Hi there! I own a MK1 95’. My idle behaves a bit ackward lately. When i’m stopped in a stop light for example and i DON’T push the clutch, then i might get a drop in the idle. It might go between 350-700. If i’ll push the clutch then the revs will go normal![:^)]. If i’ll let the clutch again the revs will drop and so forth. The weird thing is that this is not a persistent behaviour. Sometimes it will behave normally. I have also observed an idle drop when i’ll pop up my lights, but this isn’t happening all the time as well. I haven’t tried to adjust the idle with the procedure specified in the HOW TO’s, since i just want your opinion first.
Set the base idle first and then see what it’s doing 
My idle and electric windows behave erratically when cold and first starting up. The windows stick halfway down or just before fully down. However when the car is warm then both are OK. Not on this car but on others I have noticed that when the lights are on the idle goes down - in all cases the battery has been a bit old and maybe drawing extra current to get to full charge but after a few miles there’s enough to keep everything going OK. My 5 is a '96 model with original battery AFAIK. If yours is original maybe check the charge rate/voltage?
What do you think Geoff?
BB
There’s a little spring-loaded push-switch on top of the clutch pedal - the spring tends to break in half meaning that the switch doesn’t work correctly, even though from the outside it still appears to spring in and out a little bit. The switch just unbolts (take note of the exact position first) and then you can fix it with the spring from a ballpoint pen, and after fixing mine the clutch-related revs behavior got much better.
Good tip Jim, do the idle setup first and then check the clutch switch, there’s a link here to some more info
http://mx5oc.co.uk/forum/forums/t/231.aspx
Will do guys and i’ll let you know! Thanks for the tips!
Ok guys, i adjusted my idle as stated in the howto’s section. With my engine running in operation temperature, i grounded the TEN (Test ENgine) and GND (ground) connection and then adjusted my idle. It goes ok until know. But there is something that makes me think that this solution will be temporary. I tried to check the clutch behaviour, not only in idle but also with some revs in my engine. The same thing happened! I had for example 3000 rpm and when i pushed the clutch they went to approximately 3250! I released the clutch and they went back to 3000!
So i’m guessing that i’ll have to fix the clutch switch as well, under the dash. There is a relevant howto here. The fix is simple, just replacing the spring inside the switch with another from a pen! I’ll keep track of my work…
I have a very similar problem, every now and again when I place the car into gear just before pulling away, the reve drop to ~350. If I take the car out of gear the reve return to normal. My temp fix is to have the aircon running as this increases the revs to cope with the extra load. Not a perfect solution. I read with keen interest, the comments about the clutch switch. What is the switch for by the way? I am going to have a looksee this afternoon and I will post the results here.
From the engine faq…clutch switch
“On the over-run above a certain speed, the PCM will not inject fuel. However, if the clutch is depressed the switch tells the PCM to keep injecting fuel so the engine will idle, otherwise it will stop dead and you’ll lose brake/steering assistance, your headlights will go dim and you’ll experience quite a jolt when you let the clutch out (although the engine will generally bump-start itself).”
Tomorrow i’ll try to remove the clutch switch, as the problem insists. After two days of normal behaviour, today i noticed idle droops again. So the next step is the clutch switch. There is 17mm bolt that holds it in place, however the space there is small, and i couldn’t unscrew it. I’ll try again tommorow in daylight. I’ll also try to clean my butterfly, in the throttle body, and i’ll keep in touch.
Info here
http://mx5oc.co.uk/forum/forums/t/233.aspx
Be careful cleaning the butterfly, ISTR there is a black material around the edges of the butterfly itself. This aids in sealing the orifice when the throttle is closed
Here was the situation. If i would stop for example in a stop light
lets say, and i wouldn’t push the clutch, my idle would drop at aprox
350 (first line in the rpm meter) and would stay there. If i would push
the clutch the revs would build up to aprox 750(second line in the rpm
meter). As long as i push the clutch the idle speed is stable at 750.
Release the clutch and the revs will drop again. I tried 3 different
things:
1. Clutch switch: I removed the clutch switch, hoping that the
spring inside would be broken, but no. Just a little bit of grease that
i cleaned.
2. Throttle body cleaning: I removed the air intake in front of the throttle body, with the engine turned off and sprayed with a cleaner. A lot of grease was removed.
3. Idle speed adjustment:With the TEN and GND connected in the
diagnostic box, and with the engine running in operational temperature,
i adjusted the idle speed from the idle adjustment screw.
At first the problem seemed to have been cured. But after two days of
normal behaviour, the idle would drop again. Anything else to look? Any
instructions to where the ISCV is located in order to try and spray
some cleaner there too?
The IAC valve is underneath the throttle body. When you take the crossover tube off the throttle, you’ll also have disconnected the pipe underneath it (about 20mm diameter) which feeds air into the IAC. If that valve’s gummed up, it would prevent the ECU from being able to adjust the idle. I once fixed an idle problem by spraying copious amounts of cleaner into there and letting it drain out. The engine coughed a bit at restart as it inhaled the residual fumes, but it soon cleared and ran great. Mazda call it an Idle Speed Control valve on the 1.6 engine and an Idle Air Control on the 1.8, for reasons best known to themselves. The 1.8 version integrates both the solenoid controlled valve and the thermal valve (“wax” valve, for cold starts) into one package. The 1.6 version has the thermal valve separate, bolted to the inboard side of the inlet manifold. Hope some of that’s useful.
In order to remove the big air tube in front the throttle body, i had to unscrew one bold that holds it in place and remove a smaller tube, on the down and left side of the throttle body. Is the ISCV there in the end of the small tube? Remove the tube and spray there?
That’s right. Spray into the stub that the smaller pipe was fitted onto. The IAC valve is inside the casting bolted onto the underside of the throttle body. The black plastick lump sticking out of it is the solenoid which the ECU drives to open and close the valve.
Food for thourght… The cluch switch works alongside the neutral switch, the PCM needs to know if the car is in gear as well as the clutch pedal position. With the clutch pedal released if the PCM thinks you are in gear it can do funny things to the ignition timing and this can affect idle speed. Have you tried a switch test? See “-halli- switch test” topic on the old forum.
Ok guys, both my clutch and idle switches were ok. So back to the
engine. This time i had the help of a good friend, who also owns a MK1.
This time, we cleaned both the body throttle and the ISCV, with
the engine running. We used a carburetor cleaner, as mentioned before.
Not to mention how much of dirty smoke came out from the exhaust! This
time cleaning was really good and deep.
We also did one more thing that my friend had already done in his own miata. We cleaned the air flow meter.
If you open the air flow meter, you will also see dirt inside, but the
most important is how easily the flap that opens and closes inside the
air flow meter moves. Few sprays with WD 40, made it move much more
freely and easy. The car is now much more responsive, and the idle
steady! It is very noticeable how gradually my idle drops and stays in
the correct position. Previously, it would drop immediate, go below
500rpm, and stay there. Now, if I’ll push the throttle to lets say
6000rpm and leave it, it will drop gradually, and right about 1200 rpm
it will start slow down to stop at 850! Obviously, cleaning the air
flow meter, has also made its difference.
Next stop seafoam for a complete cleaning of the engine in the next oil change. Thank you all for your recommendations!