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Discussion Starter #1
I have a 2001 ZX3 (zetec) manual transmission with 164k miles

Today on the way to work I noticed my speedometer started jumping when I press on the throttle and the engine would stutter and surge when this happened.

If I just barely press on the pedal to maintain speed it is fine, and if I very gently press and accelerate slowly it seems ok, but if I push down more than just a little the speedometer jumps 10-15mph and the engine stutters. The speedometer will return to the correct reading and the engine resumes normal operation when I ease up.

No warning lights have been illuminated.

I do not have abs or cruise control or factory radio

The engine revs normally and smoothly with no load.

I set the parking brake, pressed the throttle and slipped the clutch for a few seconds to put a load on the engine, it ran smoothly under load for that time with the car not moving.

Car idles normally

Everything I can find points to the speed sensor. I can't get under the car right now at work, but from what I can see from the top (it is short and looks like a bolt is holding it in) I am pretty sure I have the gear driven one so I had to order it. I will hopefully get it changed tonight and see if that is the problem.

I am just looking for other possibilities in case this is not the issue. This is my daily driver for 105mi a day and I can't afford to have it down.

Thanks :)
 

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Prior to yesterday, I would have not suspected a bad VSS causing those symptoms. Dirty VSS maybe, bad VSS, no. But, yeah, your car is acting like a bad VSS. hmmmm? I have always thought sensors like that were rock solid and good for 50+ years... unless hit by gear-teeth or gunked-up.

Then I read a thread here (yesterday?) where one guy (then a second guy!) claimed to have fixed similar(?) symptoms by replacing the VSS.

"a gear driven VSS" huh? really? Some Foci have that? I am seriously ignorant or un-learn-ed or some of each. I gotta go look into that subject.

The pic below will help you very little; sorry pic is an auto trans.
 

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The VSS does not seem to be physically gear driven, but that is the nomenclature used in the description. Go figure. Anyway, not the problem, now I am really stumped. Symptoms show up stopped now. Might be coil pack but mine ohms out ok Don't want to just keep throwing money at it. Electronic parts are not returnable. Ugh!
 

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The vss isn't your problem if the speedo "jumps". Your issue is the coil pack. When the vss fails, your speedo will drop to zero and your odo will read 3 dashes instead of a number. Change your coil pack.
 
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