during city driving my el willidle fine at around 600, its a auto, then suddenly it wont idle at all and stall, i have watched it dropped to under 500 and almost stall so rev it a bit and it goes upto 650 700
when ever it stalls it starts again and runs fine then suddenly it does it again
could this be the throttle position sensor
if i put the aircon on it doesnt seem to do it, it stays higher in the rev range

Start with simple things like checking for vacuum leaks then clean the ISC and throttle body. If still the same try replacing the plugs and possibly leads depending on how old the leads are (If the leads are 5 years or older I'd replace them). Might be worth trying another MAP sensor too.

First run a ECU fault code check,.

I had a similar problem many years ago when the El falcon had about 85000km on the clock. Ran the ECU check came up with Oxygen sensor reading High. Replaced the oxygen sensor and has been all good now for another 110000km. A O2 sensor always reading high when engine at operating temp will make the ecu lean out the fuel at idle causing low/stall problems.

A Vacuum leak from the inlet manifold gasket(which I had about 150000km) will cause a very rough idle and hesitation of the mark, only comes about once engine at operating temp.

Other than that spay out your ISC and throttle body with a can of carbi clean. Best to remove your ISC valve at the top of the throttle body. Just get a new gasket form ford or use some gasket paper or a cornflake box cardboard and cut out a template.

Also replace your fuel filter if you haven't done it in the last 80000km..

cheers........