Lumpy low Idle

[cjm]

What are the main causes of an uneven idle and trying to stall when you pull up to a junction? The car (S2 111s) was misbehaving on the way home tonight, maybe it doesn't enjoy the cold!

[BiggestNizzy]

battery ?

[cjm]

I did wonder if it was the battery, it did struggle a bit to starting this morning. It was a new battery two years ago the car has sat for a few months over the last couple of years but has been running fine recently.

[robin]

The IACV is often linked to those two symptoms, as is inlet manifold vacuum leak.

Cheers,
Robin

[cjm]

What does the IACV do and how do I check it?

Edit - ok found here. I'll have a check and give it a clean and see how it goes.

http://wiki.seloc.org/a/Idle_Air_Control_Valve

[cjm]

New battery fitted and car is fixed, back to running great and all is good... apart from some *&^% reversing into the front clam and cracking the paint!!!

[robin]

Are you sure, in that case, that the alternator is working OK? Normally once the car is started, the alternator produces the current to run the electrics and some spare to recharge the battery; if replacing battery fixed your problem, either the old one was goosed enough to prevent the alternator from reaching normal running voltage OR the alternator is pants and you're supplementing it with your new battery charge, soon to get back to the original problem.

Did you fit a new battery based on any tests (e.g. somebody checking battery voltage when off/cranking/running)?

Cheers,
Robin

[cjm]

The AA came out this morning as it wouldn't start, he jumped it with a booster and ran it for ten mins. I think it was getting 13.9v with the engine running so the alternator should be ok, I can't remember what amps the battery was drawing during the time but it was way down on what it should have been. The AA guy then ran a test on the battery which said it should be replaced.
The battery was last replaced just over two years ago by AA so they fitted a new one for free. I'll see how it behaves on the way home and check the voltage, off and charging, etc once home.

[robin]

With a fully charged battery (or a battery not taking a charge) I would expect to reach 14.3-14.5 volts at the battery terminals. 13.9 volts is barely enough to force a charge into the battery.

I wonder if you have a corroded earth cable/earth post somewhere that is creating a voltage drop during charging ...

Cheers,
Robin

[cjm]

Checked the voltage again, with the engine off 12.9v, with it runing 13.6v and with all the ligths and fans on 13.2v. Thoughts?

[robin]

Might be fine if it's idling - can you get somebody to hold 2,500 RPM while you measure it, then you'll know for sure. High 13's at the battery probably OK.

Cheers,
Robin

[cjm]

Just hecked again and it was 14.1v running and 13.8v with the lights and fan on, so seems ok.

[robin]