Low idle speed after battery disconnected

[YarisTR-VVT]

Hi all,

I've had my 2009 Yaris VVTi from new and have never had any issues with it, until it went in for a recall to have the airbag replaced and the battery was disconnected.

Now, on a cold start the idle speed is much lower than it used to be and the engine almost stalls. The idle speed on cold start used to be about 1000rpm but now it fluctuates between 500 and 800 rpm. Touching the accelerator to increase the revs to 1000rpm stops it stalling and after driving for a few minutes the idle speed is fine and the car runs as before.

Took it back to the dealer who kept the car overnight and said they saw the cold start issue but there are no faults showing on the ecu so there's nothing they can do!

Have seen a few posts about this type of problem clearing after a couple of days, or after a long drive. But it's been 7 days now and I had a 200 mile round trip one day last week but I still get the problem on a cold start.

Any suggestions?

Thanks.