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Jul 20, 2011 15:36:00 GMT
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My car's got a rough idle problem which usually occurs when it has warmed up but can also happen starting from cold. But sometimes I can drive for miles and miles with no problems at all!
Its been getting worse over the last 6 months or so, to the point where now it sometimes cuts out when coming to a stop and struggles to start at all unless I press the accelerator pedal at the same time as turning the key.
Its a 1991 Mk3 Fiesta 1.4i CFI CVH, if that helps.
any ideas?
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1994 Mazda 323f 1.6i 16v GLX
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no help?  got my MOT in just over a week, bit worried that its gonna fail on this so need to sort it asap! |
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1994 Mazda 323f 1.6i 16v GLX
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I'm not particularly familiar with the setup on that engine.
I think if it's not a problem that's there all the time then you can probably rule out a mechanical defect in the engine assembly.
More likely it is going to be related to the engine control system.
The only thing I can think of which I've seen before which was anywhere near similar was failing ignition leads on a Ford KA.
On the KA the ignition leads are really long and they go to a coil which is mounted on the back of the engine.
If the slightly earlier Fiesta is using the same setup then that might be a good place to look.
It sounded like very similar symptoms to what you're describing. Could happen anywhere at any time and just caused a bit of rough running which you could work-around if you were more determined in driving style.
Either way, looking at ignition as a cause of rough running at idle isn't a bad thing to do. But careful not to go to the expense of changing perfectly good spark plugs. So many people do that and it's pointless.
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Jul 21, 2011 10:29:58 GMT
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Thanks for the reply,
I tested the leads when it was running rough last week and they all had spark. I will have to wait for a day when the problem returns so I can test the plugs.
Could it be the MAF sensor?
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1994 Mazda 323f 1.6i 16v GLX
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Jul 21, 2011 11:26:23 GMT
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It sounds like the usual idle air valve trouble to me...
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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Jul 21, 2011 11:41:54 GMT
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is that the part which 'flips' open and closed inside the airbox?
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1994 Mazda 323f 1.6i 16v GLX
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Jul 21, 2011 12:01:05 GMT
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no, it's a control valve within the injection system (sometimes separate, but I think on the fiesta it is part of the CFI unit). It regulates the flow of air past the throttle plate, and hence controls the idle. When it starts to stick, you get all sorts of idle issues - sometimes high tickover (stuck open) or no tickover (stuck shut) or fluttering and erratic idle (sticky valve not working quickly enough, ecu tries to "catch" the stall, overdoes it, revs go up, ecu tries to stabilize again.... etc)
I'll have a look and see if it's replaceable on the CFI, and let you know later.
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To get a standard A40 this low, you'd have to dig a hole to put it in |
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Jul 21, 2011 12:19:36 GMT
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Fantastic, definitely sounds like that part is the culprit from how you described it.
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1994 Mazda 323f 1.6i 16v GLX
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Jul 22, 2011 21:04:36 GMT
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You can clean them out with carb cleaner (better than thinners). Vauxhalls have had this problem for 20 years and this is the best way of doing it.  It's just clogged with breather pipe oil (through the inlet) and it hardens and thickens. I passed my MOT on the MGF a few months ago with throttle cable sticking at 3000rpm! |
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Last Edit: Jul 22, 2011 21:05:08 GMT by DavidB
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Jul 23, 2011 10:06:07 GMT
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I have been searching my engine bay for the part, any ideas where it should be situated? Hopefully a clean up should fix her |
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1994 Mazda 323f 1.6i 16v GLX
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Jul 27, 2011 22:40:13 GMT
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no help ? anyone know what an Idle Speed Control Valve looks like and where they are usually situated in an engine bay? |
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1994 Mazda 323f 1.6i 16v GLX
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It's a simple one way valve, ie air in, air out. You'll either have is integrated in the inlet manifold or a separate valve that has two pipes, one from the plenum and the other into the inlet. It bypasses the throttle valve to keep the vacuum up in inlet so the engine keeps turning over. Here's what the CVH unit looks like:  Stick your hand under the inlet to have a fish round for it - rubber pipe and a wiring plug. Watch you don't touch the starter motor.  |
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sweet, thanks mate il have a look.
if it is integrated into the inlet manifold is it possible to clean it using carb cleaner still?
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1994 Mazda 323f 1.6i 16v GLX
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Tim
Posted a lot
Posts: 3,340
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First thing i'd try is dumping a lod of carb cleaner into the throttle body (on and off throttle)
worked wonders for my bad idle...
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Jul 28, 2011 10:16:22 GMT
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Yeah, as 'intergrated', it'll be bolted in (and not like the Vauxhall ones which are literally suspended in mid air with pipes).
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It's just clogged with breather pipe oil (through the inlet) and it hardens and thickens.
