7mgte Lean idle


New Member
Authorized Seller
Jul 31, 2014
First off my car is a 87 motor is out of a 91 with a 91 ecu. i bought the motor fully built from a guy down in CT. I bought a new custom harness so the plugs under dash would be right
The engine has
550 injectors
lex afm
42 psi fuel pressure
Apexi neo piggyback
forged internals
running 8psi boost

The problem:
at idle before it warms up afr hovers around 14.7, after it warms up, it is off the charts Lean. (AEM-UEGO wideband) its happy cruising, and its happy under WOT boost (pig rich) but if i let it just sit and idle my wideband is at --- and the light is Red.

When it first starts the ecu is fine then i think something triggers it to go into limp mode
I've already tried unplugging the knock sensor, bypassing the vsv, unplugging the stock o2 all had no affect
I think the problem is something to do with the timing being thrown off by a sensor.
when i add loads of fuel with the neo i can get the afr to 16.8ish but it causes the idle to be low and have a lope to it.

NOTE: There is black soot building up on the bottom of the bumper right were muffler outlet is. I thought soot was from running rich not lean.

Any and all help will be much appreciated as i am trying to make it to a big regional car show next weekend and would love to get it running right before then