Rough idle <800 rpm when hot - 07 C30 T5 auto Topic is solved

[scot850]

The car that keeps giving!!

So after a lot of testing, wire repairs, all the grounds cleaned, the owner brought a brand new battery. I installed it and put it on trickle charge over night. On removing the charger it is registering 12.6V after sitting a few hours. Checked the alternator with the electrical system with minimal loading (heating off, radio off and DRL's only). Battery showed a 14.6V charging voltage which I consider normal.

I started the car and no warning lights, and car idled nicely. Took the car for a gentle 10km run around the neighborhood and then a couple of harder pulls on the highway to see if I could get any codes. Car ran fine, but has a whine. I'm guessing the turbo, but it could be the alternator possibly? I have read of that happening on P1's where the alternator seems to run hot.

On returning home, all seemed ok, until I started to back into the garage. Then the car started running a little lumpy, and the idle dropped a bit below 800 rpm. Rev'd the engine and it rev's well and cleanly, but then drops back to a low idle.

Can anyone suggest where to look?

Perhaps I should check the charging levels when the car is hot and see if maybe the alternator is going bad.

I changed the battery as the old one had been overheated following a mechanic leaving the main engine ground being left off. It is possible it has caused damage elsewhere?

Thanks,

Neil.

[scot850]

I've linked this to another thread on the follow on from this thread:

viewtopic.php?t=106623

Neil.