GTA1990

iTrader: (1)

Chasing out the gremlins in my LB9 T5 Trans Am; she's getting there but man is she fighting me.







I've noticed my idle is never rock solid; the tack needle dances ever so slightly. I have a scan tool and the RPM's on the tool also move up and down. As for example, full warm, the ECU is commanding 550rpm. The idle will go slightly higher to 575 and lower to 525. Car has about 115k on it.


Keen to hear about what's considered a normal idle condition with these cars. Do they hover about the commanded idle speed or are they, like newer cars, rock solid


thanks

GeneralDisorder

iTrader: (1)

That's normal. The fuel mixture control is bouncing between rich and lean. This action energizes the catalytic converter as some of its function require more oxygen, and some requires more fuel. This has the effect of slightly increasing and decreasing the idle speed.

You really shouldn't feel this though. If the engine is running smoothly it's barely perceptible.

GD

ULTM8Z

What you can do is increase the throttle blades opening a little and reduce the IAC counts. Engine Will depend less om the ECM to maintain the idle speed. You'd need a scanner to do this though.

GTA1990

iTrader: (1)

thanks guys
Glad to hear its not way out of the norm. IAC counts are low 20s/ high teens on warm idle. What would you recommend adjusting it down to?

ULTM8Z

I run as close to 0 in park as possible. In drive I get about 10 to 15 at 675 rpm.