Discussion
Hi All,
I’ve a MK1 MX5 that upon starting has a bit of a bad idle and it rises and drops to about 400rpm and usually cuts out. If I hold some high revs for 30 secs it’ll sometimes settle around 950 rpm where it should.
Once the revs are settled at 950 rpm and I depress the clutch it’s still at 950rpm. If I select a gear with the clutch still depressed it drops to around 400rpm again and will cut out if no throttle input is made.
I’m aware of bridging the connections and setting the base idle so the mechanical idle matches the ecu settings (assuming they don’t match at the moment) I think that’ll solve the poor idle upon starting (link to technique below)
https://www.miata.net/garage/KnowYourCar/S7_Idle.h...
I know the car has a clutch switch under the clutch pedal and neutral switch on the gearbox in the same circuit. Based on the below I’m wondering is selecting a gear ‘ungrounding’ that connection and sorting the base idle will resolve it? If it was that wouldn’t that mean it should also drop rpm and stutter when the clutch is depressed?
From this thread https://www.pistonheads.com/gassing/topic.asp?t=98...
‘Murray1986’ says the below.
I’ve a MK1 MX5 that upon starting has a bit of a bad idle and it rises and drops to about 400rpm and usually cuts out. If I hold some high revs for 30 secs it’ll sometimes settle around 950 rpm where it should.
Once the revs are settled at 950 rpm and I depress the clutch it’s still at 950rpm. If I select a gear with the clutch still depressed it drops to around 400rpm again and will cut out if no throttle input is made.
I’m aware of bridging the connections and setting the base idle so the mechanical idle matches the ecu settings (assuming they don’t match at the moment) I think that’ll solve the poor idle upon starting (link to technique below)
https://www.miata.net/garage/KnowYourCar/S7_Idle.h...
I know the car has a clutch switch under the clutch pedal and neutral switch on the gearbox in the same circuit. Based on the below I’m wondering is selecting a gear ‘ungrounding’ that connection and sorting the base idle will resolve it? If it was that wouldn’t that mean it should also drop rpm and stutter when the clutch is depressed?
From this thread https://www.pistonheads.com/gassing/topic.asp?t=98...
‘Murray1986’ says the below.
Murray1986 said:
I'd be taking the clutch switch apart as thats what happened to mine and I compensated by adjusting the idle speed, seemed to do it more after a hot restart which was odd.
Basically there is a neutral switch attached to the gearbox that when you shift to neutral it grounds a circuit to the ecu telling it maintain the engine idle speed / inject fuel etc
the other one that does this is the clutch switch (uses the same circuit if I remember right) when the clutch pedal is up the circuit is broken and ecu can see the car is running normally driving along and it won't attempt to correct the idle when you push the pedal down the switch is activated and it grounds the same circuit as the neutral switch and this tells the ecu, ok i need to maintain the idle speed now and inject fuel as apparently when you lift the throttle above certain speeds (over-run) the ecu stops injecting fuel which you would probably do when coming up to a junction, unless at Mcdonalds.
Thats why it stalls as the ecu just sits there drinking tea because it thinks the momentum of the drivetrain? will keep it running but when you clutch down you've knackered that idea!
So to fix it all you do is unplug the connector in the footwell going into the switch, use a 17mm spanner i think it is to undo the nut, twist the switch anti clockwise to remove it (its threaded into its bracket and the nut locks it into place) once its out get a small flat blade screwdriver and prise the metal tabs that hold the switch together until the swtich comes apart, then remove broken spring, clean any contacts that look crap and replace the spring with a clicky pen spring! nice and cheap! then bend the tabs down again and refit! i tried to align mine so that the switch was fully pressed and depressed when the pedal was up and down, you'll know what I mean one you see the little rubber pad the pedal contacts or just remember where yours was before you take it out.
That should hopefully solve it! Although I haven't actually tried driving mine again yet as I'm fixing other things but I'll let you know when I do unless you do try it first. its all over miata.net and other 5 forums anyway.
don't buy the clucth switch from autolink part n.o B001 or whatever it is, its the damn brake light switch! (think it might be a clutch switch in the bongo) I think its LA01 you want if you can't be bothered taking it apart and finding a spring from a pen
The neutral switch rarely fails from what I read and its easy to test as I remeber when out in mine I would shift to neutral when coming to a stop to stop the revs dropping or sometimes even stalling under hard braking! Only realised that after I bought one though and saw it was a bit of a pig to replace and thought sod it!
There is also a way to test it with an LED light in the diagonstic box on early 5's from what I've read, by placing it between MEN and GND i think it is and then when you press the clutch or put it in neutral the LED should light up showing the switch works
Basically there is a neutral switch attached to the gearbox that when you shift to neutral it grounds a circuit to the ecu telling it maintain the engine idle speed / inject fuel etc
the other one that does this is the clutch switch (uses the same circuit if I remember right) when the clutch pedal is up the circuit is broken and ecu can see the car is running normally driving along and it won't attempt to correct the idle when you push the pedal down the switch is activated and it grounds the same circuit as the neutral switch and this tells the ecu, ok i need to maintain the idle speed now and inject fuel as apparently when you lift the throttle above certain speeds (over-run) the ecu stops injecting fuel which you would probably do when coming up to a junction, unless at Mcdonalds.
Thats why it stalls as the ecu just sits there drinking tea because it thinks the momentum of the drivetrain? will keep it running but when you clutch down you've knackered that idea!
So to fix it all you do is unplug the connector in the footwell going into the switch, use a 17mm spanner i think it is to undo the nut, twist the switch anti clockwise to remove it (its threaded into its bracket and the nut locks it into place) once its out get a small flat blade screwdriver and prise the metal tabs that hold the switch together until the swtich comes apart, then remove broken spring, clean any contacts that look crap and replace the spring with a clicky pen spring! nice and cheap! then bend the tabs down again and refit! i tried to align mine so that the switch was fully pressed and depressed when the pedal was up and down, you'll know what I mean one you see the little rubber pad the pedal contacts or just remember where yours was before you take it out.
That should hopefully solve it! Although I haven't actually tried driving mine again yet as I'm fixing other things but I'll let you know when I do unless you do try it first. its all over miata.net and other 5 forums anyway.
don't buy the clucth switch from autolink part n.o B001 or whatever it is, its the damn brake light switch! (think it might be a clutch switch in the bongo) I think its LA01 you want if you can't be bothered taking it apart and finding a spring from a pen
The neutral switch rarely fails from what I read and its easy to test as I remeber when out in mine I would shift to neutral when coming to a stop to stop the revs dropping or sometimes even stalling under hard braking! Only realised that after I bought one though and saw it was a bit of a pig to replace and thought sod it!
There is also a way to test it with an LED light in the diagonstic box on early 5's from what I've read, by placing it between MEN and GND i think it is and then when you press the clutch or put it in neutral the LED should light up showing the switch works
Edited by Birdster on Tuesday 23 February 17:13
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