the idle (except for the short moment it goes up and back down).

No codes, the tuner did give the o2s more time to warm up before the computer tripped a code because of the LT headers.

I have Seafoamed it since the problem showed up, in case of something gumming up the works, and I cleaned the throttle body. Air hoses and connectors are all attached, and MAF screen has been cleaned since.

Anyone got ideers?

[Naaman]

IAC?

[Whamhammer]

IAC?

Thats what I was thinking at first but wouldn't it set off a code?

[SMWS6TA]

Not necessarily, I had a broken MAP sensor and an 8" vacuum leak that didn't trip any codes.

[Whamhammer]

Not necessarily, I had a broken MAP sensor and an 8" vacuum leak that didn't trip any codes.

Is there anything special to changing an IAC these days? On my old TPI, it was replace IAC, and drive for 30 minutes so the computer will learn the new motor setup. Do we need to do anything more than that now?

[Naaman]

In my case, it was a broken o-ring. Replacing that solved the problem. I do believe that it could throw a code, but I don't remember whether I was getting a code when I had the issue (I think I was, because otherwise, I probably would not have been able to isolate it to the IAC... didn't even know what an IAC was, honestly).

As for the valve itself, it appears to just be bolted/screwed into the throttle body, with the sensor plugged into it's other side.

Looks simple to me (which is saying something

[Whamhammer]

In my case, it was a broken o-ring. Replacing that solved the problem. I do believe that it could throw a code, but I don't remember whether I was getting a code when I had the issue (I think I was, because otherwise, I probably would not have been able to isolate it to the IAC... didn't even know what an IAC was, honestly).

As for the valve itself, it appears to just be bolted/screwed into the throttle body, with the sensor plugged into it's other side.

Looks simple to me (which is saying something

As long as I dont need to do anything with the computer when I swap out the IAC, I can certainly swap the IAC out. Driving for 30 minutes isnt an issue for the me. I just want to make sure that I do it right.

[SMWS6TA]

nope just need a torx bit to remove the screws. I usually clean out the hole it goes in if I see a lot of oil build up.

[Whamhammer]

nope just need a torx bit to remove the screws. I usually clean out the hole it goes in if I see a lot of oil build up.

Awesome, thanks for the confirmation.

Why would you think you would see a lot of oil buildup on an LS1? Its not like the PCV system should have a catch can or anything on it.

[GTP231]

Get a can of 2+2 and spray around the intake manifold gasket area and all vacuum lines as well to rule out any vacuum leaks

[Whamhammer]

Get a can of 2+2 and spray around the intake manifold gasket area and all vacuum lines as well to rule out any vacuum leaks

Ive done that once since the problem began, when I Seafoamed the car, didn't see anything but it wont hurt to do it again.