Engine braking misfire S1

[Madfish.]

I have had a bad misfire/lumpy idling on a few occasions but not been able to isolate the cause. today it happened again, following a motorway run, I took a long exit sliproad at a "brisk" pace (may have been due to the Audi RS4 behind!) came off the throttle - brake - down to 4th - engine brake - brake down to standstill for lights. setting off from the lights it was lumpy as hell with jerking and misfire etc.
Now that the car has been parked for a few hours it is back to normal.

Its a 1999 S1 Elise, anyone any ideas what may cause these symptoms?

Edited by Madfish. on Wednesday 23 September 00:06

[Esprit]

Wonder if it's the MAP sensor on the way out, or water in the MAP water trap. The high vacuum on the engine-braking might be upsetting it and taking it out of tolerance.

My old S1 used to develop a misfire on odd occasions at seemingly random times....nothing major, and it used to go away if you turned off and restarted the engine.

[Scuffers]

if it's intermittent and seems to be at specific rpm's.crank sensor is my first guess...

they do seem to get progressively worse as they die...

[dunxS1]

If you're near Huddersfield you could have a word with http://www.fouldsmotors.com/
probably have a good idea.
Dunx.

[Madfish.]

Scuffers said:

if it's intermittent and seems to be at specific rpm's.crank sensor is my first guess...

they do seem to get progressively worse as they die...

Not intermittent as such,the previous time I recall it happening (about 2 months ago)was coming down Garrowby hill - again engine braking on a hot engine.

[Esprit]

Madfish, easiest thing to do for a start is take it to a Lotus specialist and get them to put the Lotus Check Scan tool on it. If your MEMS is holding onto any errors, then it'll show up here and maybe give you an idea of where to start looking.

[davidf4]

I had a misfire on my S1. First noticed it after a motorway run one morning. Once in stop start traffic it would miss when pulling away and reaching about 2000 revs. Power would drop off and the car would bog down. As the revs climbed higher the problem would ease. Parked it up at work. Coming home that evening problem was gone.

No problems for a while and then it did it again one morning. Off the motorway, accelerating away from lights, misfire at a given number of revs.

I noticed that on both days it had rained heavily in the night and the car was parked outside. The problem was simply water getting under the plastic plug cover on top of the engine and into one of the plug wells. Obviously the top of the engine is exposed to rain under the boot lid grill.
I'm not sure if the motorway work was causing water to move around and collect in the well or not, but the higher revs on the motorway would probably have masked the problem until I had to use the car at lower revs in traffic.

Solution was to dry out the plug well and seal the plastic cover properly to stop water gettting in.

Something to consider perhaps and a cheap fix if that's what's causing your problem.

[Madfish.]

Thanks for the responses, I will contact Foulds as they are not too far away.


Esprit - your rebuild thread is fantastic, hope you reap the rewards soon!

[piooly]

You could have a leak on your exhaust gasket, check for hot air coming from where the exhaust manifold comes out of the engine. (do this when the engine is cold !)

Or

Faulty Idle air control valve located on the throttle body. Cant be repaired, new item would be needed.

I have had this fault on mine in the past. Cant remeber now but it was due to one of the above.