coolant temp sensor; different reading from ecu and cluster?

[tmh983]

I noticed on my VCDS scanner the other day that the ECU coolant temp value in block 003 was only getting up to around ~65° max, but the Cluster coolant temp is showing 90°+ at the same time....?
Are they separate coolant sensors or does the cluster/ecu share the same sensor?
Any other reason they would not be reading the same temp?

[Lito]

Same sensor but seperate signals. If you get a new one make sure it's a genuine green top one.

[tmh983]

ok cheers.
I've been noticing that its been slightly idling high (1100rpm-ish) and then gradually reducing to normal (like when I stop at a set of lights). When I look at the idle stabilising block in VCDS it is applying anywhere up to -10% to the idle speed controller to bring the speed down to normal (not sure if this is an excessively high amount of correction or not). Have been crawling over this thing trying to find the reason for it, but so far havn't been able to find the cause (looked at afm, coils, map sensor, throttle body etc). I'm think this may be the root cause of all this problem, if the ecu thinks the engine has not yet fully warmed up, it may be using a slightly higher base throttle angle setpoint for the throttle angle, then the controller slowly regulates it down to the target speed... sounds plausable?

[The One]

ok cheers.
I've been noticing that its been slightly idling high (1100rpm-ish) and then gradually reducing to normal (like when I stop at a set of lights). When I look at the idle stabilising block in VCDS it is applying anywhere up to -10% to the idle speed controller to bring the speed down to normal (not sure if this is an excessively high amount of correction or not). Have been crawling over this thing trying to find the reason for it, but so far havn't been able to find the cause (looked at afm, coils, map sensor, throttle body etc). I'm think this may be the root cause of all this problem, if the ecu thinks the engine has not yet fully warmed up, it may be using a slightly higher base throttle angle setpoint for the throttle angle, then the controller slowly regulates it down to the target speed... sounds plausable?

Have seen some older beetles do this, soloution: Replace sensor.

So yes, plausible. As previously mentioned, ensure it is green.

[vdubmotorworx]

Black coolant sensors are rare now as most have been replaced already. But if a bettle / golf 4 / bora has running issues and there is a black coolant sensor then first job is to change it for a green one....VDUB..

[tmh983]

just put the new sensor in and idle problems are solved (finally, hurray!)
The old Black sensor that came out looked like the outer brass coating had mostly corroded away, it looked like it was pretty bad shape.

On VCDS now the idle regulation sits around -2% which is pretty good i think. The idle feels smoother (although that could just be a bit of placebo effect...), but what is most noticeable is that the throttle response just off idle it is MUCH smoother. It is heaps easier to drive the car smoothly, especially at low speed. Will also expect to see a slight improvement in fuel economy too i think.

P.S. anyone else with an old style black sensor, i would recommend changing it for a green one, even if you don't think there is any negative symptoms with you current sensor. Changing the sensor is probably the easiest thing i have ever done on an engine, it cost me about $30 for the genuine sensor, and literally about 30sec to change out, its almost like VW new this sensor was going to be problematic, so they designed it to be as easy to change as possible...

[vdubmotorworx]