2.0 CT Engine Hot Idle Issues

[Dommo]

Hi all

I've taken my Activa out for a spin this morning, and something that has always plagued this car since I bought it a few years ago is the engine idles very poorly when it is started while up to temperature.

When started from cold, it idles perfectly. When running and slowing down to a junction, it idles perfectly. When I turn the car off at operating temperature, and come back to it within a few minutes, it will idle very badly, as though it is trying to stall then save itself, then stall and saves itself. After driving it for a few minutes it will idle again perfectly fine. I'm not sure if there is a certain amount of time between it hunting for an idle and it being able to idle, as it's not my daily driver.. So I don't know when it comes and goes.

Sounds like a bad temperature sensor somewhere to me, but the gauge on the dash works perfectly. Does the engine ECU have a different temp sensor?


Thanks for any help, Dom.

[white exec]

Yes it does.
Two, or even three, temp sensors on the water outlet:
- gauge (referred to as Dial on many circuit diagrams)
- injection ECU*
- cooling fan(s) control*
* rolled into one on later cars.

[davoxx]

I had an issue with a rough warm idle on the TCT that was the coil pack. Just an idea.

[Dommo]

Yes it does.
Two, or even three, temp sensors on the water outlet:
- gauge (referred to as Dial on many circuit diagrams)
- injection ECU*
- cooling fan(s) control*
* rolled into one on later cars.

Thank you for that. I’ve just taken a look on service box and found the following sensors:

So as I have air conditioning (which works!!) I would imagine I have the two sensors labelled 1338 34 and 1338 56. I wonder whether my blue sensor is the problematic one?



Thanks for the suggestion on the coil pack, I did actually change my coil pack and the igniter (I think that’s what it’s called anyway, a little flat plate device mounted to the chassis with thermal compound for heat dissipation) just as a matter of course. I might try and refit my old coil pack if the temperature sensor comes back as working, so thank you again for the suggestion.

[white exec]

The temp sensors on our engines are usually colour coded for function:
BLUE - thermistor (viariable resistance) for the Gauge
GREEN - temp info for injection ECU
BROWN (marron, or even maroon on some parts lists!) - water temperature control unit (WTCU) where fitted, contntrolling the radiator fan(s).

It's the last two that can get rolled into one, where the Injection ECU also controls engine cooling.

[Dommo]

Typically the sensors are very hard to reach.. Doh! I was considering disconnecting them to see which exactly does the gauge and which does the ECU. Presumably if the ECU one is faulty, removing it either won't make any difference (if it is open circuit), or it will make a difference (if it's reading one set value).

I've found an OE blue sensor for £15, and unfortunately for the maroon sensor I can only find non OE, on ebay at least:
https://www.ebay.co.uk/itm/362502896369 ... SwVCpcCOdg

It's part number on the advert title is different, but the list of part numbers in the description cover the one I need. I can't tell whether it's the right one though, maroon, brown, who knows!