Hi Guys
A bit of history: So, in November last year, I took my MX-5 off the road for the winter. After the winter I found that the battery had died completely (fogot to disconnect it… DUH). Anyway, replaced it, as it would not re-charge, and got it running again. I noticed the engine running a bit rough and it was a bit smokey coming out the exhaust. On top of this the revs plummit when I come to a stop and disengage the clutch. It has never stalled but it does come close. Once stopped the engine recovers and the idle is normal to about 800 revs.
After replacing the 4 spark plugs (1 was different and twice as long as the other 3 !!!) I ran some injector cleaner through the car and the engine runs MUCH more smoothly and the smoke has almost completely dissapeared. I still have to change the air filter and perform an oil/oil filter change with use of engine flush).
However, I still have an issue when coming to a stop with the revs plummiting to below 400/500 and almost stalling the engine. Even if I only disengage the clutch for the last 2 seconds before stopping it still happens. Once the engine has heated up it is MUCH MUCH less severe and drops only 50 - 100 revs more than normal.
Does anyone have any advice?
Thanks
Toby
Maybe the idle control valve needing cleaned or replaced.
Have you tried resetting the base idle?
http://www.mx5oc.co.uk/forum/forums/t/206.aspx
Sounds to me like classic symptoms. When the battery goes completely flat for a period of time, the base idle setting would have been lost.
Would this not then give a low idle constantly? It idles properly when I switch it on, as it warms up and when its got to temperature. The revs drop as i come to a stop then return to normal once stationary.
Thanks will give this a go
It’s probably worth trying the easier and more obvious solutions to this issue first but I imagine you will learn a lot whichever way you decide to deal with your problem - good luck 
Cheers Rhino.
I take ages to do anything as i will change 1 thing, check if that changes anything, then try something else and check its affect etc etc… result studying chemistry at Uni and then working as an engineer in a foundry!
Will eventually get to the problem/fix and post it here
I know what you mean
Went from IT contracting(10 years +) to fencing contracting - life can be a bizarre experience if you make it so:-)
Base idle problems, from my experience with the MK1 are typically what you describe. An engine at optimum temperature that if revved, drops back to say 5 - 600 before settling at normal idle. It’s the ECU having poor communication with itself and resetting the base idle will cure the problem.
Not sure about the MK2 but the IAV on a MK1 plays up on startup usually, over revving at 2.5 - 3k before settling when the engine is getting up to temperature.
Do you have an LED tester to interrogate the diagnostics on your car? The MK2 is much more fun than the MK1 with lots more codes:-)
I was going to look at the ICV last night but it started to rain 
Was already cold so stayed in 
My Mk2 doesnt over-rev at all. on start up, engine gets to 1200 ish revs at cold nice and easy, as it warms up, it drops to 800 ish steadily no problems. Its only when the engine has only ‘half-warmed up’ (if that makes sense) that i get the dropping revs when coming to a stop.
As for the LED tester I dont have one
I read the base idle reset guide, but I dont know how to adjust the base idle itself? is it a case of adjusting the valve and watching the rev counter?
Thanks
I made my own LED tester but Andy at Autolink sells them together with a list of codes, so all you need really.
As regards adjusting the base idle - yes that’s right. Its a flat screw from memory - may have a plastic cover.
Before buying/adjusting/changing anything, try THIS:
mx5oc.co.uk/forum/forums/t/59084.aspx
Worked for me, and seems to be a common occurrence after battery disconnection, almost as if the ECU temporarily loses the current idle setting & goes back to basic setting.
Any comment from the experts? (cos I ain’t one!)
Bill
Hi Bill, sorry to revive a super old thread! The link you’ve shared seems to not exist anymore - I’m having similar problem to this post where my rev drops quite significantly to the point where the car stalls (together with when lights are on etc where my revs drop quite a bit some times).
Checked voltage at terminal reads around 14.98V with engine on , which is a bit high but not toooo high so my battery light hasnt gone off. Since then I’ve changed battery, alternator, grounds on PPF, next to dipstick, on manifold to no avail.
Is this similar symptom to what you experienced? I’m going to try resetting the ecu tonight (guessing that was what the post you sent was about?).
Or if anyone here knows what I could do to have this fixed? Thanks in advance!
A bit late in replying, but if you’ve had the battery off for any reason then this idle issue is common. You need to allow the car to tickover for about 20 minutes.
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Thanks for that! I’ve reset the idle today and all seems to work ok, hopefully no further issue 