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2005 Laguna II 1.9 dci Estate.

Driving to work everything is fine until I get into town, then I noticed that the temperature gauge was not working, needle rock bottom.

Engine running really rough at the lower round town speeds, reluctant acceleration, I can feel the engine holding back then a surge of acceleration then holding back, basically driving like a pig.

Finally got to work, engine seems to be ticking over smoothly, weird.

When I go to leave the yard, the car takes ages to start, I noticed that the coil light came on, taking a little time to heat the plugs, I thought it's never done this before.

When I finally got to my destination I investigated and found a single wire on the Temperature Sensor had broken and found the other wire to be very brittle aswell.

I ended up cutting the plug off and fitted a small new section of decent speaker wire with 2 small female spade crimps, plug it onto the sensor - diagonal corners and hey presto, Temperature gauge works, car starts immediately and no rough running at low speeds.

What had obviously happened was the ECU thought the engine was cold (temperature gauge at rock bottom) and had opened the egr to recirculate the exhaust gases, obviously a hot engine doesn't like this, hence runs rough.

When starting the engine, again ECU thinks engine is stone cold, so gets the plugs to heat up first, hence starting delay.

Totally shocked at the problems a single broken wire can cause!!!!

A common fault aswell from what I can tell.
 

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Super Moderator Technical Supremo Platinum Member
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Yup, coolant temp sensor is common.
And as you say, fools the ECU into thinking the temp is what it isn't.
So runs the engine with wrong mix and can cause all sorts of issues, as you found.

One correction if I may.
The EGR works all the time, revs and load dependent, not temp.
It actually has a cooling function when engine is hot.
 
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