Chasing a likely air leak on my 91 GT I purchased new. Posting here as the IAC valves on GT and turbos are similar for this gen.
The 91 has a idle adjustment screw that provides fine tuning of the idle. Per FSM, it starts at 2 full open turns and then adjusted for fine tuning. Mine followed that, but 28 years later, it's now closed suggesting air getting in elsewhere.
I have replaced all vacum hoses and some all of the normal smoke etc tests to rule out any vacuum leaks. On a whim, I plugged the air intake for the isc and low and behold, the idle dropped 100/150. (Under normal, warm engine, when isc should be closed). Pulled the pigtail and the isc opened jumping the idle up 300-500 suggesting that the valve is operating.
So, when closed, should the ISC be 100% closed or should it leak?
The 91 has a idle adjustment screw that provides fine tuning of the idle. Per FSM, it starts at 2 full open turns and then adjusted for fine tuning. Mine followed that, but 28 years later, it's now closed suggesting air getting in elsewhere.
I have replaced all vacum hoses and some all of the normal smoke etc tests to rule out any vacuum leaks. On a whim, I plugged the air intake for the isc and low and behold, the idle dropped 100/150. (Under normal, warm engine, when isc should be closed). Pulled the pigtail and the isc opened jumping the idle up 300-500 suggesting that the valve is operating.
So, when closed, should the ISC be 100% closed or should it leak?