Another Idle/ Rev Issue (yes i have searched lol)

[meta]

Hi everyone,

Got another idle issue with my mx5...I'm starting to loath this now...

So this is my problem:

The engine is idling poorly, it tends to drop down from say 750 to like 250 at times, in traffic, i find myself holding the accelerator to keep the revs up, it dips intermediately and often fluctuates randomly, from the outside, whilst it is idling it sounds like its struggling to breathe, its not a smooth consistent sound, its struggling sound, not a smooth note.
The car however, once driving is perfect, it doesn't struggle and there's no lack of power or response from the throttle, only at idle it has these issues.

Problem solving lol:

The mx5 has recently had an engine swap about a month ago, along with that, i've also replaced the AFM, i've adjusted the idle speed and now the engine is revving way to high, around 1600rpm at operating temp, however, after say 30 seconds, it drops to around 750rpm and sounds sickly again?

I've cleaned out the throttle body, AFM and the injectors have also been serviced

Considering the new engine, everything is good, compression is fine, the temp coolant switches both front and back are fine to, aside from faulty wiring and the possibility of something wrong with the afm or throttle body, i can't pick the problem of why it won't hold idle?

If anyone has an idea of what i could be, it'd be greatly appreciated

Thanks Meta

[StanTheMan]

I'd check the O2 sensor

[Charlie Brown]

Try this: http://www.miata.net/garage/isc.html

My NA had the problem that when ever it came to a stop the idle would drop from 850rpm to around 300, come up and drop again, sometimes stalling.
I cleaned the idle control valve and the problem disappeared.

[bruce]

My favourite - Spark Plug Leads!

[meta]

hi all,

thanks for the replies, the idle control valve might be a go, thanks for the link charlie

As for the leads, sorry, new leads and plugs

O2 sensor, i'll check that out also

I have to wonder if the ECU is a drama? i'd imagine they'd be no difference being the engines are literally the same?

Thanks meta

[93_Clubman]

I have to wonder if the ECU is a drama? i'd imagine they'd be no difference being the engines are literally the same?

Assuming you've gone from one standard NA6 B6 to another standard NA6 B6 engine then ECU won't automatically be a problem. However, the occasional problem has occurred with NA ECU earthing & components on the NA ECU PCB.

[fattima]

You mention that the engine was replaced, is the engine earthed OK? Just on the off chance that it is getting a better ground when given a rev.

[GP]

Assuming you've gone from one standard NA6 B6 to another standard NA6 B6 engine then ECU won't automatically be a problem. However, the occasional problem has occurred with NA ECU earthing & components on the NA ECU PCB.

Could anyone convert this to english?
I've also been trying to diagnose this

[93_Clubman]

Assuming you've gone from one standard NA6 B6 to another standard NA6 B6 engine then ECU won't automatically be a problem. However, the occasional problem has occurred with NA ECU earthing & components on the NA ECU PCB.

Could anyone convert this to english?
I've also been trying to diagnose this

PCB = printed circuit board - basically, given factory specs for the values of the components on the PCB aren't available, it's difficult to repair the ECU, although I believe if it's an ECU earth post it can be repaired. Ideally, borrow a good NA6 ECU to troubleshoot.

[GP]

[93_Clubman]

:shock:

And perhaps a Bex & a lie down for the owner?

[GP]

Well thanks for nothing

[93_Clubman]

Well thanks for nothing

Perhaps start your own thread & be more specific about your car's problem, or ask specific questions.