- My model of MX-5 is: 1992 NA Eunos
- I’m based near: South London
- I’m looking for technical help or recommendations on: How to fix the high idles/cold start idle fluctuations.
Hi. I got my mx5 a few weeks back with little to no history so had the timing belt/water pump/gaskets done this weekend. After this I did an oil change and switched the old plugs and leads for new ones (may be unrelated by my partner ran the car with the leads unplugged after the oil change). Since this the car now hunts on cold start - it will jump from ~1200rpm down to ~100rpm and continue for anywhere from 20-40 seconds before settling just above 1000rpm. If you apply a small amount of throttle it helps to settle this quicker.
Once the car is warm and driving the rpm sits anywhere from 1100-1500 at stand still, only dropping to 1100 after a minute or so. The car itself drives perfectly well, the only issue appears to be the idle.
Currently from other suggestions we have: Cleaned the AMF/Throttle body/IACV, changed the plugs and leads back, checked as well as we could for vacuum leaks/cracks in any tubes/pipes, checked the firing order. I have ordered a diagnostic tool so will check for codes as soon as that comes in, but for now, any ideas would be greatly appreciated 
Have you checked/adjusted the base idle by bridging the TEN & GND terminals in the DIAGNOSTIC socket and adjusting the air screw on the throttle body?
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Which gaskets did you change?
This sounds like there might be an induction leak somewhere.
Alternatively you haven’t adjusted all the slack out of the throttle cable, have you? It shouldn’t be pulled tight when there is no pressure on the gas pedal.
Hi, we had the timing belt/water pump done by the rocketeer guys so I believe it would be the valve cover and CAS o’ ring gaskets that they would have changed - I’m inclined to believe they did everything correctly. When we took the throttle body/IACV off we did 2 of the gaskets that looked worn/old - any gaskets we came across were replaced.
I will check this once I am home later and get back to you! Something was off about the throttle cable but we ran out of time yesterday so plan on looking tonight 
Thank you!
Hi! We had a quick look at it yesterday but we didn’t end up adjusting anything as it was getting dark/we ran out of time. I think I’ll have a proper look once I’m back this evening and see if it needs adjusting, will let you know how it goes, thank you!
Unfortunately no luck 
seems like the air is getting pass the throttle or smth of the sorts as car runs fine etc even when the throttle is supposedly shut and the screw is all the way in…don’t know all that much about it though. Cannot find leaks in the area either
I’d probably be suspecting a problem with the idle air control valve then. The first check is to check the resistance of it. From memory it should be around 12 ohms.
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Hi, we will do this hopefully today and may be back 
Checked the codes and have code 14 (atmoshperic pressure sensor) - from what Ive read thats on the ecu?
Yes, the barometric pressure sensor is integrated in to the ECU. If the code won’t clear, I’d check the ECU & connectors for water damage. Even if the code clears, probably worth checking the connectors at the ECU anyway if you’ve not already done so.
Thank you! Will most likely be taking a look at the weekend now but will get back to you! There looked to have been water in the passenger footwell based on the corrosion but the ecu looked clean on the outside. I believe it is some sort of aftermarket or altered stock ecu, cant find much info on it tbh