Lean at idle

well maybe you have a bad O2 sensor since is does this after it warms up.. I think thats when the ECC starts looking at the O2 sensor. Pull the codes and see whats there..

You may have inmetered air getting in.

Are you reading your a/f from a wideband?

The A/F gauges that use the O2 sensor signal will jump all over the place. The reason is that the O2 sensors "switch" between
.2 volt lean and .6 volt rich with a curve that looks like the drop off a high cliff. The curve is almost straight up and down, so the
voltage shoots from .2 to .6 and back down . again 2 or more times a second at cruse. You won't get much useful information
except when the mixture is extremely lean or extremely rich, there is no middle ground.

In other words, it is a pretty light show, but useless for tuning or diagnostics.

Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.

Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

See http://www.troublecodes.net/Ford/





IF your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.



89 through 95 cars have a working Check Engine light. Watch it instead of a test lamp.



Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

For those who are intimidated by all the wires & connections, see http://www.actron.com/product_detail.php?pid=16153 for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see http://www.midwayautosupply.com/pc-7208-90-equus-digital-ford-code-reader-3145.aspx – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

With all the mods you have, you need a tune no way around it.

Matt