Coil Packs?

Hey guys, nice to meet you all, I’m new to the forums :) 

I recently acquired a 1999 Mk2 MX-5 from a friend as she is having serious issues with it and I’ve offered to look into it for her as she’s not particularly familiar with cars and her garage have been taking her for a ride. Here’s the back story…

When driving it from cold it seems fine, but if I take it on a short journey (say to the shops) and then attempt to start it up whilst the engine is still warm/hot it will often fail to start repeatedly. Once the engine has cooled a little it will start but then when driving it will shake and shudder and behave as if it’s going to stall when the revs drop below 1500. I’ve yet to allow it to stall as I’ve adapted my driving to keep the revs on when it’s doing this but I’m fairly confident it will stall if I let it and I know my friend has had it stall frequently. Also, when it’s doing this it has no power at all; it pretty much limps along with the revs topping out at around 3k even with my foot flat in 3rd gear. I’ve also noticed occasionally on longer journeys at speed you can feel mild shuddering but this clears up after a little while.

So far her garage has done the following:
Diagnostics threw up two codes:
 one for crankshaft and one for airflow. Replaced the crankshaft sensor; this made no difference. She was then told it was dodgy wiring; wiring was stripped for faults and was given the OK. She was then told it was the air flow meter, she replaced this, it made no difference. They upped the idle to stop the car from stalling, it still stalled. She was then told the CPU was duff at which point she gave up. She then mentioned her problems to me at work and I said it sounded like it could be a coil pack fault; she took it to a new garage who gave the coil packs a clean and the car seemed better for a few days but then the problems returned. Her new garage have quoted her £500+ to replace the coil packs. My only point of confusion is if it is coil packs, why is it throwing codes for crankshaft and airflow?

It seems like there’s a common issue with the coil packs on the Mk2’s from what other mx5 owners have told me - is this the case? And if so, does the above issue sound likely to be the coil packs? Any advice really appreciated :) 



 The first thing to do is check for fault codes.  This is possible with an LED and a bit of wire, there is a “how to” on this site somewhere.


Thanks Alan! The codes have been checked and apparently the ones it’s showing are for crankshaft and air flow - thus the crankshaft sensor and air flow meter being changed. But neither seems to have solved the problem :frowning:

 We need to know if the codes are still there or if the replacement parts have cleared the codes.  It may be necessary to disconnect the battery in order to cancel any pre-existing codes and then run the engine and check for new codes.


Thanks Alan, I’ll disconnect the battery to clear the codes off. Only problem is I don’t have an OBDII reader to read them again…

 If its a 1998 car then its not OBD2.  That did not come in until the Mk2.5.  The codes can be read by connecting an LED to the diagnostic connector.  Autolink sell a suitable set up very cheaply–mk2-6665-p.asp   You might want to buy the manual as well.


Hey again, thanks for the advice and sorry for the delay, I was waiting for the LED code reader to arrive.
I just went out to read the codes however and the LED never lights up :(
Here's what I did:
1. Disconnected battery and pressed brake pedal for 10 seconds to ensure codes were cleared.
2. Reconnected battery
3. Connected up the jumper and LED on the diagnostics box as per instructions
4. Turned on ignition without starting engine

Results... LED failed to light up at all, not even to show diagnostics were connected. 
Is this because there are no codes or am I doing something wrong? :)


LED’s are polarity sensitive, if connected up wrong way round they will not illuminate. Are you sure it is connected the correct way?

PS I am by way of being a relative beginner at this diagnostic malarky, so if anybody with more experience would like to jump in I have no objections.

Thanks Alan. I’m fairly certain I connected it up the right way around but I’ll try the other way around this evening just to be sure that isn’t the issue :slight_smile:

 Agree with Alan on this one.

The only time my diagnostics failed was on a MK1 when the air flow meter was shorted out to earth.  

Hey guys, just an update as I don’t like to leave threads without a resolution like this one.

I did have the LED kit hooked up correctly as far as the instructions were concerned but it looks like whoever made it put the coloured insulating tape the wrong way around as when I switched the LED wires to be the reverse the LED worked - so thanks for that!
Diagnostics showed up no codes at all and after an inspection, the ECU seemed fine. I ordered a second hand coil pack for £60 from a Mazda breaker and fitted it and the car is now cured so this was definitely a coil pack issue.

Thanks for your help! 

Thanks for the update, good to know you have fixed it.