Dear all,

I'm new to this forum, stumbled on it whilst googling for a solution for my Mk2 1.6 October 2005 Focus.

I just bought the car and then when testing it for about 10 minutes I didn't notice this, but the engine hesitates whenever I'm not accelerating or accelerating mildly.

when driving on uneven pavements the hesitation is still there but one might not appreciate it is there due to the shaking of the vehicle. This is probably why I didn’t notice it when test driving it.

On the way from the (independent) dealer via the motorway I noticed this hesitation immediately.

I complained to the dealer and they without hesitation asked for the car back, but I still notice this even after they saying that the problem was the new Bosch sparkplugs they fitted when servicing it. Apparently the problem was fixed with new NGKs

This time it did feel like the problem was fixed or at least minimised. But soon after, on the motorway, I noticed the problem again.

Back home and looking under the bonnet it looked like they also have replaced the ignition leads as the lettering on them is very white. The coilpack is still the old one.

More recently I asked a colleague who is into motor racing to have a look and he drove the car for a couple of miles, immediately feeling the problem. It is ever so subtle most of the time but it is there.

However what he noticed was that the hesitation seemed to be always with the accelerator pedal in the same angle or position. Thinking about what he was saying it made sense with what I had been feeling since the beginning. The hesitation doesn’t happen when the pedal is pushed a bit further.

This could be the TPS (throttle positioning sensor) he said or the throttle body needing a clean….

I have a cheap OBD tester and checked the throttle position percentage – here is where I have doubts:

-          When checking the TPS in percentage, it is a fixed value when key is in pos II. Moving the pedal does not change it. Is this normal on this car model? I have had other brands and it moved.

-          When engine is running the percentage varies with the pedal position.

-          Idling the percentage is 15.7 to 16.1

-          Pressing the pedal ever so gentle it jumps from that value to around 18 to 19%.

-          If I press just slightly farther the percentage could go up but also down…. Strange yes

-          If I press even farther it goes up to 20% and holds it steady if I don’t move the foot.

-          Pressing a bit more makes the % go up through all expected values.

Could this be the problems?

Or could there be any other component failing? The car is still in warranty so I would appreciate any push into the right direction. Just taking the car back doesn’t seem to be helpful since they might not be looking at the right fault location?!

Someone a bit more mechanically minded will surely have the answer but thinking logically, from what you've said about the tps %age actually dropping slightly around the 18- 20% range, despite pressing the pedal further,  that would seem to explain it to me.

It's effectively as if you reach that point, then back off the gas slightly before pressing further and that's just what your engine sounds like it's doing.

Unfortunately I can't help with finding or cleaning the sensor, but as I say, there are a lot of brains living here =)