Rising tick-over
Q I promised my stepfather I’d ask you about a new problem on his 2007 SEAT Altea XL 1.9 TDI. I’ve attached a photographic image of the sticker inside his service book with all the details. A couple of weeks ago Geoff (my stepfather) asked my opinion on the fact that his SEAT (which he has owned for many years) had suddenly begun to raise its tick-over speed from around 800rpm to just over 1000rpm when it was stood in traffic for about a minute or so. Apart from that, he said it was behaving as normal with no dashboard warning lights.
Last weekend I took along my new Foxwell diagnostic tool, which I’m still learning about. There were no stored engine codes in the SEAT, and we got a green ‘tick’ LED on the front of the tool. So, with the engine idling, I tried looking at live data, not really knowing what to look for! I’d looked a little on SEAT forums or VAG forums beforehand, found people with similar problems, and favourite suggestions were a faulty coolant temperature sensor and a low battery. Geoff’s battery is fairly new, he tells me.
The car was behaving perfectly at idle, after being started up from standing a while, so Geoff took it for a drive with me as passenger. We didn’t do live data while driving. I assume ECT (C) on my OBD tool screen means coolant temperature. It read 37°C before we started the drive.
We did a few uneventful miles then returned to my parent’s home and parked in front of the garage, leaving the motor running. I connected up the OBD tool again and went to live data. The ECT (C) reading was 77°C, but the dashboard temperature gauge was reading normal at 90°C. The engine tick-over on the OBD tool was about 830rpm.
Then after between about 60 and 90 seconds, the tick-over speed suddenly rose spontaneously, but also heard the electric fan kick in. Geoff had never noticed this. We raised the bonnet, and the fan was running. But it did cut-out again after about one minute, but the engine revs remained high. On my OBD tool, the ECT (C) readout was still about the same (78°C), with the engine revs at 1040rpm.
Geoff told me if he were to drive off the revs would be normal the next time he pulled up, but then after a minute or so would rise again. All I did was turn off the ignition and restart the engine, and immediately the revs settled back to around 830rpm. That’s as far as we took things.
I’m guessing the coolant temperature sensor may still be a favourite to blame for this glitch, though the radiator fan kicking in at the same time as the engine tick-over speed picked up, when the car hadn’t been stood for more than two minutes, in cool weather, and had been constantly moving while driven, is an aspect I feel might be connected, but I’m not sure what it means.
Your thoughts will be gratefully received. Mick Dean A
I would certainly connect the cooling fan coming in, and the engine tick-over speed rising, these two actions may be due to the coolant temperature sensor. Although the ECT reading on your scanner is showing 78°C, the information I have from Autodata informs me that the vehicle should have a second coolant temperature sensor which is located on the radiator.
This sensor is also connected to the ECU and would operate the cooling fan, the rise in idle speed would be to compensate for the extra load on the system from the cooling fan.
Autodata does also inform me that there was a known problem on this range of vehicles with the throttle pedal sensor, but I do not believe this is applicable in this case and I would first check the radiator coolant sensor.