VR6 MAF cleaning

[Andy T 0]

Yeah try disconnecting it (electrically) first, could also try bypassing it all together if you have some spare pipe or tube.

[Rpmayne 0]

I phoned VW earlier and told them that the symptoms have persisted and that I was suprised the test driver didn't notice any problems. It now turns out that the test driver didn't think all was well but thought it was better than when it came in and with no codes that was job done.

 

I went on to mention whether the ISV had been checked and after a lengthy pause I've got a free hour labour so its going back later in the week.

 

Will try the ISV tonight aswell to see whether it does make a difference.

[Rpmayne 0]

Tried unplugging the ISV tonight and drove around for abit. Although the MPG is still struggling to get into the 20's, the idling has never been better. Unplugged it didn't stall once, all but a few times going straight down to 700 and sticking there. What does that mean? Can't believe the difference, still something wrong with the MPG but so much more driveable.

[Andy T 0]

When its unplugged the shutter is permanenly open by a few mm, so I think the idle speed is purely controlled by the flow of air through that gap. Going down to 700 may of been due to other loads on the engine or because its not runnning properly, fuelling, ign timing etc.

 

Sounds like you need a new ISV then. There have been a few on ebay lately go for £20-ish, btw mk3 VR6's use the same ISV.

 

An emissions test would show up if the lambda is not doing its job?

[Rpmayne 0]

I started it from cold this morning to goto work with the ISV unplugged and it would not start, coughed and spluttered but would not idle. Plugged the ISV back in and it did idle.

 

On the way I tried depressing the clutch and it was trying to stall again. As a test, once I was at work I switched it off, uplugged the ISV and it restarted and idled as it was last night when hot. Looks temperature dependant somehow.

 

Cheers Andy, will get VW to have a look at the emissions later this week. You still recon the ISV is at fault? Guessing they'll be £100ish from VW so will look on ebay.

[RS VR6 0]

Have you tried another MAF? If the MAF is bad...no amount of cleaning is going to help. The MAF could be the problem...eliminate that probability by switching it from another Corrado. See if you can borrow one for a few days.

 

Mine was doing something similar last week. The idle would randomly "hunt" and when crusing, I can feel the engine sputtering. I switched to a spare MAF I had...and so far the issue hasn't returned.

 

Another thing that can cause strange idle issues is the ignition switch.

 

Check your fuel pump (see if you have consistant fuel pressure) and fuel filter. An extremely dirty fuel filter can cause sputtering issues.

 

Maybe the Crank Sensor....normally if thats bad...the car woun't even start.

[Andy T 0]

The ISV must still work to some degree if it improves idle at cold start, the air gap when unplugged might be unsufficient to maintain idle when cold. If you can get one very cheaply it would still be worth changing.

 

Any MOT garage could do an emissions test for you, I'd avoid VW they'll charge a fortune. Might be worth getting the test done from cold so you can see what the emissions are like before the lambda warms up and takes effect, during engine warmup, and when hot.

 

Have you tried running the car with the lambda unplugged? If it runs well with almost normal MPG, it must be an issue with the lambda probe, its wiring or earth through the engine block. On my G60 I ran an extra earth wire from lambda plug to a point on the chassis.

[Rpmayne 0]

RS VR6, I haven't been able to try another MAF. I was going to borrow the MAF off a mates Golf VR6 but it was a 4-pin type and mines a 6-pin. To be honest I was hoping VW could positively tell me that was the problem as its alot of money, but alas the lambda was all the computer would tell them. Not to say that isn't the cause obviously.

 

How would the ignition switch cause problems? I changed both the crank sensor and ignition switch about 2 years ago but I've got the fusebox exposed at the moment so can check things easily. I also bought a fuel filter but don't think I ever fitted it so will try and find that.

 

Andy T, only reason I would get VW to do it is that they owe me 1 hours labour free. I think I tried unplugging the lambda before but will try again tonight now its got a proper connector on it and see what happens.

[Rpmayne 0]

Right, just an update on a few things you've suggested. Cheers for the help:

 

ISV plugged in when cold - Original problems; poor idle, occassional stalling, sometimes hesitant and poor MPG (16 max v.careful driving).

ISV unplugged when cold - Will fire but not start.

 

ISV plugged in when hot - Original problems; poor idle, occassional stalling, sometimes hesitant and poor MPG (16 max v.careful driving).

ISV unplugged when hot - Problems improved but not perfect; better idle, no stalling but still poor MPG.

 

Lambda unplugged - No noticeable difference plugged in or unplugged.

 

MAF unplugged - Idle becomes progressively irratic until it stalls.

 

Although the above seems to suggest a problem with lambda primarily (changed about 3 months ago) and the ISV, is it feasable that the MAF could be giving duff information but not out of range so VAG-COM shows no errors and the lambda is incapable of sorting the problems out??

[RS VR6 0]

The MAF will not always throw a code when bad.

 

A faulty igniton switch in my Golf caused an erratic idle when it went bad. Over time and hundreds of times it was cranked to start the car, the terminals will become worn and have poor contact with the ignition. Since you said it got replaced...you can probably rule that out.

 

From the bad O2's that I've seen...it just causes the car to run rich.

 

The easiest way to rule out the guesswork, is to get your hands on another ISV and MAF. Try one then the other.

 

The car should idle (roughly) with the ISV unplugged...well at least mine did. :drinking:

 

Also try unplugging the Throttle Position Sensor (Plug on the TB). The car should still idle...if the MAF is bad...the car should stall (not 100% sure though).

[Andy T 0]

Another thought, reading back over your post about your sooty exhaust, and my own previous problems with my g60, i'm convinced that either -

 

The lambda wiring is damaged/wrongly connected/badly earthed, connector pins are corroded(water can get into these connectors)

 

OR -

 

The lambda probe is goosed, possibly due to bad wiring/short circuit due to water in connector.

 

You could do with an auto electrician checking the lambda circuit for faults, and checking voltages/resistance on the connector with ignition on.

[Rpmayne 0]

Just a progress update. Took the VR over to VW on wednesday night and heard back yesterday that they have found the problems. Apparently there was an air leak on the intake pipe somewhere because a 'clip' was missing, not sure what that actually was yet. And the more annoying fault was a faulty spark plug on no.1 cylinder, I had replaced the plugs about 3 months ago when I did the coil pack ordered from GSF. Wouldn't have thought to go over them again. They've replaced them free of charge because I had to go back again which is good.

 

They took it for a test drive checking the MPG and round town it shot straight upto 25mpg, pretty good for a VR so hopefully all problems sorted.

 

Thanks for all the help, I'll try and ask them where this 'clip' was and post incase anyone else is having the same probs.

[CazzaVR 0]

Rpmayne, any update on this? Where was the clip?

 

Cheers

[gg7aph 0]

Yeah - where's the clip? I'm seeing a lot of people cure similar sounding problems to this through finding a leaky air hose...could this be my problem too?

my VR6 suffers from hesitancy pull-away and low tickover/hunting. I've cleaned ISV and MAF, changed plugs, leads, fuel filter, air filter and oil filter.

[GreenRado 10]

Sorry to awaken an old thread, but my MAF was causing a worse an worse idle. It got to the point where she was just cutting out on cold starts/cold days. Was getting code 533 on VCDS.

Took the MAF apart and cleaned with Carb/Intake cleaner and all symptoms are gone! Now idling superbly.