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Weird Idle problem

Posted: Tue Dec 24, 2013 7:37 am
by CARRisma
This issue has occurred twice within a week or so.

The engine wasn't stone cold, but had been left parked for about an hour and a half. So was cold but not stone cold as if left over night. When I started the engine, the revs went up to about 2000 RPM, higher than usual and stayed there for about two or three seconds. This is out of character. Then the revs dropped to about 1200, then up to about 1800, down to 1200, up to 1800, down to 1200, up to 1800 before settling at a constant idle of about 800-900. It paused at each level (1800 / 1200) for about a second each time. The up and down revs seemed very controlled, so not sure if I would describe it as erratic.

Currently my car is suffering from a very small coolant leak. I think leak might be too strong a term to describe the seepage from the coolant pipe directly below the distributor. It started about a month or two ago and has only lost less than 1 inch worth of coolant from the reservoir bottle (which I've obviously topped up). I'm getting this sorted next month at PAW when they are gonna fully poly bush my car :) I point this out because when I carried out a coolant change about a year and a half ago, the coolant level dropped at one point, maybe when the thermostat opened or something? And when that happened, the revs acted peculiarly. From memory, it was like what has happened recently. To those of you who have ran the engine without the PCV tube connected, it's a bit like that, but with seemingly controlled pauses at the max and min RPM. So, I'm wondering if the cause could be air in the coolant system due to the leak / seepage?

@honda-hardy, you've fiddled with the FITV. Do my described symptoms match what you've experienced?

Posted: Tue Dec 24, 2013 10:00 am
by Merlin
If you have a coolant leak I bet that is the source of this problem. It may be affecting the FITV and IACV, both help control idle through contact with the coolant. You probably have air in the coolant.

Re: Weird Idle problem

Posted: Tue Dec 24, 2013 11:33 am
by CARRisma
That's what I'm hoping!

Posted: Tue Dec 24, 2013 1:53 pm
by honda-hardy
your symptoms definitely sound like air in the coolant.