igno said:

One more thing, perhaps I've missed it, does the car have an air conditioning?

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Air conditioning was an option on some models, so only you would know if your car has it.

If it does have A/c, it will have the snowflake symbol on one of the control panel buttons, as shown on photos of the 2 available control panels below.
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igno said:

well, the lack of tension of the timing belt is quite unlikely to cause high RPM at idle. But it is always a good idea to replace it & pump every now and again ... What does TPS value read on OBD when this issue is happening? is the battery / generator combo good? When replacing throttle bodies, did you also try new TPS sensor? Could you summarize what was actually tested / done to the car during the whole period?

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Actually, probably you misunderstood me. I don't have high RPM on idle. On my car revs are increasing slightly (about +200 revs) when I'm changing the gear and I'm releasing the gas pedal and pressing down the clutch pedal. In this moment the value of RPMs should be steady for a couple of milliseconds and then the revs should go to the idle value.

OBD couldn't help me because the FiatEcuScan is reading the values once a second, but my issue is happening only for 500 milisecs probably and it is not noticable on the graphs.

Battery and generator are OK. Battery was changed a year ago, generator is showing 14V.

The only thing from my POV which could cause my issue is the throttle block. On my Fiat it is one block with the throttle butterfly, servo motor and TPS. I will try to disassemble my throttle and clean it from the inside.

RE air con - yes, I have it and it is turned off now 'cause of winter

igno said:

Or any other extra electric/mechanic load?

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Hm, only a dashcam connected to the lighter and the CD changer emulator. That's all I have.

Not just a sticking accelerator mechanism? Look at feedback on Multiecuscan. Should be able to do this engine off.

Maigretnz said:

Not just a sticking accelerator mechanism? Look at feedback on Multiecuscan. Should be able to do this engine off.

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If the gas pedal will stick, I will get the same issues on neutral but there are not.

sgorchichko said:

RE air con - yes, I have it and it is turned off now 'cause of winter

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The AC is useful in winter to defog the glass. It acts like a dehumidifier. To clear your glass quickly put AC on and heater. The heater evaporates the water and the AC condenses and removes that water from the car.

Maigretnz said:

The AC is useful in winter to defog the glass. It acts like a dehumidifier. To clear your glass quickly put AC on and heater. The heater evaporates the water and the AC condenses and removes that water from the car.

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Oh yeah, correct. Totally forgot about this lifehack.

I'm still getting the error P1687 periodically. Thinking about the issues with the ECU.