|
Post by wannabe on Nov 11, 2016 13:10:19 GMT
Excellent. Just as I need it to work perfectly as I start a 100 miles a day commute, it starts being weird Issue is as follows: Start up from stone cold and just let it idle, revs are higher initially (as would be expected) but then settle back down to 1k as it warms up. All is good. However... Drive off and drive around in it, the engine up to temperature, and when you come to a stop the revs are sitting at 1250-1400rpm at 'idle' and don't seem to show any sign of dropping, even after being left for a while I'm not even sure where to start - it's a mechanical throttle cable so I don't think it is anything getting stuck or snagged (but will have to check) but if it's not that, what else could it be?!? Some sort of air leak in some tubing meaning it thinks it is running lean and increasing the idle/fuelling? I can't think it would be damp on any connections because it would do it all the time, surely? And it can't be a sticky choke (however it is done on the 5s ) as that would also mean it did it all the time? Any and all suggestions gratefully received!!
|
|
|
Post by myothercarsa2cv on Nov 11, 2016 14:16:57 GMT
Could be idle control valve on the blink? Remove the hose and put your hand over the inlet, if the idle settles you've found your problem (in theory).
|
|
|
Post by joeytalent on Nov 11, 2016 16:58:59 GMT
Higher idle = MOAR AIR from somewhere.
Because it happens when it warms up, the Idle Speed Control Valve (ISCV) is probably a good place to start. Off the top of my head, there's just two bolts that hold it on to the side of the throttle body. You should be able to get if off pretty easily, and clean it out with throttle cleaner. Inspect the gasket as well.
Another to check for would be airleaks. With the can of throttle body cleaner, or carb cleaner, or even WD40, spray on all the air hose joins with the engine running. If you get a dip in the engine speed, you've found a leak.
Finally, it might be worth cleaning the throttle body out as well. The butterfly valve in mine actually wore unevenly and it was no longer a perfect circle - which caused a higher idle.
|
|
|
Post by wannabe on Nov 11, 2016 19:58:06 GMT
Oooh, excellent detective work - thanks for the suggestions, I'll try to get onto those this weekend!
It better not rain...
|
|
|
Post by Woofwoof on Nov 11, 2016 22:34:48 GMT
Five minutes to remove the T/B, so that's something.
|
|
|
Post by wannabe on Nov 13, 2016 0:17:55 GMT
Right, well, it's rained all day and when I had a look it was dark and I couldn't find a torch and I didn't want my hands to get dragged into any moving parts like a muppet... What I'm basically saying is I need to read up on what I'm doing before I do anything - and in the meantime, swap with the missus for my new ridiculous commute for a while! I fail at mechanics lol EDIT: I found this - looks useful but I've not had a chance to read it all yet: www.miata.net/garage/isc.html
|
|
|
Post by wannabe on Nov 13, 2016 0:28:14 GMT
Oh, and I forget to ask - if there is an air leak, am I correct in thinking it will be making it run lean?
And it's therefore a bad idea to really give it any revs / sustained runs?
|
|
|
Post by Woofwoof on Nov 13, 2016 1:39:44 GMT
A minor air leak that affects idle speed won't really affect fuel mixture while driving. Sure, it will make the engine run a little lean but that's about it, a little extra air from a vacuum leak would have a negligible effect bar upsetting engine idle.
|
|
|
Post by martiny on Nov 25, 2016 13:29:07 GMT
A minor air leak will raise the idle speed but the car won't run lean because the ECU will correct the mixture using readings from the O2 sensor.
I take it this is a Mk.1 1.6, in which case you have two valves controlling idle air - the one bolted to the side of the manifold is a thermal valve (wax valve) for cold starts and should close up as the car warms up, the other one, the ISCV, is underneath the throttle and is driven by a solenoid controlled by the ECU to correct idle speed. Those can get a bit gummed up and stick open but carb cleaner frees them off (at least it works a treat in the Mk.1 1.8 version - never tried a 1.6).
Hope that's useful.
|
|