Hi,

I've got a strange problem on my 105hp 1.6 EFI ford escort '91

When the IAT (intake air temp) sensor is connected, the mixture goes very lean (lambda < 0.1V), and of course, driveability goes bye-bye...

When the IAT is disconnected, the mixture goes rich (lambda=0.9V), and the car behaves OK, but fuel consumption goes up.

Oxygen sensor is brand new.

What might be causing this, eludes me...

Possibly a faulty IAT sensor. Have you checked the resistance of the IAT sensor? Is it within factory spec?

yes, it's within specs

my guess is that, when IAT's disconnected, ECU squirts additional gasoline to make sure the mixture doesn't go dangerously lean... that's why the engine appears to be running OK while IAT's disconnected. But it sure isn't runing at optimum power&gas mileage.