AquaJ

OK I've got a problem that makes me starching my head... The car in question is a 89 S5 TII with stock drivetrain and ECU. Car runs and drives well, but when it's fully warmed up and idling it will *try* to idle at ~1000 rpm, mostly smooth with a gentle and occasional *cough*.
Now is the weird part: when I manually force the engine to rev lower than 750(i.e. in gear and half-bite the clutch with engaged e-brake), it will ALWAYS goes back to 750 and idle perfectly smooth there and stays there, but if I rev the engine up a bit it will go back to the previous 1000 rpm idle mode.
Both idle modes are stable by themselves..........O_o

additionally, the 750 idle speed could be slightly adjusted via BAC valve, but the 1000 seems inert to BAC adjustments.
and my narrow TPS is actually dead on 1K. I don't have a Mazda dual light tester though...

Any thoughts?
Thanks...

RotaryEvolution

iTrader: (30)

throttle cable is taught, throttle body shaft is lightly binding or your thermowax is out of adjustment or sticking open slightly.

generally this is a thermowax issue but could simply be someone adjusted the throttle cable too tight. the throttle shafts sticking is uncommon.