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Idle when warm

tribalscribble

tribalscribble

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Location
Glasgow
Car
2004 i-vtec sport
2004 i-VTEC sport 2.0 Petrol

When the car is warm, and say sitting in traffic or at a junction. The revs seem to drop from normal, to around 500-600rpm as if something is laboring the engine. If i move the steering wheel or turn on the aircon (or anything power hungry) the engine revs back up to regular idle speed for a few seconds, then falls back to 500-600rpm. On a couple of occassions, the fan has turned on and almost stalled the engine, but the rev's bounced back up (i ***ume some sort of anti stall on the ecu). Sometime it's fine and doesn't have the issue, but more often than not, it is present.

The battery is about a year old, it starts strongly, so I would be surprised if it was the battery. I'm a little suspicious of the alternator or the power steering pump (or whatever else is on the aux belt) as there was a pronounced whining noise coming from the engine a month or so before this happened. The garage couldn't hear it, but given I've owned the car for 6 years, I know it's noises and it was definitely a new one.

Does this make sense to anyone?
 
Is the IACV working ok?
 
Sounds like your AC compressor is kicking in. Is your climate set to AUTO?
 
My first check wpuld be the Idle control valve being slighly dirty, they normally just need taking off and cleaning. However it can be other things too including the MAF sensor or even the lambda sensor.
 
Thanks guys. I think the IACV is a good shout, as there seems to be no other issue when driving etc. It's purely at idle. Looks like it's a big fiddly to get in at the IACV. Might get me local wee garage to sort it out.
 
Was a nice night so decided to get the bonnet up and have a poke about. Found that the screw clamp that holds the big black air pipe onto the throttle body was completely loose to the point I could spin it around. Gave it some wd40 and a good tighten up. Seems to improved the idle problem so that its idling almost constantly at about 700-750 when warm much smoother idle too. True test will be rush hour tomorrow. Thats where I notice it most.

***uming when the engine heats up the pipe expands a bit and leaks air in if its not clamped.
 
Took it to the local garage. Appears to be the alternator is dying and when there is any sort of decent load such as radiator fans or a/c it isnt putting out enough juice. 110k miles old so cant complain
 
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