idle issues

[Victorma]

Hi, I have a, 2000 ford falcon AU series 2, intech 4.0.
Can anyone help with my high idle problem.
About a week ago, I started my car and its idle went straight to 1100 rpms, then settles at 900 rpms.

I have checked for leaks, changed IAC unit and checked for foulup in throttle unit but no change.
I voltage tested both new and old IAC and they seem to read ok.
Voltage reads, unplugged engine running, 13.6 volts and engine off 12.4 volts. ohms reads 356 but im not sure if its 356 -35.6 - 3.56 as my multi doesn't state this.
I also lowered the idle speed on throttle but it ran bad and then when i load test it in gear it wanted to stall. I also tested it with aircon on and it readjusted the idle up automatically, so at least that works. Im not sure what more I can do, I appreciate any help. Thanks

[Blue Dog]

Firstly, check for logged fault codes.
Then monitor the O2 sensor & fuel trim data.

http://fordforums.com.au/wsmpub/augx/Part%2010-1.html

[aussiblue]

I have checked for leaks,

How? It sound like an intake manifold gasket leak to me.

The inlet manifolds typically leak at number 1 and or 6 as the nuts on the manifold retaining studs there loosen over time and the very bottom parts of the gasket then burns out. Because only a small part of the gasket has burnt out, simply re-tightening the nuts won't fix it and you will need to replace the gasket remembering to torque to specification in a circular patter from the center of the manifold outward.

Note that the old pre-computerised fuel injection tricks of using/spraying engine start sprays, benzene, water, oil etc around the manifold will most often not work to find these leaks as: a) the ECU rapidly adjust for the change in air in the mixture and it's next to impossible to pick up any change in the engine noise or rpms using this old method; and. b) as it the lowest point of the gasket that burns out creating the vacuum leak, you are also fighting gravity with any gases or fluid sprayed around just falling to the ground rather than being sucked in where the small piece of gasket has burnt through.

Easiest and most effective to use a length of windscreen washer sized hose with one end in or close to the ear to listen for the no mistaking tell-tale sucking noise of a vacuum leak while poking around under the manifold at idle (with engine both cold and hot as the gap between the head and the manifold changes as the metal in the manifold and head expands and shrinks with heat and cooling). A smoke test will also work and a party fog machine can easily be modified (e.g. https://www.youtube.com/watch?v=j8o0YBoO7kw and https://www.youtube.com/watch?v=b4TBrF7k2YY) to work as a smoke tester and is healthier than using a cigar like Scotty Kilmar per https://www.youtube.com/watch?v=zMok2y05jNE ). Jaycar and Altronics have cheap Gog machines (e.g. https://www.jaycar.com.au/400w-mini-...03f0776574a552 . But using the length of tubing the ear is usually just as effective and much cheaper.

[Victorma]

Thankyou very much.
That was very clear and precise.
I will definitely change the gasket cos I do hear hissssing, but can't tell if its a leak or normal engine background noise. Thanks again.