2.5T high idle and erratic power
 

Not used car for a week and battery was flat so recharged it and on starting instead of the usual initial high idle and drop to about 7-800 rpm it stays at about 1300-1400 and driving it is rather weird as it seems to be surging a bit. Putting the aircon on high brings it more into normal.

Any ideas what might be wrong before I take it for code read etc.?

it's a 2005 2.5T with about 105,000 miles on the clock. Engine has always been faultless.

How old is this battery which died due to a week off?

Knowing the battery is in good shape and fully charged and knowing the ETM and MAF are clean is where I'd start.

Obviously there are many things it could be, but on past experience I'm guessing MAF. That would normally trigger a warning light, but you could always test by unplugging the MAF and seeing if there's any significant difference in behaviour.

I've had codes read (thanks Alex) and the key one is obviously the idle speed control - signal too high.

Now what happened next - Alex cleared the codes and then I tried to restart the car but the battery had gone flat, so we started it from his Volvo. Lo and behold on driving home the idle was normal and has stayed so.

So either it was some magic with Vida, the flat battery, or a combination that has so far fixed it...

Nothing usually simple with these cars.

https://i.ibb.co/9ZghRC4/marc.png


https://i.ibb.co/xfByydC/marc.jpg

Weak batteries can play havoc with electrical systems.

Personaly, if a battery goes on me, its swapped out and replaced with a Bosch S5 immediately.

Battery is only about 15 months old and is a Volvo OEM one and was fine until recently. I think there's a parasitic drain but I haven't found it yet. It's not the alarm siren battery gone bad as I've removed the fuse.