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Hi all, First post for me...been trawling for a while but decided to join for some much needed answers and knowledge - any help or decent advice from mechanical minded individuals will be greatly appreciated.

This may belong in electrics so my apologies...and sorry about the long post, might aswell get it all out the way now...!

Basically to cut to it...I recently bought a 2002 NB 1.8 6spd Manual, Midnight Blue Mica, beautiful and tidy and only 67,000kms!!

Anyways I have one issue, since buying it - it's been a tiny bit sluggish in low gears, more so when the engine was cold but here in Townsville it's been about 35c lately. It seems to happen the most when in second...for example: you're rolling along quite slowly about to swing it onto your driveway, as I apply a little gas, it chugs, just a little. And even when normal driving it seems to not really give me any 'boost' until around 3-4rpm. Now I realise this car in general doesn't start moving until you get to that range anyway, but low gears just seem to lag a little...

So far:

- Replaced the spark plugs, all 4 with Iridium IX11's. They hadn't been changed in a while
- Checked Ohm's of the 2 leads and the small one is showing up around a steady 3.5 ohms and the longer one around 9.5.
- (Fuel filter hasn't been replaced in atleast 20,000kms I think??)

So questions or advice needed:

1) Spark Plugs (BKR5EIX-11) - it say's on the box that these are pre-gapped at 1.1mm - however when I checked the gaps, they seemed slightly less than this between the tiny point and the other element, is this normal for Iridium's, or indeed do i need to ensure I widen the plugs? (I put them all in as is!) Is the gap the same type of gap as it would be if they were standard plugs?

2) Are the Ohms of the leads normal? They do look old but I can't seem to find any decent supplier of these leads in Australia, without ordering them through Mx5mania for around $75 for just the two wires, The only model I can find that looks like it would fit right are the NGK ZE76's, (order from US???) the Magencor 8mms are available through MX5mania - allbeit, not with that 'shorter' wire. So second question - Should I replace the leads? If so which exact ones should I get?

3) I today pulled out the plugs again as it did seem to get a bit worse since I replaced them, they had black deposits all around the ring and they're only a week old - is this normal? Is this a sign of the underlying problem?

I have also recently tried going from 95 RON to 98 RON in a bid to help the problem, could this have also affected it?

Sorry about the essay post! Any help would be greatly appreciated!!! Cheers.

Welcome & congrats on the purchase.

If the plugs hadn't been changed in quite a while then likely neither have the plug leads, so definitely replace them. Sometimes plug leads can test ok, but break down under load. One of the NB8B onward owners might be able to suggest a good supplier for the NB8B onward specific plug leads. But MX5 Parts UK are popular for a number of things: http://www.mx5parts.co.uk/leads-plugs-c-53_287_219.html

As a general rule you can't test plug leads with a multimeter unless they're seriously broken. Their resistance/performance at the 2 or 3 volts supplied by a multimeter is entirely different from what they might do when carrying 20,000V from a coil. Either replace them or have an auto electrician test them on a proper piece of test equipment.

Is your check engine light coming on at all? and have you read your engine fault codes?

Hey. That was going to be my last question. There is no check engine light and I've been debating also whether to purchase an OBD connector, but would it be worth it?

I thought of valve timing problems as soon as you said chugging . Seeing that it's a VVT engine I started searching for something that upsets the VVT actuators and found that 2002 models did have problems, often associated with poor oil or oil change history. It usually throws a P0012 fault code. I don't have direct experience of this problem, it's just a shot in the dark Try googling "VVT stuck site:miata.net" and you'll see what I'm talking about.

OBD2 readers are handy if you like playing with that sort of thing. ELM327 ones are cheap as chips on ebay etc. Somehow I doubt they're going to tell you much this time though.

I'm new to Mx5's so not sure what plug you should be running but are the plugs you have chosen too "cold". Cold plugs will do what you have described. Do the IX 11's mean 1.1mm gap or are they the same classification as the NGK 11's which are way too cold for even a race car. Make sure you gap the plugs as per manufacturers recommendation. Something as simply as plug gap could cause you issues whereby you replace everything and get to the plugs last costing you lots of time money and a lot of head scratching before you sort out the problem.

Regards - John

They are the correct plugs.

Other things you can try:

coil packs
cam angle sensor
battery
O2 sensors
Air filter
Clean the throttle body