Lumpy idle?

[Papa Lazarou]

Well, maybe not that lumpy. Just sort of uneven really. The car burbles away at idle and sounds quite powerful (I liken it to a TVR type sound). I'm just getting used to the car having actually been driving it for only a couple of weeks now.

Does anyone else have this? What can cause it? I'm not concerned really, just wondering if its a :) A normal feature of the car or b :) something needs looking at.

Hopefully nowt major if b :) as the motors done only 40K and appears to have complete FSH (although I can't read Japanese unfortunately)..

Any opinions or guesses at this welcome.

Thanks

[This message has been edited by Papa Lazarou (edited 14-09-2001).]

[SteveCarter200]

Just a guess, seeing as I own an S13 but do S14s have the AAC valve thingy? Dirty valves have been a cause of uneven idle on plenty of S13s. Or possibly a dirty AFM.

Steve

[geoff_s14]

As standard, the s14 should idle smoothly and unobtrusively. If you find out what's making yours sound like a TVR let me know - I'd wouldn't mind some of that. http://300zx.co.uk/200sx/ubb/smile.gif http://300zx.co.uk/200sx/ubb/smile.gif

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Geoff
Emerald S14, heavily modified by shopping trolleys.
http://www.animfactory.com/animations/transportation/cars/mirror_md_clr.gif
http://www.mpz.co.uk/cwm/ups/kamikaze/smilie_groupflip2.gif

[Tom_S14]

Geoff, a honking great 5l V8 !
S14 does have an AAC valve thingy, kind of an auxillary air bleed device.
Wonder if an ECU fault check would throw this up if it was faulty ?
Does this uneven idle happen when the engine's warmed up too, or just cold ? The AAC valve thingy on mine is set quite high on startup, and settles down to a lower value after a bit (so that expensive gadget on my dashboard was useful for something at alast http://300zx.co.uk/200sx/ubb/smile.gif )

Tom

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1996 Blue/Green S14 (manual)
K&N cone filter
2.5" Tube-torque Cat Back Exhaust.
TechTom MDM-100
Race-Technology AP-22
http://tom.marshall.tripod.com

[Papa Lazarou]

What does this valve actually do? I noticed when its idling the engine makes a definate clunk every so often and the engine revs rise (about 1200), then another "clunk" and the revs drop back to 800-ish a few seconds later. Or is that just the cooling fan activating?

Hmm.. So the S14 is supposed to be very quiet and everything at idle then. Like I said, this one "burbles" and also the bonnet vibrates (you really notice this when water is on the bonnet - you see all the droplets moving around).

The idle seems a little more uneven when cold, thinking about it.

[Tom_S14]

As far as I can make out from the diagram, the valve opens up a bypass round the throttle plate. It acts a bit like a choke on a carb, in that you need more throttle opening when the engine is cold. On a carb this is done mechanically by limitting the throttle stop position. With this valve, extra fuel/air is metered in by just bypassing the throttle altogether.
This is why I was wondering whether it still does it when the engine is hot.

The only noise I've heard up on the S14 is timing chain rattle caused by a worn chain tensioner.
Hunting revs can sometimes be caused by a leaking hose somewhere on the inlet, might be worth just having a look to see all the pipes are in good condition, no splits, nothing falling off ! But with 40k miles I'd be suprised.

Only other thing I can think of (your car is an import right ?) is that maybe the timing is set a bit off, perhaps it's set for higher octane japanese fuel. This could cause slightly lumpy idle I reckon... (maybe)

Tom

[Rossy]

Yo Papa,

I know the Clunking noise you mean...I've had it on mine since I bought it - I'm sure its the fan...

As for the lumpy idle.....er...dont have a clue.

I'll get my coat.

[geoff_s14]

Jon,

The fan is on a viscous coupling, so won't kick in and out suddenly like conventional electric fans do.


That clunk you describe sounds exactly like the noise I hear when the AC compressor kicks in, and is either the compressor itself, or the fast idle valve activating. This valve responds to a drop in the idle speed below a certain threshold. It clicks in to increase the intake airflow, which raises the revs at tickover. Its there primarily to compensate for the decrease in idle speed which results when the AC compressor kicks, to save the engine from stalling.

It sounds like what's happening in your case is that because idling is lumpy, the revs are falling below the threshold for fast valve idle activation. When the latter kicks in, the revs pick up, surge beyond the cut off threshold for the valve, which then kicks out, causing the revs to fall back down. I had exactly this problem on my old Scirocco which had an idle that surged in a cycle between 600 and 1100rpm. Although I never found the exact cause of the problem, I cured it by cranking up the idle speed a bit.

It could be that the fast idle valve on the 200 is one in the same as the auxilliary air valve Tom was describing, since both perform a similar job, but I'm pretty sure that in the scirroco the AAV was a seperate unit.

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Geoff
Emerald S14, heavily modified by shopping trolleys.
http://www.animfactory.com/animations/transportation/cars/mirror_md_clr.gif
http://www.mpz.co.uk/cwm/ups/kamikaze/smilie_groupflip2.gif

[Daniel san]

Mine used to do that, as I'm sure Matt_s, Steve Carter and Ben Taylor will tell you. Hasn't done it since it's re-build but I'm sorry I can't say why cos I dunno.

So I'm no help at all. Sorry

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Dan
www.puresx.co.uk

'98 Saphire Blue S14 (manual of course)
Far too many mods to list here, it takes up far too much space and after being asked very nicely I've decided to shorten the sig (Is that a WOOHOO I hear??)
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Do not take offence to anything I say, even though I probably mean it. I am more than slightly mad, so just chill de feck oooot, ok!

[Papa Lazarou]

Thanks for all your responses. Theres a few things I think I'll check now. At the end of the day its not bothering me much, or cutting out or anything so I guess I'll put up with it if I can't fix it.

Just wondering if it could be anything to do with the electrics? The battery has been a bit low recently - could that cause it?