OBD2 AAA stalling when cold, then running on five?

[bobda 0]

Nope, didn't sort it (didn't expect it to).

We need a well-running control vehicle to measure sensor readings against. Any takers?

[james4287 1]

do you have a K&N? i'm wondering if this is effecting maf readings when cold which is causing the over-fuelling? i will try original air box when i get a minute.

i've also replaced the plugs this week and am running it on optimax. alas, still the same.

another thought, i have a intermittantly dicky ignition switch? do you?

[james4287 1]

note: very bad this morning, suspect due to very cold ambiant temps today. sounded like it was running on four cylinders at idle, sounded ok at 1500 revs, but dropped down to idle it was on 4 cylnders, then five then six, after about 15 seconds it was fine. power was perfectly fine, though hesistation at approx 5krpm when cold still persists.

changed the coolant temp sensor yesterday aswell, hence why i "tested" this morning, alas no different.

also something else ive noticed is maybe a very slight missfire? when cold, i.e. if i place my hand between the front pannel and the inlet mannifold, when warm theres almost no movement at all of the engine, when cold theres a very slight amount of movement.

think compression test may be the way to go next.

[bobda 0]

No, I don't have an induction kit. Other than a K&N panel filter, it's completely standard and even before I fitted the panel filter, the problem was there.

Cleaning my throttle body has improved the running of the car a lot. It would appear that your problem is worse than mine, I get good running at idle on startup from col, but when I rev it in the first few minutes it cuts out then runs very rough or fails to start at all.

It's definitely related to overfuelling. Seeing as changing the coolant temp sensor hasn't affected yours, I am suspecting a MAF problem. Did you change both sensors (ECU and dash)?

[james4287 1]

i only have two sensers as far as i'm aware, ecu and fan. i've replaced the 2 pin blue sensor of the ecu as far as i know!

[patpong_pete 0]

if its not your coilpack would be poss to buy your old one that u replaced if its not cracked

thanks pete

[bobda 0]

i only have two sensers as far as i'm aware' date=' ecu and fan. i've replaced the 2 pin blue sensor of the ecu as far as i know!

[/quote']

The fan switch is attached to the rad, surely? Fan switches are usually totally independent of the engine running, to prevent overheating.

AFAIK, there are two sensors, one for the ECU and one for the dash.

[james4287 1]

ooooooooook may have to look under the bonnet a bit further now then.

have also noticed missfire/bad idling when hot aswell. very slight as in you can only hear it and feel a slight vibration through the steering wheel/gearstick. when driving it's un-noticable. only when you open the bonnet and rest your hand on the engine between the inlet and the front pannel you can feel the engine moving. where as usually it's almost totally still.

don't suppose anyone could confirm how they're vr6 is when stone cold and hot [fans cutting in]? - does the engine remain almost totally still with your hand resting between inlet and front pannel?

but with all new componants ignition side and power is excellent as always with no blue smoke i suspect compression is good which leaves a fuelling problem? faulty injector?

Pete, sorry chap but my old coil-pack is cracked.

thread which may be of interest.. http://www.vr6oc.com/e107_plugins/forum/forum_viewtopic.php?34096

UPDATE: probably a coincidence and will bear no relevence at all but i removed the airfilter & MAF tonight, drowned it in electrical cleaner, allowed it to dry off and took it for a spin. seems to idle better when warm now. - avoout 100oc oil temp on mfa.

[james4287 1]

UPDATE: fitted original air box and reset pcm, it's been a week now and idling hot & cold is fine, mpg has increased. the 3krpm problem has got better as in now it's 4krpm and it'll hesitate and drop to five but not stall.

[bobda 0]

OK - if yours has responded to a change in the air intake system, then I'd say the problem is either the MAF or the air intake temp sensor.

The temp sensor is obviously going to be the cheapest option to change.

It sounds like you've got your back to the stage mine is at.

[Seademon 0]

My cars done this since I've owned it! I've had it just over 3 years and its always been the same, I just let it warm up before I set off in it - I've done loads of ring trips & trackdays in it and never had a problem - my car has no fault codes or anything.

[bobda 0]

Mine has no fault codes any more after I cleaned the throttle body and it still does it. No fault codes will be logged if the readings are within an acceptable range. Personally, I think it's a combination of a couple of things - air intake temp sensor and MAF, which would explain why it only happens when cold.

[GVK 1]

Mine cuts out/misfires/stalls if you boot it when cold, as said much earlier in the thread, it's excess oil pressure holding open the lifters - if you boot it so it stalls it sounds like low or no! compression when cranking, running on 4-5 or less when restarted.

