LS3 does not idle
 

I have a new LS3 427 which has been run and dyno'd. When I start the car it will idle around 1500 then after working the throttle it will pass idle and want to shut off. I have run it about 15 times up to temperature and I have heard it takes the ECM sometime to sync with the engine but you need to be driving it. One thing I find odd is when I put power to the car the throttle body flips open then back to closed, is that normal? Thanks

Sounds like a Vacuum leak............A friend just had a similar issue and we found the Vacuum port on the back of the manifold (manual brakes) was not capped off ................

Ken

thanks will recheck all the lines again

Should have stored a code. Vacuum leaks will cause the "too lean both banks" code. The throttle body blade opening and closing is normal.

I have no codes and thanks

IAC sounds like a culprit..

I'm assuming this is a factory style ECM? DBW throttle or cable? Does it idle at 1500 after warmup, or just cold?

If it idles at 1500 warm, that strongly suggests a vacuum leak, a throttle body blade sticking, or some very odd tuning. Or an IAC problem if this is a cable throttle body.

Notes: vacuum leaks will not always set a code, depending on how bad they are and how the tune is set up. Also the "learning" part of the ECM doesn't really affect idle parameters, just the fueling. And if you're using a MAF, and the engine has not been tuned with your particular air intake path, IMO you should get it tuned before running it really hard. The MAF sensor is quite sensitive to variations in the airflow path, and it is the primary determining factor in getting correct A/F ratio.

How big is the cam? MAF or Speed Density? What kind of base tune are you using? Do you know if you are running open or closed loop at low engine speeds?

Neil its a Blue Print Engine 427 FI with a MAF, specs are on their web site. I am told it needs to be running on the road so the ECM can adjust and it will not do that sitting in my garage. I have corresponded with another who has the same engine and it took about 25 trips to settle out,. That said I am not sure I drink the cool aide but Blue Print Engines is waiting for it to get on the road and go from there. The engine has been dyno'd so I am not sure...

Mine had a similar issue (LS1), it was the IAC wires.