Shuddering problem

xurbanx · 01-02-2009, 09:50 AM

Couldn't think of a way to explain the situation in the thread title, hope it's not misleading.

What's happening with the Fiesta now is that, whenever I'm on the brakes (usually at the lights or drivethrough), the revs drop and increase from 1 down to .5 then back up again. It'll keep doing that as long as you have the brake depressed. Also if I let off the brake for a bit, the car will shudder/jerk along with the revs.

Does anyone know what the issue might be? I'm taking a stab in the dark that it might be the sparks or the leads?

290v · 01-02-2009, 05:31 PM

stab in the dark most brake boosters work of the Vac. hose attached to the inlet of the car engine check there isn't a split or hole in this hole also but clamp the hose off that goes to the booster and see if it still does it at idle (Don't drive it because your brakes might not work) there might be a faulty booster

amcqu2 · 27-02-2009, 09:39 PM

yeah i know this thread is a bit old but i had a similar thing. not as bad as in this aforementioned case but similar. whenever it would idle the revs would go up and down all the time. i finally decided to check the spark plugs and there was the problem. one of the factory plugs had a gap near 2.0mm instead of 1.3. all of the other sparks gaps were out as well as uneven wear on the electrode. since replacing these and getting a new air filter it runs like new. even getting better fuel economy now days which is a real bonus.