2003 Mk2.5 1.8iS Cold Start Issue

[GadgeS3C]

Over the last few weeks my 1.8S has struggled a little on starting. Seems to be worse on cold days. Once it fires up tickover moves up and down between approx 1,700 & 1,200rpm. If I drive off it will struggle to rev and coughs occasionally.

Once it's done a few hundred yards it's usually fine.

Any suggestions where to start looking. Idle speed control or more likely a cold start system?

Thanks!

[GadgeS3C]

Bump - any suggestions?

[Rickyy]

Just thinking out loud with no experience of this problem, but I'd be looking at whatever tells the ECU that the engine is cold, coolant temperature sensor maybe?

I've heard of cars having hot start problems because of this, so I guess the reverse could happen I suppose.

[GadgeS3C]

Thanks - that was pretty much my thought. It only happens from cold so I wondered if there is a specific "extra" cold function somewhere.

Lack of response suggests it's not that common so I guess I'll be getting the manual out and fiddling.

[MX-5 Lazza]

Could be the engine temp sensor on the back of the block. They can die so that they always give a hot signal or cold signal.
It could also be CAS, coil pack, AFM or a number of other things.

However, you say the idle is high and jumps around so it could just be a gummed up idle control valve. That's where I'd start, strip it out and clean it and the air channels it uses with carb cleaner. I'd do the throttle body while I'm in there.