engine idea when put into gear

[garyt]

aha there IS a "neutral" switch / sensor on the gearbox violet / black wiring. along with the reverse switch and speed sensor
so this must be the culprit. sorry short of going outside and disconnecting it and seeing what happens... but it must sense when the car is NOT in neutral ie. when its put in gear, and sends a signal to the ecu = revs rise

[garyt]

from more learned people than me on mx5nutz ;-

It stops the ISCV from fighting against engine braking unless you are in neutral or have the clutch depressed.
Idle speed stabilisation in the ECU depends on several inputs (clutch, neutral, sidelights, air-con, blower motor, idle). There is a Switch Monitor diagnostic mode built into the ECU


The idle circuit is live in gear with no throttle so that the car doesn't stall and allow you to trickle in traffic

now how you stop it doing its thing I don't know

[metal matt]

So whiles it the garage today I had I little fiddle with this. So my symptoms are when the car is running it is ticking over nicley. I can push the clutch in and out with no change to the engine Revs. When I put it into gear the revs go up by about 300-400RPM. So I found the plug for the clutch switch and had a play I connected it up to earth and when I put it into gear the revs do not change so happy days. The thing is I am now going to have to find a permanent fix for it. Options are leave it connected up to earth and see if I get a code on the ECU or by a switch and try and fit it to the clutch. Or myby something else .

https://haynes.co.uk/forums/showthread.php?t=13262
https://www.flickr.com/photos/124541083@N02/

[garyt]

hi glad you found it I may try disconnecting the neutral wire and see if the same result... but its buried.... so we will see .
as far as I can work out both instigate the icvs (idle control valve system) which is basically an anti stall via the ecu.

[Numplumb]

The neutral switch and the clutch switch and cruise control are spliced together in the loom and go to the ecu.
I think the clutch switch is a push to break switch, not sure about neutral switch but probably is the same, the other side of both switches go to ground so they are holding something low until you change there state by pushing the clutch or putting it in gear.
I would think the clutch switch could be done away with but not the neutral switch.

Google the Miata King Mike he has a you tube video about the neutral switch jamming the gearbox in reverse.

[garyt]

just watched the video you recommend and it highlights a problem with the selector jumping inside the box, thus sticking in reverse, sorted by poking in the reverse switch hole.
he also highlights the other switch "neutral" and explains it is used for idle control and emissions via the ecu
. so with the other searching Ive done , yes your right that the different switches trigger the same icvs in the ecu. I guess I need to try it and see, my clutch switches are bypassed which only leaves bme with the neutral switch so when I push the clutch in = no change to the idle speed, however as the OP when I then put it into gear there is an approx. 300 rpm increase take it out and the revs fall back to a steady idle.
I guess it is a try and see one as no other car I have had has had this and they have all driven fine