At Bedford on Monday my engine played up and I’m interested in all your thoughts for a fix.

It worked fine for about 4 laps (they’re long, 4+ miles) then the 5,500rpm limiter cut in. At this point the water temp was about 80oC and the oil probably low 90s. Sinclaires were supporting the day (and I was both highly grateful and impressed at their free service, would have no qualms about taking my car to them) and quickly spotted the connector to the air intake temp probe had come off. This seemed like a simple fix as it would have suggested that the ECU was getting upset at the point it started to read the air temp - yay! Sadly that wasn’t the end of the story.

Having done the ‘on ignition, 5 slow presses on the accelerator, off/on ignition’ ECU reset I went out again and the same thing happened. I returned to Sinclaires and we read the fault codes from the std Lotus 190 ECU (with safety re-prog upgrade). There were about 8 including things like ‘air temp fault’, ‘water temp fault’, ‘multiple random unknown misfire’ (nice one that ). We cleared them all and I went back out, it reoccurred, and I returned to have the ECU read again, it gave the same multiple results.

To try and see if it really was a misfire I felt the plug connectors and then ran the pyrometer over the top of the engine to see if there was any temp variation. The plug connector closest to the middle of the car felt hotter but the pyrometer showed a pretty even temp across the top. A bit of WD on the rear-wheel speed sensor and in the plug connectors made no difference (original leads BTW). [Big thanks to the Edwardz Boys for help with this part ]

The assumption was it was a silly electrical fault causing the ECU to get confused. The most likely contender was considered to be the Brown sensor so Sinclaires swapped it out - no change.

Interestingly, if I simply killed the ignition and turned it back on whilst on track (not overly recommended at speed!) the problem went away for a lap or so. Still, that’s hardly a fix you want in order to be confident braking from 130 in to a 90mph bend!

We couldn’t really get to the bottom of the problem, which is a shame as it seems like the type of fault that’s going to be hard to reproduce away from the track.

So, what are you thoughts? Any ideas/suggestions? Please bear in mind that I’m not overly mechanically savvy, so it may well need to be professionally investigated. But if there is anything I can either try myself or suggest to a whoever looks at it I’d be very grateful.

Does anybody know the temp at which the ECU starts to use air temp?

Thanks in advance.

Cheers, Ian


Can you borrow a rear wheel speed sensor, & try that?

Before anybody mentions swapping to a Honda I know its an option, and one that several have done when this problem has occurred, but funds don’t really allow at the moment.

I also wonder if swapping to an Emerald would help find or create the fix. That’s still more than I ideally want to spend but if it would also get me something more it would make it better use of money.

I could just change leads, plugs, etc and see if that clears it up, but the plugs haven’t done that many miles at all and I’d only want to go down that route if it was felt it stood a chance of a cure.


Can you borrow a rear wheel speed sensor, & try that?

I suspect I could.

Are they easy to replace? (as in at a track in a few mins)

Cheers, Ian


They’re not difficult to replace!

Also, check for chaffing of the wires as they pass through the bulkhead (from ECU to engine bay). I had that problem, which initially caused intermittant misfires, then went on to literally melt a coilpack! I appreciate that such a “check” may not be easy, but it needs to be done!

Good luck, matey, hope you sort it soon.


Did look for chaffing but it was a bit hot down there, so will get a mirror out and have another go.



Did look for chaffing but it was a bit hot down there, so will get a mirror out and have another go.


Also, the wires could be damaged inside the plastic covers, so a Multimeter may be required too! Any auto electricians nearby?


I have a rear wheel sensor - Its bagged up ready to go to SteveJ - but I guess he wouldnt mind you borrowing it for a bit - Steve ??

Can you replicate problem on the road though ??

With all those error codes a dodgy connection, bad earth or some chaffing sounds possible …

Cheers Andy but there’s no point unless I can recreate it. I’ll perhaps try at the weekend but I suspect it’s gonna involve a lot of low gear high rev running.



Try & find a bumpy road too. My misfire used to frequently show up on the A50 from Donington to Stoke - horrible concrete surface in parts. Obviously, the “bouncing” around was causing the wires to move about!!

A cunning plan, ta.


Ian - My Exige had intermittent misfire around 5.5k revs - after much puzzlement it turned out to be a dodgy MAP sensor hose - one had the slightest of holes in it. Been fine since I replaced it. Had to remove the hose as the puncture was on the engine side…

ps the hoses are the small dia black and white ones that link the throttle bodies to the MAP sensor.

PS - I have a spare coil if you want loan of it

Hope you get it sorted…

had same kind off problem butsince the emerald no problem at all (touches wooden desk lol)

There seem to be a lot of people getting issues like this.
Cutting max revs to 5.5k seemed linked to my wheel speed sensor becoming detached. Fitted back together but it had rubbed against the tyre and melted the connector somwhat.

Still getting idling problems though. Engine would be fine when cold but would die when warm at zero throttle and the car moving. Seemed to idle fine when stationary. Now it just over revs 2k+

I cleaned the IACV (but seemed pretty perfect).
Cleaned MAP sensor
Cleaned all the thin hoses from the head and MAP sensor (gunked up a bit and a slight horizontal split - fixed)
Checked the wires through the bulkhead (fine).
Reset the TPS (5 pushed of accelerator etc).

It revs past 5.5k but doesn’t idle right. So could be TPS is fubarred, wheel speed sensor is the same. Lambda sensor could be shot. ECU is buggered or any number of other things. Also have a hole in the manifold (so could be that).
MOT due shortly so hopefully Nick Whale will find the issue and fix it under warranty before that runs out this month.

I’ll post up if they diagnose the problem.

By all means try the wheel speed sensor that Andy D has to see if that’s it.


had same kind off problem butsince the emerald no problem at all (touches wooden desk lol)

ditto - mine has been great since fitting the Emerald and verniers

Well the Emerald doesnt “detect” any misfire like the Lotus ECU does so you wont get the problem

The idea from Lotus was to stop CAT fires I think … so a sort of insurance on their part…

Andy, are you suggesting there’s still a problem there with an Emerald or that the Lotus is crap/over-sensitive at detecting a misfire?

So what did people’s Emerald installs cost them?

Thanks all, interesting, delighted to hear any more.

Cheers, Ian

Ian, I was standing watching you do all this. I wish you had said because I had the same problem when I first picked my car up. I removed and cleaned the o/s rear wheel sensor and also wire brushed the gear it picks up on. I then WD40’d the gear.

I have never had the 5500rpm miss fire cut in since and it cost nothing to fix. Has to be worth a go!!!

Ian - I think the Emerald just does not have the misfire detection programmed in. Don’t forget it was an upgrade/revision to the original Lotus ECU.

I would not move away from the Lotus ECU until you have found the root cause. Just swapping to an ECU that cannot detect it does not sound like a good thing but if you wanted to do it, then a cheaper option would be to fit an older Lotus ECU which did not have the revision.


As Steve said

I have a spare 190 ecu, wheel senor and stuff - you can borrow it all … problem is you need to replicate the misfire ( or whatever ) is causing the ECU to go to “get home”.

I think if it was the connector then you would get the limit kick in almost straight away EDIT - I think you need motorway speeds to activate it as well … I remember when my sensor wire was off nothing happened until I got on the motorway … around town thrashing in lower gears and speeds didnt set it off !!!( my experience ) unless its a bad wire … but I think you had to do a few laps first ?? - If so it suggests something else like a sensor that kicks in after some time - see if you can get a pattern going and proove that pattern a couple of times - that helps to pinpoint the area …

Try it on the road - if its not there I would say its not wiring related …