I’ve noticed for a few weeks a problem with the idle speed on my 1.6 NA (a 1992 Eunos). It’s always been beautifully sweet at around 850/900 but it’s recently started idling at close to 2000, and even when the engine warms up, only dropping to around 1200-1500.
Today I at last got round to getting an LED across the diagnostics and seeing code 34 which I see is an ISC valve problem. I’m confused though - I’m hoping someone can shed some light here.
I’m pretty sure that if the ECU is reporting a problem with the ISC valve it’s going to be an electrical part, right? I’ve seen people writing about the part that’s meant to have a solenoid coil resistance of 11-13 ohm, and I assume that’s the one with the problem? This article https://www.miata.net/garage/isc.html suggests a replacement is going to be several hundred pounds - and not this kind of thing https://www.mx5usedparts.co.uk/mx5-mk1-1-6-icv-idle-speed-control-valve.html although it seems to have the same name…
Incidentally, I now seem to have a coolant leak as well, leading to overheating yesterday - I assume that’s a completely separate problem (which i haven’t yet had a chance to properly look for), but I mention it in case somehow it could be linked??
I used to have this problem a few years ago ( there is a post in the archives " high idle " ) solved it by replacing the the throttle body complete with the ISCV despite checking all electrics ohm readings etc.I would get the leak fixed first then look out for a 2nd hand unit ok
If you did not get an error code, the issue would very likely be the idle air valve that is bolted to the top of the engine and has coolant running through it.
Error code ‘34’ is no debate - the ISC valve has failed - you just need to replace it with a known working one.
There is a resistance check that can be done in the ISC valve - certainly worth doing that on any potential replacement before fitting.
One of the posts referenced above talks about a check on the ISC valve - warming up the engine then disconnecting the ISCV.
Can anyone point me to exactly where / how I can do this? My (limited) understanding is that the ISCV is on the bottom of the throttle body, and I can’t see that it’s accessible without removing the big air hose that feeds front of the throttle body.
I can’t find any clear pictures of where things are. The Haynes manual doesn’t help, calling the valve on the throttle body the IAC, which I think is in fact something entirely different on top of the engine block?
Despite the error code I’m reluctant to shell out close to £100 on a replacement ISCV without testing mine, both with this check of its operation and also with a ohmmeter.
Thanks Hilux … helpful, I’ll give that a go. I couldn’t find a coolant leak so I decided to drain and change it, and ever since then it’s been running super-smoothly with no over-idling. Weird.
Any chance that diagnostic code 34 could be a historical thing that hasn’t had a reset, or is it a live reading? Anyone know?
It is possible but unlikely. The code would reset itself if a good part was fitted or perhaps you removed the connector and refitted clearing corrosion off the contacts?
A major part of the throttle body - much easier to replace the whole throttle body with a known working complete assembly. Usually available cheap from the usual source or pay me more for a clean guaranteed item:-)