Technical Uno Turbo Mk 1 choke issue?

[PerfectV]

I have a 1989 Uno Turbo Mk 1 that has developed a weird issue on cold start up.

Issue is that it will idle fine with the choke working for about 2 minutes but after that it's like the choke is cutting out and it will stall if you come to a standstill and don't give it a little bit of accelerator. Once it gets up to temp its fine and drives as normal. There are no odd sounds or anything like that, just cuts out.

Any ideas? I was thinking possibly the O2 sensor might be fouled?

 

[alexGS]

Welcome to the forum... yet another Kiwi

As you're probably aware, there isn't a 'choke' on a fuel injection system. A choke is the term for a mechanism that closes a flap across a carburettor intake, to restrict airflow and therefore enrich the mixture. The mechanism also adjusts the throttle plate stop to raise the idle speed.

On the Uno Turbo, there is an Auxiliary Air Valve bolted to the cylinder head near the distributor. It is a rotating-valve design that uses a bimetal spring and a heating wire. The valve is plumbed into the intake air in such a way that it bypasses the throttle plate, raising the engine idle speed. The idea is that as the engine warms up, the conduction of heat to the air valve closes it. Alternatively, the electric current to the heating wire also closes it.

The system is obviously very approximate and if it closes too early (as it sounds like yours is), it's worth trying another valve (it may also be adjustable by means of a screw in the valve). This is a fairly common Bosch part that turns up on other LH-Jetronic cars of a similar age. I got one off another FIAT engine when I had the same problem with mine (engine dying during warm-up).

Mixture enrichment is another story entirely and is performed by the ECU according to the coolant temperature sensor (on the thermostat housing). If the mixture is wrong, the engine will be difficult to start when cold, or idling rough when hot. I doubt you're having either of these problems. Also I don't think you have an O2 sensor on a NZ-market Uno Turbo Mk1 without catalytic convertor. Well, I don't have one on mine, anyway

-Alex