This is what I have.....

Stock 2000 5.3 Vortec motor. It does have 1 3/4" long tubes to fit into my 69 Firebird. It has the PCM out of the donor truck and a harness by PSI and an AEM WBO2 - everything else is stock.

The motor idles fine. the problem is this:

If the engine is cold (has sat over night) the first try at starting it results in the engine just spinning without starting. The second try results in immediate start up and rpm flare and idle down to normal commanded idle rpm.

I can "bump" the starter without actually cranking the engine first, then when I try to start it will fire right up.

Once the engine has fired off, this issue goes away and cannot be duplicated until the engine has sat for several hours and returned to ambient temp.

Any ideas anyone might have to point me in the right direction?

One last bit of info - on initial start up the WBO2 fluctuates between 16.0-16.8 AFR and slowly settles to about 13.8-14.0 AFR after about 1.5-2.0 minutes of running. If it is already warm AFR stays pretty constant around 13.8.

Thx

D