Problem with 1.6 2003 Focus, with Warning Light!

[AL...Ease]

Hey up, my brother's 2003 Focus has been playing up for about 6 months, it all started when he let it run out of oil (not very mechanically minded), which resulted in some misfiring and the management light coming on.

Since then he's had it to a garage who have replaced the O2 sender, leads, plugs and flushed the engine, but it still isn't quite running properly at low revs. He hasn't noticed a performance difference above about 2,000RPM, but when it's warm the idle is erratic, going from 800 to 600 rpm and sounds a bit rough.

The exhaust pops on the overrun sometimes and, with the airbox off, I noticed a lot of quiet popping coming through the inlet, which I've not heard on a car before. I'm no expert, but I fear that it could be something as simple as needing a pro (Ford) ECU reset, or could be as serious as valve overlapping.

Can anybody lead me to what could be the problem? If it sounds like something the main dealer may be able to sort we'll be happy, but they're known for over-charging, hence the reason he hasn't taken it there yet, so fingers crossed it won't be too expensive.

Cheers for reading,


AL

[AL...Ease]

OK, so it's a head-off job, thanks for the info. The garage that he took it to wasn't a Ford specialist, just a friend-of-a-friend sort of garage.