The ECU temperature sensor is a standard bosch resistance - temperature curve.
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| Idle RPM rise when engine hot...normal? http://www.gt4dc.co.uk/forum/viewtopic.php?f=2&t=7091 |
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| Author: | asdrewq [ Thu Jun 12, 2014 5:40 pm ] |
| Post subject: | Idle RPM rise when engine hot...normal? |
I've uncovered what I think may be a problem while driving in all the warmer weather recently: When the car is fully up to temp and i'm driving in stop-start traffic with the AC on, after a few minutes the idle rpm will begin to rise in increments. Gradually it gets higher, the highest it's risen to so far is 2050rpm. Once I get moving again it drops down to normal. If I leave the car idling when stationary at home there are no issues; the RPM stays at 700. Can anyone tell me if this is normal behaviour when the car gets hot? It dosen't seem like it to me. At first i thought it was the classic sign of rad fans not working but I don't think it's actualy overheating - the gauge stays slightly below the mid point and the radiator fans cut in/out as they should. I was thinking it could be the water temperature sensor giving the ECU funny readings but it seems a strange way to manifest if so. One other thing I noticed - when this happens the AC idle-up valve acts 'in reverse' - when the AC engages the RPM drops down a couple of hundred. |
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| Author: | Nibbles [ Thu Jun 12, 2014 11:20 pm ] |
| Post subject: | Re: Idle RPM rise when engine hot...normal? |
The aircon idle up valve is adjustable. Sounds like it may also be sticky. Are you on standard ECU ? |
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| Author: | asdrewq [ Sat Jun 14, 2014 6:21 pm ] |
| Post subject: | Re: Idle RPM rise when engine hot...normal? |
Yes standard ECU. I checked the idle up valve using the much revered 'blowing through it with a hosepipe while clicking it on and off' approach and it is fine. I also freed up and cleaned out the ISCV not long back so don't think it's that. I'm sure it's the ECU doing it as the step changes in RPM were very accurate of the manner of 800, 900, 1000, 1050, 1350, 1500 etc (I have a digital rpm gauge) and idle stays high with the AC VSV off, just can't yet think of a logical cause... Think i'll try testing the engine temp sensor, and maybe take a look at the engine and AC ECU PCB's for any leaky caps as i've heard that can be a problem on jap cars of this vintage. |
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| Author: | NNZ [ Tue Mar 17, 2015 9:10 am ] |
| Post subject: | Re: Idle RPM rise when engine hot...normal? |
It's old topic, but maybe you got any information. I too have wrong data from water temperature sensor |
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| Author: | Nibbles [ Wed Mar 18, 2015 11:08 pm ] |
| Post subject: | Re: Idle RPM rise when engine hot...normal? |
The ECU temperature sensor is a standard bosch resistance - temperature curve.
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| Author: | asdrewq [ Thu Mar 19, 2015 10:40 pm ] |
| Post subject: | Re: Idle RPM rise when engine hot...normal? |
I never did get to the bottom of this, I did figure out it has nothing to do with the AC though. Stationary for more than 2 minutes in stop/start traffic and the revs rise all the time now. |
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| Author: | NNZ [ Wed May 27, 2015 6:46 pm ] |
| Post subject: | Re: Idle RPM rise when engine hot...normal? |
My problem was, that water temperature sensor always show -15 degree of real temperature. I've changed 4 of them, but nothing. So we installed a resistor and now it's perfect |
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