club.liberty.asn.au

I've noticed my car has a rough idle at times, like it's hunting for the idle rpm. Only really noticed it after the downpipe.

Would resetting the ECU help? or not realy?

Many cars with mileage high do this (MX5, some Porsche, Discos) , and usually its due to gradual carbon buildup in the idle stabilizer (think of a taper going into a hole to adjust air bleed past throttle plate, based on signals from tacho/ecu). Any crap in there makes idle unstable.
Also can be caused by an air leak on the intake side somewhere - in this case, try spraying something like wd40 onto small areas of the intake joints, and see if the idle changes due to either blocking the leak, or sucking in the spray. COmmon fix is to flush some cleaner type solvent through that area - MX5 actually have a fitting to make this easy....
jp

I was thinking it had to do with either the downpipe or the AFM... but hmm vac leak hey? I haven't touched any vacuum lines!

I thought it was my BOV on full-atmo at first, but nope... that's not it...

A turbo will obviously have more things that can go wrong, but at idle there should very little boost. I would try the spray thing first, as its easy to do and requires no knowledge of whats going on inside. If you could identify the idle stabilizer unit, you might check it for leads connected, hoses ok etc. A leaking exhaust could also cause something here - any noise or smell that might be such a leak?
Have you tried to get an error code out of it? I wonder if the same method as my OB works on a GT? Under the driver knee panel there are two white wires, unconnected - plug them together, turn on, hit the trip reset button while gauges are sweeping, and codes are displayed one at a time, push trip button to go to next. P codes are powertrain, C are chassis.
Anybody know if this works?
jp