Hi. I'm driving a 5 speed v6 Mustang. Twice in the last week the car has got into this state where the RMPs become very sporadic (so the car is randomly pulling and then slowing several times a second). At one point I was at the light idling and suddenly the RPMs wanted to rev up to 3 or 4 thousand RPMs, followed by wanting to stall. This lasts for anywhere from 3 to 10 seconds and does it a few times before returning to regularity again. While it is in this state, the check engine light starts flickering rapidly. Once the car settles down the check engine light is off again. I've replaced my spark plug wires and spark plugs relatively recently. Most of the time the car is fine - this problem is intermittent. Any ideas?