VR6 ISV - should it click/buzz?

[Andy T 0]

Done the search and checked the Wiki, should the VR6 ISV click/buzz/vibrate when the ignition is turned on? mine doesn't make any noise or vibrate noticibly.

 

My idle tends to dip very low then rise high a few times when cold, when warmed up it is stable but not very smooth (vibration in car) this gets much worse when headlights/heated screen or seats are turned on. The ISV doesn't seem to react to these loads, the rpm needle stays in the same position - is this normal? Our mk4 polo idle tends to re-adjust itself when electrical loads are turned on.

 

I've cleaned the ISV with carb cleaner (wasn't that dirty and moved freely) What else affects the workings of the ISV, does the throttle position sensor tell it when to operate?

 

Cheers.

[Son of a Beesting 0]

Doesnt appear to be anything to worry about mate.

[Andy T 0]

I can live with it being erratic when cold, its just the constant vibration through the seat & steering wheel that's annoying.

[Andy T 0]

Somebody must know the answer to this, or understand how it works?

[Crasher 3]

Have you had a fault code read?

[Andy T 0]

Yeah a few weeks ago, no fault codes (except one for ABS) and everything else looked fine on VAGCOM.

[dr_mat 0]

Sounds more like a slight misfire at idle to me.

The revs shouldn't change when you add electrical load, in fact the fact that they *don't* is testament to the ISV working properly. Small engines have to work harder to counteract the extra force required to turn the alternator. The VR6 barely notices.

[craigowl 0]

Something not right. Sounds like it is faltering.

Cold and warm idles should be smooth IMO.

Mine idles perfectly smoothly at about 750-780rpm when warmed up and with no vibration.

 

One of my favourites for missing VR6s - How old is coil pack?

[Andy T 0]

Sounds more like a slight misfire at idle to me.

The revs shouldn't change when you add electrical load, in fact the fact that they *don't* is testament to the ISV working properly. Small engines have to work harder to counteract the extra force required to turn the alternator. The VR6 barely notices.

 

That makes alot of sense, so I can eliminate the ISV for now. During the first five minutes of warmup, it idles at around 850-900 rpm which is very smooth even with loads on. After five minutes the idle drops to the usual 650 rpm and thats when it's rough.

 

The coilpack is the original as far as I know, I have checked it for arcing at night with a plant mister, no arcing occurred, is it still worth replacing anyway?

[craigowl 0]

Personally, I would seriously consider coilpack as a problem.

My car was running fine with original at 10 years old when I bought it, but I am almost never out in it in damp or wet weather.

 

I read about coil pack problems on forums. (Due to great heat from engine block onto which coilpack is bolted, plastic part(s) eventually crack. It can then behave just as a cracked bakelite distributor cover used to - arcing, missing etc.)

 

I sprayed pack with mister and engine started to falter.

 

Took coilpack off and on VERY CLOSE examination you could see a few hairline cracks in the plastic. I am certain the original component will not be 100% sound on your 1996 Corrado, but could not guarantee that this is definitely the one and only problem with your car.

 

I have replaced, or attended to, a few parts on the C that are regarded as likely weak spots after 10 years.

 

Apart from coil pack, typically they are:

 

top hose (I replaced most hoses with Samcos)

 

driver door handle (had to when it failed! - they all seem to)

 

headlight switch (when it failed - extremely common - feel the heat in it when you have had lights on for a few minutes - pathetic design IMO)

 

serpentine belt

 

heater matrix

 

flexible brake hoses

 

some brake pipes (at an MOT)

 

fuel filter (has yours ever been done? - sometimes left out of services)

 

auxiliary water pump

 

Oh, and original solitude alloys had to be refurbished as they were oozing air at tyre rims. Annoying, very slow leaks eliminated.

 

Have not done timing chains and a few other things peeps on here likely to include.

[dr_mat 0]

The coilpack is the original as far as I know, I have checked it for arcing at night with a plant mister, no arcing occurred, is it still worth replacing anyway?

 

If it sounds like it's misfiring, it's easy to find out .. A competent garage will be able to tell you if you have good spark on all six in ten minutes flat, and then you'll know, won't you..!

You can even buy spark testers at halfords et al. (Or just take the plugs out and look for spark yourself, if you know what you're doing.)

[Andy T 0]

I bought some of those spark plug testers a while back and have never used them, I thought they might be too far down in the head to see on the VR6. A few people have mentioned that checking for a misfire by watching a plug fire against the manifold is very difficult.

 

I might well change the coilpack as it's going to become a problem at some point if not already, should I go for genuine or are ECP/GSF units the same quality?

 

cheers.

[CrazyDave 0]

As above, sounds like coilpack.

 

I've been looking very closely at VR6 idling recently, the ISV has a pretty constant cycle when at idle speed. Depending on the engine temperature, the ISV duty cycle will sit at about 42% approx (in VAG-COM).

 

Fine stability and rapid loading of the engine (electrical loads, AC etc) is done with ignition timing. It adjusts so fast that the idle should hardly dip at all.

 

If you hook up a timing light, you can see it working at idle.

 

So if you've got a dodgy coil pack or leads the idle will be very unpredictable.

[Andy T 0]

Forgot to mention, the plug leads are about 2.5-3 years old (genuine VAG) no signs of arcing when wet, any other ways of testing them?

 

Crazy dave, if I was to borrow a timing light with inductive pickup, would I see any signs of misfires across each each cylinder by watching the light, or would it be happening too fast?

[CrazyDave 0]

Would be a bit fast, but you could get the general idea on no.1 and 6. The other cylinders would not have timing marks on the flywheel though.

 

Best bet is to try and loosen all the plug leads and lift them off one by one and listen to the engine, no change = bag lead / pack. I have never tried this on a VR before though so it may be a real pain to try and do.

 

I'd take all the leads off and have a good look at the insulation. Any nicks or cuts bin them and get a new set.

 

I have had a go a repairing my coil pack with high chrona laquer but it only lasted 6 months so I bit the bullet and went for a new pack. Ran much better than it ever had.

[RS VR6 0]

Check the voltage on your alternator? You may have bad or corroded grounds...check them too.

 

The ISV clicked when I did the output tests on my Vag Com.

[Andy T 0]

Check the voltage on your alternator? You may have bad or corroded grounds...check them too.

 

The ISV clicked when I did the output tests on my Vag Com.

 

Will try that, should the voltage across the battery terminals be the same or is some voltage drop allowable?

 

Will check earth cables too.

[Andy T 0]

Yesterday I tested the voltage between battery & engine block with engine running but no electrical loads, got around 14.3v. With all the loads switched on (Fogs, heaters, seats, headlights etc.) the voltage dropped to around 13.6v - is this normal? More worrying though was the engine note with all those loads switched on, it sounded rough and quite 'chuggy' as if it was starved of air, and engine movement was noticeable. I unplugged the ISV and it instantly ran smoothly, although the revs had risen to around 800-850 rpm. Does this mean the ISV is faulty? (It has been cleaned recently)