You get a pop/backfire because the valves are open when they shouldn't be

I just warm it up before booting it, like you should...

[GVK 1]

Ford had similar problem with their zetec engines when they were first introduced, they eventually had a modified PRV in the head to stop them doing it, and they recommended using 5w30 also.

[james4287 1]

maybe a swap to 5w/30 is an option worth trying out!

since i refitted the airbox and reset the ecu things have been marginaly better. until this week where i notice very lumpy idle when hot, i'm still suspicious about MAF but it's not bad enough to warrent changing as of yet.

[bobda 0]

I wonder. What type of oil are you on currently, 10w40?

Mine was run on Synta Gold 5w40 before I bought it but I don't know if the problem exisited before I bought it.

MAFs are £52+VAT for exchange at GSF...I'm considering it.

[bobda 0]

Right, having read all about oil grading, I'm going to switch to 5w30.

Will let you know how it seems...

[james4287 1]

any update?

[bobda 0]

I've not changed over yet!

[james4287 1]

Random thought, had the use of a vr6 sharan this week, did the exact same thing and came up with a mass air flow senser code, frustratingly the customer didn't want the senser replaced and said he would live with it.

but was the mass air flow the cause of the fualt we're all having ! ?

[Devildub_06 0]

I have just been reading this thread with some interest and have followed the work done. It is a very good theory that overly thick oil could potentially overprime the lifters, what I would be tempted to do if you have garage access would be to let the car cool right down, re-inact this problem and drag it back in immediately for a compression check. If the thought is thick oil in the lifters, you won't even make a kittens breath of compression.

With the Sharan you borrowed, the MAF error could be a result of the same problem, if the engine is partially holding valves open, then the lambda sensor will be seeing extra air being pushed out on the compression stroke and trying to fuel up accordingly. The MAF at this point will be effectively out of sync and would have thought it would create an error code accordingly. Did you reset the error code and see if it came back on the Sharan?

The "strong" smell of petrol as you try to restart suggests overfuelling and the fact that if left for a few minute then starts tells me that it's fuel evaporating into any air space it can get into, hence the rather meaty bang you get when it restarts.

Cheap and cheerful answer, change to a thin oil lol!! And obviously check leads etc for arcing (I know you've changed your coil pack and plugs at this point).

bobda, only consider a cheap MAF if there's decent warranty on it, i've heard some stories about the factors one's.

[james4287 1]

With the Sharan you borrowed' date=' the MAF error could be a result of the same problem, if the engine is partially holding valves open, then the lambda sensor will be seeing extra air being pushed out on the compression stroke and trying to fuel up accordingly. The MAF at this point will be effectively out of sync and would have thought it would create an error code accordingly. Did you reset the error code and see if it came back on the Sharan?

[/quote']

Interesting thought, having plugged my car into vagcom tonight i'm inclined to agree, i have 3 fault codes;

00525 - 02 senser implausible signal, senser, wiring etc,

00561 - fuel mixture control, fuel pump, pressure, mass air flow etc, and

00553 - mass air flow senser out of range

so if we think it's a mechanical problem such as valves sticking open then there will be excess fuel/air going into the cylinders straight down the exhaust, which may give the three above codes as the 02 senser is being drowned with fuel, mixture control because it's chucking loads of fuel down the exhaust and mass air flow because it's seeing totally different readings to what it thinks it should be compared to 02 readings?

I have this weekend changed to 5w/40 and have to say the problem is almost non existant now, will be re-fitting the K&N in the comming days though out of curosity!

[bobda 0]

5w40, I thought 5w30 was the recommended rating.

My yearly service is due in June so I'll be changing then.

In the mean time, I have learned not to boot it at cold!!

[bulldog 2]

My 97 highline with 78K and full VAG history does the same, my 96 highline I had last year with 126K and full history did it too. My mates Clio 182 does it also and recons it does this to protect the engine when cold.

My car will die if you boot it when only warmed for a few mins, if you drive 2 miles or so and boot it, it cuts down to 3 or 4 pots and runs really bad for the next mile.

I've got used to it so I let it warm up as if it was a turbo car, since then I've had no probs.

[Devildub_06 0]

No car would ever intentionally be made to misfire (with the exception of rev limiting), it would destroy the catalytic convertor! The clio 182 ECU is a little bit smarter than the VR6 one, but i'm pretty sure it doesn't have a cold rev limiter, the only car I can think od that does off the cuff is the new BMW M3 which sets rev limiting in stages from cold to hot.