Thread: What are the signs of a faulty coolant temperature sensor?

My car for a while has been ticking over rough on idle but only when the temperature reads 90', it starts first time every time in an instant, but once it warms up to temperature the engine starts to shake and miss fire.

It also takes around 15 miles or 30 mins or so to properly warm up (on the cluster i mean, the heating is warm long before the cluster reads 90')

This morning whilst queuing down the M606 for about 5 mins stood still the engine temperature began to drop, bear in mind the car had been running a good 35 mins and covered around 14 miles to this point, surely being stood still for less than 5 minutes would not cause the cluster temperature read out to drop 1/4 of the way back down?

The car drives perfect and gives back good MPG and miles to the tank however on idle it's a pig when warm NOT when cold.

Can anyone shed any light?

whats it showing on the gauge and if you have the oil temp on the DIS whats that at,coudl possibly be a stuck thermostat

Don't know what the oil temperature is, i could check that on the DIS on the way home tonight.

When the car eventually warms up, it shows 90' but once sat in traffic the gauge then drops as it did this morning.

The lumpy idle is doing my head in!

is there not someone up your way with vag-com or similar

Been scanned and there are no faults, would a nackered DMF cause the car to miss fire? Or would it just give a lumpy idle, the engine misses, well the engine sounds like it's missing, lift the bonnet and it's shaking its tits off, feather the gas pedel slightly and the rough idle goes away, the car drives perfect and when it's cold it idles perfect.

could be air flow meter,coil/s or plug/s,injector/s etc but i cant see how that will relate to engine coolant temp

I thought if the coolant temperature sensor was nacked it would over fuel the car on idle thus causing it to idle like a crock of sticky stuff? Is this completely wrong then?

could possibly,i have no experience with the coolant sensor though so cant help there,im sure it would show up on vag com though

Aiden - I will re-scan it for you if you want. However, you could always take it to my man in Leeds who will diagnose immediately !

Originally Posted by mike foster

Aiden - I will re-scan it for you if you want. However, you could always take it to my man in Leeds who will diagnose immediately !

Thanks Mike, I might need you to do that for me. Who's your guy in Leeds you know? Is he a Audi specialist?

dont think scanning will show it if the sensor is within its perimeters,had this issue with an air flow meter,its was knackered but still sending a signal, unfortunately the wrong signal so the fuelling was all over the place but the ecu saw a signal and adjusted the fuelling and timing to suit without throwing a code or light

Originally Posted by marknjayne

dont think scanning will show it if the sensor is within its perimeters,had this issue with an air flow meter,its was knackered but still sending a signal, unfortunately the wrong signal so the fuelling was all over the place but the ecu saw a signal and adjusted the fuelling and timing to suit without throwing a code or light

What was your car doing to make you think it was the air mass meter mark?

Thanks for your help.

Volksworks.com - the owner has 30 years experience with VW and is hands on. Does all the work for taxi drivers in Leeds and BKD engines are bread and butter ! VAT registered and sorted my turbo with Warranty Direct ! PM me for a scan if you want one.

Thanks for that Mike!

Driving the car for 27 minutes and covered almost 12 mile, the car still hadn't warmed up on the gauge, the heaters themselves in the cabin were blasting out 27' worth of hot air.







Does this look right?

Seen this thread this morning and tracked mine on the way to work this morning.

Mine was pretty much fully warmed up by 8 minutes & 4.5 miles.

Hi matey, do petrol engines warm up quicker than diesels? I don't know, i don't even know if this is abnormal or not. All i know is, the missing on idle is royally pissing me off.

I've no idea unfortunately mate

Hope you get it sorted soon!

Originally Posted by AidenUK

Hi matey, do petrol engines warm up quicker than diesels? I don't know, i don't even know if this is abnormal or not. All i know is, the missing on idle is royally pissing me off.

Yes petrol engines warm up a damn sight quicker than diesels.

I have a 53 plate 2.0TDI and it is doing the exact same thing, no movement on the temp gauge for what seems like ages and then goes straight to 90 degrees... also have the lumpy idle when warm.

Seems to be quite a common thing but I'm unable to find a definitive answer anywhere on how to solve it!?

Is yours missing on idle from time to time, i can feel the vibration through the gear stick, i watch the gear stick and see it shake and move when the car is at it's worst!!

Originally Posted by AidenUK

Is yours missing on idle from time to time, i can feel the vibration through the gear stick, i watch the gear stick and see it shake and move when the car is at it's worst!!

I wouldn't say it was actually missing but it does get very lumpy, it also hunts at times and the revs will pick up to just over 1k, sit there for a few seconds and return to be being lumpy... I've only noticed it the last couple of days so not had chance to investigate it properly as yet. The confusing thing is how is this and the temp gauge's weird behaviour linked or are the two seperate problems??

Mine also has lumpy idle and also would like to know, ive been told it could be my EGR valve and may need replacing?

I'm fecked if i know.

If i pop the bonnet the engine is rocking away, you can feel the shakes and judder in the car, you can watch the gear stick shake whilst in gear with my foot pressed on the clutch, the rev counter doesn't fluctuate up or down at all.Properly pisssing me off if I'm honest, the car has been scanned countless times and no faults are thrown up, i've whacked countless amounts of injector cleaner through it and it had 84 quids worth v-power diesel the other day and still not a turds worth of difference.

Thermostat for sure, and it won't show on any scans. Does the temp gauge drop of colder if your coasting down a hill? I had a similar fault on my old 1.8T Golf, it ran like a new car once the thermostat was fixed and the ecu gets all confused from the false readings from related sensors...

No the thermostat doesn't do that matey.