rough idle 156 V6

[poohbah]

Apologies if this has been discussed previously (I couldn't find anything specific), but I am just looking for pointers.

My '99 156 V6 Q-auto has been running perfectly (major service 2 months ago including belt/pump change ... $$$$). But yesterday, after being in stop-start traffic for about an hour, and sitting stationary at a traffic light  it started idling slightly roughly.

Normally it idles very evenly, sitting bang on the 800-900 rpm mark, but it just became a bit lumpy, dropping down to 600-700rpm. Under load and driving normally all seems normal. It also seemed to be only if the transmission is in gear - when I shifted it to neutral it idled normally again.

On the drive home from work, it was generally similar, though maybe a little less pronounced - a little rough on idle, but fine when driving.

No problem starting and not running hot. Initial check under bonnet while running showed no obvious issues, vacuum leaks, loose leads etc, though on listening closely, it sounded like a faint set of "electric" clicks (maybe 3-5) would occur every now and then (possible misfire, coil packs?)

It seems pretty minor, but you soon get to know when something doesn't feel exactly right. Haven't driven yet today, so no idea if it is one of those weird temporary bugs that sometimes just disappear.

[bazzbazz]

Have you scanned it with diagnostics yet?

[poohbah]

No bazz, I don't have a scanner. No warning lights on dash or anything.

[bonno]

Hi Poohbah
Further to BazzBazz comment, it sounds like it could be a coil pack is on its way out or a faulty spark plug. I assume the NO engine light when running normal, however did you notice it light up when the rough idle occurred. If this occurs then to identify which coil pack or spark plug is at fault please refer to the following link on a similar issue I had with my 156 JTS and how I diagnosed the problem using a cheap hand held diagnostic scanner.
http://www.alfaclubvic.org.au/forum/index.php?topic=2380.msg108161#msg108161

[poohbah]

Cheers Bonno - all the warning lights come on briefly an as normal when you start her up, then go off. No warning light at all while running. I just started her and had another close look, and its as reported before. Still lumpy when in gear but idling, and intermittent electric click coming from near the first two connections/plugs on the left front side of engine. (circled - can't tell which)

[poohbah]

So possible injector fault, given that's where the click is coming from?

[poohbah]

Well, that's weird.

Poked and prodded around the connectors to the first two injectors a little bit, and replaced the insulation tape you can see in the pic. (The tape doesn't appear to do anything of note other than tidy things up a bit - certainly no exposed wiring or anything like that. And the tape has been there since I've owned the car - so plus 4 years).

Maybe a coincidence, but all now appears normal. No rough idle, in gear or neutral, and no intermittent click.

I guess it could be a wire/connector on the way out, which my poking jiggled back into a better contact position.

Will see how it goes, and whether it resurfaces. I'm planning to drop into the workshop when I get back from interstate in a couple of weeks to see about fitting a replacement AC compressor I bought, so will mention it then.

[bazzbazz]

Just so you know, that loose wire you have going round the left side (as in the photo) of the coil cover is supposed to go under the cover and through a hole at the bottom of the cover.

Nothing to do with your issue or its solution, just like to be tidy and do things the way they are supposed to be.

Yes, I know, picky, picky, picky. 

[poohbah]

It actually now looks like this.

Anyway, main thing is that it all still seems to be working properly. Bazz, could the (currently-absent) intermittent clicking have been an injector firing erratically?

[bazzbazz]

The clicking would more likely been the zapping sound of a coil shorting out.

[poohbah]

odd that it stopped then.

[bonno]

The fault only occurs when engine has been running hot or in stop start traffic. Need to replicate same condition to see if rough idle returns.

[poohbah]

cheers fellas, and good tip sportiva.

I will see how she runs in peak hour tomorrow, though it was actually misbehaving from a cold start on the return drive home the day it started and on the weekend before I prodded and poked around the injector connectors. Since then no issues during a couple of 30 min runs, though admittedly I haven't been stuck in traffic for any extended period.

[Beatle]

If you intend washing down the engine, remove the coil packs first.  Water will get into the sparkplug tubes so best to pull it all apart beforehand to make it easier to degrease, clean and de-water.

My V6 has a distinct erratic hard miss at idle, but last time I filled with 98 in lieu of the usual 95 and it's made a distinct difference to the idle.  Can't say I've noticed any change in performance off idle though.

[bazzbazz]

If you intend washing down the engine, remove the coil packs first.  Water will get into the sparkplug tubes so best to pull it all apart beforehand to make it easier to degrease, clean and de-water.

Or cover the top of the camshaft covers with plastic & tape and then do that area individually by hand. Just a thought.