Can a Faulty Coolant Temp Sensor Cause Judder/Lumpy engine 1600-2000 rpm???

**graemer147** · 20-05-2010,10:04 AM

I recently wrote a thread on how my car was very lumpy and juddery between 1600rpm and 2200 rpm. Yesterday i had the car on vagcoms live data which told be after 15 mile motorway driving and 15 mins idling the coolant temp was still only 71 degrees. Diagnosing this as a possible faulty coolant temp sensor i was wondering if this could cause the car to run lumpy/judder at the above revs??? The sender is reading but the temp gauge only goes max to 75ish never does it reach 90 degrees which im now told it should. Could anyone help me on this situation please??? I took the connector off the sender and it changed things but still ran quite lumpy Please help!!!

**Peter D** · 20-05-2010,10:18 AM

you need to actually measure the engine coolant temp as it may in fact not be heating up due to a faulty stat. You could put a peice of cardboard over 75% of the rad and see if the temp goes up to 85/90. If it does then I suspect the stat has failed. Report back and tell up your engine code, it is on the ID label in the Spare wheel bay. Regards Peter

**Sam** · 20-05-2010,10:30 AM

Peter's got you on the way to diagnosing the issues.

To answer the question in the thread title, yes a faulty CTS will cause fluctuating/lumpy idle.

**graemer147** · 20-05-2010,11:16 AM

Hi there, Thanks for the fast reply. The engine idles like a dream no erratic reving etc at all the only problems i get at all are the juddering/lumpiness at 1600-2000rpm. I am getting the temp sensor changed today so hopefully this will solve it other than that i shall meanwhile try and do what peter said and put some cardboard in front of the radiator. I just dont understand the juddering as it is so annoying and im only getting 28mpg is this normal???

**Peter D** · 20-05-2010,11:26 AM

Do you have a multi meter that measures resistance and what is the engine code. Regards Peter

**graemer147** · 20-05-2010,11:44 AM

Hi there peter, Im afraid i dont have a multimeter but i know the engine code is AYM!!!

**Peter D** · 20-05-2010,12:09 PM

I would get a code read while it's in the garage I suspect the EGR valve is the problem. The CTS should read 107 ohms at 90 degrees C. Changing the stat is a major job. Front off, belts off, timing belts off all sorts of stuff. Regards Peter

**graemer147** · 20-05-2010,12:43 PM

Thanks Peter. What is CTS by the way and will vag com (my own) read this???

**Clinterous** · 20-05-2010,12:51 PM

Is the juddering only occurring when you plant the accelerator in 5th gear?
If the temp sender is reading similar to the gauge, then it may more likely be the Stat - which is unlikely to give the juddering symptoms you have.

**graemer147** · 20-05-2010,01:35 PM

Does the stat not cause the heating sysem to blow cool??? As i said the sensor does rise but only to approx 75 degrees it sometimes rises to 80 but then will return to 70 ish even after the longest of drives!! A ful vag com scan produced no fault codes. I should know tonight anyway as it seems to be one of two things the stat or "cts". the cts is being changed tonight so if there is no difference then i will let you know.. Aso it was vagcom that made me realise about the temperature cause i was unsure if it was normal the gauge to be at 70-80 but vag said it should be 85-100 and its running at 70-75.. Cheers Graeme.