Hi there
Has anyone had the same experience as me?
(1) ENGINE RUMBLING: The car has worked fine for years but has developed a funny sound on start-up where it feels as though the engine is struggling (sounds like a gentle rumbling and not the usual smooth engine sound). It still works at these times (ie. will still move) and unless acceleration is depressed more than normal whilst the car is moving then the engine starts to cut out with the car feeling a bit shaky and then the engine does then cut out seconds or up to a minute later, with the car then stopping completely. It might then start again (but with same rumbling noise) and will same rumbling noise continues or might not start at all but it never restarts immedaitely without the rumbling sound. If it doesn’t restart then it will restart again but has to be left for about 30 mins and when it does then start (ie. having been left) then it starts fine ie. no rumbling sound.
This rumbing noise usually lasts for around 2-5 mins whilst driving but it then itself suddenly stops (that’s if the acceleration has been depressed much so that the engine hasn’t itself stopped in the meantime), the car feels like its had a split second change and the engine then runs as usual a second later (almost as if a switch has been flicked) and will then be ok for a few weeks until the same process starts over again.
The recovery service say the cause is different things, each of which have cost me but to no improvement. It was checked thoroughly by a garage whilst getting some paintworks done last year but they said they found no sign of the intermittent fault and, when I got the car back, it ran for months ok. In the last few months this intermittent problem has been re-arising again and its now happening about 1-2 per week. In the worst occasion this week, whilst I was driving it with this rumbling sound (ie. waiting for the rumbling to go a couple of minutes later), masses of steam started coming up from the bonnet (first time ever), the rumbling then stopped and the steam stopped as well (all happened fast) and the car ran ok afterwards until yesterday when it was working fine but then just wouldn’t start at all when I returned to it. Recovery guys said yesterday that they’re sure its the crank shaft sensor (but the previous guys were sure it was xyz before and it always proved to be wrong).
(2) DIAGNOSTICS MACHINE: Along the way, different people have said that the only way to be sure of the intermittent’s fault cause was the car put through a diagnostics check. Easier said then done and enter problem no. 2: difficult to find a mazda specialist with a diagnostics machine that is for my car’s year of manufacture because apparently the diagnostics machine changed about the time/or shortly after my car’s manufacture and the current machines don’t cover my car!! Recovery service now think they’ve found a garage with the right diagnostics machine (which they’ve verfied from the car’s chassy no. - a point I learned along the way this mornng from a kindly garage guy and which I relayed to the recovery service to attend to). If this garage does now have the right diagnostics machine then hopefully the cause of this intermittent fault will now be stated once and for all but I’ve had such a bad time with so called specialists that I’ve come this site to speak to mx5 fans who I’m hopeful will be able to give me some guidance.
As you may have realised, whilst being completely in love with my car, I’m not technical at all!
Hoping someone might shed some light on things for me.
Many thanks 
Julia