Went up to Jack Smith’s in Swansea to get a new soft top yesterday (thanks for the recommendation Mal), great work.
However on the way home got into some stop-start traffic and the revs started going all over the place on idle. Really erratic dropping to a near stall, up and down very fast, going up to as much as 2000rpm. Stopped the engine, had a look, gave it 5 minutes and it was fine until later in the day when the same thing happened.
Revs all over the place, very difficult to start, either just kept turning over or died the moment the engine fired. Kept giving it another go every five minutes or so. Got it to start with the same erratic revs, undriveable so waited another 10 minutes and it was fine, got home an hour away with no issues.
There are no warning lights at all.
Earlier in the week I had the top rad hose fail so I changed the top and bottom hoses. I had to take off the air box, intake, washer bottle and horn to get room to get at the bottom hose, so thought I might have knocked something like a connector but cant see anything wrong at all.
Hmm, you have dismantled quite a lot of the air inlet system. Is it still sufficiently airtight at the joints? Or has a leak been introduced at one of the many hoses, both big and small?
Also, another possibility, are all the plug contacts for the various sensors and controls on the air system nice and clean? Some Servisol contact cleaner can work wonders here, specifically designed for the job it is infinitely better than WD40 which is a rather good insulator and waterproof glue.
Detach the air ducting after the Mass Air Flow sensor and spray cleaner into the ducting.
Just follow the instructions on the can and keep the revs up.
I tried to clean 2 of these iscv, ended up getting a working one 2nd hand… its not worth trying to clean is the moral of my story! (But you may have more luck!)
I’m still getting this problem now and again. It only ever happens after a long time in stop start traffic. I’m guessing it might be heat related, not that there are any overheating problems since I changed the radiator.
I am starting to think it may be one of the coil packs on the way out, I think the NB has 2 coil packs side by side in the unit behind the engine. If that’s overheating and causing a misfire then I suspect the revs are going all over the place as the electronics try to cope with it.
The coils on that age MX-5 do give trouble, what you’ve said is feasible. It’s strange that you’re not getting low power issues when pulling away while it’s “misfiring”.
Maybe I’m not describing how severe the problem is. There really isn’t any power or drive-ability. Once the revs start jumping all over the place the only thing I can do is use a bit of clutch to get the car to the side of the road - it’s always at low speed. It will eventually stall after about half a minute and then it’s dead and wont start for 15 or 20 minutes. In that time it will crank but doesn’t fire or if it does fire it will die straight away.
Check all the connectors on the engine especially the crank and cam sensors it sounds like a connector going open circuit when hot make sure all the contacts inside are nice and tight with now gaps between them
I think Robbie has pointed you in the right direction on this. The coil packs are the single most unreliable part on an NB. Don’t buy the genuine Mazda part it is way over priced and and not that good. One off ebay for around £60 will do the job. I’ve had one on my car for a good few years now.
I have the same issue with my newly acquired NB 1.8 16v. When I got the car last week it had a cone/pod filter, gave a great induction noise, but I suspect was just pulling nasty hot air off the manifold. Had the stalling issue 3x when driving in stop/start traffic. I have had the pod filter removed and a standard air box installed (with a new K & N panel air filter) a days ago, and have not had it happen again, but am paranoid it could, and I would like to replace the parts you have just in case.
Have you had any reoccurrence of the issue after making the changes above? Also just to clarify: CAS - Cam Angle Sensor, CPS - Crankshaft Position Sensor?
It hasn’t happened again so it’s been good for about a year. Yes, you have the CAS and CPS right. I don’t know as I replaced CAS/CPS and Engine Temp Sensor at the same time but my gut feel is that it was the Engine Temp Sensor. These were all tested used parts. You could save money by trying one at a time.
As others have said it could also be coilpack or leads which I had already tried, but the revs going allover the place fits with sensors/engine management. Unfortunately it’s try changing things until you find the bad one.
I have a very similar thing happen in mine but not anywhere near as bad. It’s always when I start the car up and if I sit there for a few seconds without setting off the revs drop to almost a stall and stays there a little and will rise again. If I remain idling then it will go again but never stalls. But this is the only time it happens, after setting off I don’t get the problem again. Even with long spells in traffic it remains stable.
Did yours deteriorate over time Tim?
To be completely honest everything mentioned in this thread went completely over my head (in terms of the reasons and possible ways to overcome them). At the moment it’s not really a problem but if there were something I could do to stop it getting worse then I’d get it sorted even if it cost me a few quid. Someone recommended cleaning the Idle Air Control Valve so I’ll have a look to see what that is and how to do it and give that a try
It didnt deteriorate it just happened now and again. Yours sounds like the idle, I would read here on setting the base idle and cleaning the IACV and throttle body isnt a bad idea. Loads of info on here if you search or ask.
Cheers. Yeah will do, I don’t think I’ve had to really ask anything yet due to there already being the info available already somewhere on here.
I hadn’t even thought of it being a problem and don’t think I’ve even mentioned it to anyone but when I read what yours was like I just thought ‘that sounds like mine’!
Update on my issue. I had the crank sensor replaced, seemed to be ok this week driving to and from work, although the idle seemed a little rough. I was driving today and it stalled out again. Called out RAC to check things, asked him to check the installation of the crank sensor to see if it was an alignment issue. He checked the gap and made an adjustment. then driving home, once again in stop/start traffic it happened.
I feel like it is some kind of air issue, as it only seems to happen it hot weather, when the car is not moving fast so little air coming in. I have a diagnostic check booked on Monday, so hopefully I get a guru turning up who can figure it out