My 96 2.6 Avant has developed a engine idle prob, at times for no reason the revs will increase sometimes up to 2000RPM. It will then drop to almost nothing and recover or cut out, it will restart straight away
If your sat at the lights with your foot on the brake the prob seems worse but at times it will run as it should. It runs fine other than that. any ideas anyone.

 

If your brake seems to affect the idle I would check your vacuum hoses for leaks. Also You may want to run some fuel cleaner through your engine. Sticky throttle and or idle valve would also cause your troubles.
Hope this helps.