Quote Originally Posted by Nomad9 View Post
Hi Hobbes,
This wouldn't be similar to an 86 3.5 would it? A lot of what you talk about sound familiar.
Looks similar under the hood but very different.
On the early system idle is set by:
Setting correct advance at 600rpm with vac tube disconnected.
Reconnect tube and set idle using the air bypass screw on the plenum to 700>800rpm.
Adjust idle mixture to 1% CO2 or less using mixture screw next to afm.
Bit of juggling often required re last two steps.

To maintain idle under various conditions there's an extra air valve thats controlled by coolant temp and air temp from the afm, and additionally on air con vehicles a solenoid valve that opens to bump up idle when the a/c is switched on. Plus the ecu will also fire the cold start injector if required.

Apart from the obvious mechanical difference of flapper versus hotwire the later 14CUX processes various sensor inputs and then controls idle (above base) using the idle bypass valve (which is a stepper motor) and by lengthening the injector pulse width under cold start conditions.

(And just to correct myself! - base idle on the later systems should be set according to manual at 450>550rpm - not 800 but as noted by PhillipA 600 seems better and on my manual trans I set at 650 as its a bit less prone to stall)