Help? Shunting sensation

[Kitty]

I have a 1996 ford mondeo lx 2.0 zetec engine 4 speed auto, 196 xxxkms on the clock! The problem is that when driving it will sometimes shunt. It almost feels like it's breaking quite quickly and only lasts a second. It might do this quite a few times a minute. Being my first car and quite inexperienced with mechanics, I wouldn't have a clue where to start looking for the problem. The revs drop by 500ish then straight back up. It also varies when it does this (some drives it will be fine and some times it will do it). It used to do this when at a certain speed( 70-90kms), thought it could have been the car deciding which gear to stay in but now it will do this at anything above 40kms. The engine isn't going passed normal temperatures either.
Could anyone give me advice it what it might be. Gratefully apprectiated

[tut0r]

Is the car shaking at idle or any loss of power present? Pulling to one side at all?

[Kitty]

Nah it's fine at idle. Just got a new air flow sensor put it because it was idling really rough. The idle is fine now. Although after going for a long drive, when it idles, the sound that comes out of the exhaust is like a putt putt putt, the revs are at the same level, 900. The shunting almost could be a loss of power although it lasts for a second not to sure

[cobrin]

tough call but if it's missing for a second or so it's not a little misfire, little misfires usually are a hesitation or the like.

at the cars age and K's I'd suspect some sensors starting to become a little sus. which could explain a new air flow sensor previously.

Cam Angle sensor or Crank Angle sensor can do your symptoms but it's jumping the gun without further diagnosing.

could start with the usual suspects plugs/leads ect...