MX-5 rough idling

[swansea v6]

Ever since I have had my little Eunos the idling has been a bit rough, usually hovers around 1000rpm and is quite lumpy. As i have never had one before I just assumed that was normal behaviour, lumpy cam maybe??? but anyway, after running the car on nothing but V-power the idle has suddenly dropped to around 750-800rpm and idles rock steady. Is this because of the assumed cleaning properties of Shell's finest, or is it some other kind of black magic?????

[Wigeon Incognito]

My theory with these things is that if you don't understand it but its positive, assume its witchcraft and get on with enjoying the sun.

[T5SOR]

Higher octane fuel, meaning the timing is slightly high (17-18 TDC) possibly. IIRC you have a 1.8 converted 1.6? Mine is the same, slightly lumpy idle. Retarded the timing and seems alot better. Might be an idea.
The cam angle sensor on the back (right hand side) just requires turning clockwise


Mike

[swansea v6]

Yes it is a converted 1.8, does this engine have a knock sensor? if not then this happy outcome is either due to voodoo or witchcraft........

[benjc]

swansea v6 said:

Yes it is a converted 1.8, does this engine have a knock sensor? if not then this happy outcome is either due to voodoo or witchcraft........

No it doesn't. If you have a minute you may want to clean the throttle body, that can sometimes help.

[T5SOR]

It has no knock sensor but, if your timing is advanced to more than 14 degrees it will run lean. If you add higher octane fuel then this will compensate. Then again, vodoo and witch craft sound more like it

[swansea v6]

Used some 10k boost on the throttle body today, plus another can of carb cleaner to thoroughly clean every thing I could!!!! also took out the plugs and poured a little redex cleaner down there.....what a difference, idle is now rock steady all the time and the engine just picks up so much crisper than before. Didn't really expect to much of a difference, but after seeing how much crap and crud there was, i have decided to do this every time i change the oil, WELL worth doing

[franv8]

As before - no knock sensor - early MX5 management pretty crude.

Timing has no effect on lean/rich mixture, but obviously over advance causes pinking, and higher octane fuel (V power) will delay the onset of this. 14 degrees is practicaly as far as you can go on an early 1.6, but don't know what it'll be for a 1.8... do check it from time to time, a single bolt is all that holds it in adjustment!

[nicecupoftea]

Apparently the timing advance mod does very little on the 1.8, a slight increase in low torque with a slight loss of top end power, but barely noticeable by all accounts - I decided not to do it.

TBH cooking unleaded is all I use in mine with the occasional tank of V-Power for detergents etc.

[T5SOR]

You have a normal 1.8 though! The poster has a 1.8 in a 1.6 car. So he has 1.6 coils, throttle body etc. It will run very different to yours

[nicecupoftea]

Sorry, missed that

[T5SOR]

nicecupoftea said:

Sorry, missed that

Thats ok Have you driven a 1.6?

[nicecupoftea]

No, just my dad's old UK 1.8 and my Jap 1.8.

[T5SOR]

nicecupoftea said:

No, just my dad's old UK 1.8 and my Jap 1.8.

How does the UK and Jap compare to you?

[nicecupoftea]

My dad got rid of his a couple of years ago so it's difficult to say really - do you mean in the engine & driving experience or in general?

I'd always go for the import as it's specced so much better, less likely to be rusty, lower miles, etc. Driving wise I think they're pretty similar. I think the UK car was more supple on UK roads but I have Bilstein shocks that make it a bit crashy...