Engine splutter and idle issues.

Our drive home from the IVA at 50mph.

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Oh joy of joys, the day of the IVA. Driving to the test centre, leaving home at 5am to get to the centre a whole 50 miles away. We got onto the open road, got the car up to speed and…. Oh we cant do over 2000 RPM. As soon as we do the car splutters like its hit the rev limiter.

Quick! Ahift to the next gear in quick secession and up into 5th so we can get over the Dartford crossing before 6am when charging starts then pull into an industrial estate and hope we can spot a quick fault. Sadly, the ordering of the spark plugs in the engine bay were spot on, there was no clear and obvious leaks and nothing disconnected, so we couldn’t fix her by the roadside so easily.

So, we checked everything over, made sure all the cables were seated and set off again. Not much better luck here, we got a little more RPM out of the engine but were still limited heavily.

A few more miles down the road we found a motor factors, managed to replace the Spark plugs and the HT leads, hoping perhaps that the old 100,000 mile parts in our old 1.8 engine might just be tired. Unfortunately as we pulled out the spark plugs in the carpark of a motor factors in Rochester (https://www.aghabridge.co.uk/ who were super helpful) and were open at 7am with some spark plugs in stock, we found that plug 3 had unburnt fuel in the chamber.

Replacement HT leads and Sparks didn’t fix this issue and, we are now left diagnosing the issue again before we go for a retest, as the car wasn’t able to reach 70mph. At the present time it could be any of the following:

  • Poor Coils resulting in a bad spark -Poor vacuum hose connections resulting in a poor/rough idle. -A faulty injector causing poor vaporisation of fuel.

We will be testing these shortly and I will try and do a guide as to how we tested and diagnosed each part.


We also discovered that the aftermarket fuel cap “locked”, but was crap for 3 reasons. For the IVA a fuel cap must:

  • Lock or be tethered to the vehicle in some way
    • Where it locks, it must lock and the key be removable only when it is locked. So you cannot drive off with the key in the cap dangling from your steering column
    • Prevent fuel from pissing out of your tank….

Ours didn’t really do any of that. As a little hint, if you have an MX5 it will have a pressurised fuel tank that hisses slightly when you open it, and that normal. This means if you have a cheap knockoff, and it doesn’t seal, it will leak fuel everywhere. Buy an original one or one from a breakers, these breath slightly and let pressure out but also give a good seal.


So, whilst we made it to the IVA test centre, slowly, we did not pass. BUT, I wanted to share some unofficial info, to stop those of you that might get heartbroken by failing first time or getting a big list of advisories.

Our tester said that in his entire experience, barely 2 vehicles have passed first time. This is not a sign of his being “picky” or failing them because of officious rules, but just a sign of how high the bar is for a pass. So, dont expect to pass first time. Its bloody unlikely, even if its just some comments about radiusing, It probably wont sail through, so, dont get cocky.


Welcome to Twits with Spanner. A blog following two chaps as they attempt to build an Exocet kit car with bits from a donor MX5, spanners and lots of hope. Read more about us