Throttle damper

[Roger Blassberg 0]

I have just done Basic Settings after a battery disconnect, cleaned out the ISV, checked the MAF and also for vacuum leaks. All seem ok, and yet the car

(VR6) regularly stalls, particularly if there is a high alternator demand and almost always when I dip the clutch after a period of closed throttle running such as going slowly downhill in traffic.

 

The throttle damper seems to be in the right place, but investigation reveals that it is not actually doing any damping - there is no noticeable resistance to the piston being pushed in. Is this a common problem, indeed is it a likely case of the engine stalling in the circumstances described?

 

Best wishes

 

RB

[fla 9]

could be - the throttle will likely be snapping shut, although this is slightly contradicted by your comment that it happens when its already closed. Have you checked the angle of movement via VAGCOM? Should be around 13degrees iirc. You could try winding the damper up a little but if there's absolutely no resistance, then its shot.

 

I found that relubing the ISV every so often helped this immensely - although knowing how particular you are, i'm sure you do this anyway!

 

btw, have you cleaned out the TB itself? Both sides of the butterfly?

[CazzaVR 0]

Have you checked that all the ISV pipework is completely clear?

[Kevin Bacon 5]

Very common. When the ECU switches from the over-run to the idling map and the conditions to allow a good idle aren't there, it will just fall on it's face.

 

The dashpot (aka "stall catcher") is quite crucial on the VR6 and does need to 'catch' the falling throttle blade as soon as possible.

 

Although I have to say, my money's on the MAF. Said fuelling conditions coming out the overrun map clearly aren't right and it's usually always MAF related, when everything else is OK.

 

I spent many years chasing this and it ultimately led me to Mr OBD2's door for a permanent solution.

[Roger Blassberg 0]

Thanks for all responses.

Could someone explain how the ISV works please?

What do I need to do to check the MAF, other than the "pull the plug off and see if it idles worse and then dies" (which it does incidentally)?

What do I do to convert to OBD2?

 

Best wishes

 

RB

[Kevin Bacon 5]

OBD2 is a very meaty conversion and there's a wiki guide on it. Essentially it involves retrofitting the intake, throttle, loom and ECU from a very late Golf VR6. Instead of an idle valve, OBD2 moves the throttle plate to maintain idle speed instead, which is significantly more stable.

It also uses a more reliable MAF, a better, faster ECU and much better software.

 

ISVs work by bleeding air past the closed throttle plate. The ISV engages when the ECU sees a throttle angle of less than 14 degress as per Fla. Do you have VAG com? CazzaVR's point about the ISV damper pot is a good one. It contains a noise dampening foam that usually ends up being blown through the ISV when the engine backfires, which block it.

 

The MAF pulling test is a grey area. The assumption is if you unplug it and the engine remains running, the ECU has bypassed it and is using the throttle sensor instead, but it's not as simple as that. If the MAF is pulled during warmup, the fuelling is so rich, it might keep running anyway, and if it's pulled when hot when the fuel metering is a lot finer, it will stall easier. Some ECUs seem to need the electrical connection of the MAF just being there though, regardless of what signal is coming out of it.

 

As a basic test, you can put a meter across gnd and the MAF signal wire (the red one IIRC) and it should show about 1V at idle. As you increase the revs, you should see a corresponding rise in MAF voltage, to a maximum of 4.5.

Edited January 16, 2012 by Kevin Bacon

[P3rks 11]

OBD2 is a very meaty conversion and there's a wiki guide on it. Essentially it involves retrofitting the intake, throttle, loom and ECU from a very late Golf VR6. Instead of an idle valve, OBD2 moves the throttle plate to maintain idle speed instead, which is significantly more stable.

It also uses a more reliable MAF, a better, faster ECU and much better software.

 

ISVs work by bleeding air past the closed throttle plate. The ISV engages when the ECU sees a throttle angle of less than 14 degress as per Fla. Do you have VAG com? CazzaVR's point about the ISV damper pot is a good one. It contains a noise dampening foam that usually ends up being blown through the ISV when the engine backfires, which block it.

 

The MAF pulling test is a grey area. The assumption is if you unplug it and the engine remains running, the ECU has bypassed it and is using the throttle sensor instead, but it's not as simple as that. If the MAF is pulled during warmup, the fuelling is so rich, it might keep running anyway, and if it's pulled when hot when the fuel metering is a lot finer, it will stall easier. Some ECUs seem to need the electrical connection of the MAF just being there though, regardless of what signal is coming out of it.

 

As a basic test, you can put a meter across gnd and the MAF signal wire (the red one IIRC) and it should show about 1V at idle. As you increase the revs, you should see a corresponding rise in MAF voltage, to a maximum of 4.5.

 

just to question on this..

 

Will the ECU need remapping, coming from a 2.8 to a 2.9?

[Roger Blassberg 0]

I looked for the OBD2 conversion article in the Wiki, but couldn't see it.

 

Are the necessary parts fairly widely available second hand?

 

Hasan, do you have Vagcom or some other means of measuring the throttle plate angle?

 

I'll replace the damper/dashpot, lubricate the ISV (which I hadn't done after cleaning it out), look again at the throttle body including replacing the gaskets, check voltages at the MAF and take it from there.

 

Regards and thanks for all advice.

 

RB

[fla 9]

yes, lets sort out a time to meet up. My laptop needs mains power unfortunately as the battery has died. Otherwise, we could probably have scanned it in the KBR carpark!

[Roger Blassberg 0]

Thanks Hasan,

I'll call you some time today. I have free time over the weekend.

 

I have now found the OBD2 article lurking in the archives. It looks rather daunting.........

 

Best wishes

 

RB

[Kevin Bacon 5]

just to question on this..

 

Will the ECU need remapping, coming from a 2.8 to a 2.9?

 

Nope. The tiny amount more cc over a 2.8 doesn't trouble OBD2 at all. I ran OBD2 on my 2.9 and it was spot on!

[Roger Blassberg 0]

I have now changed the dashpot throttle damper, which makes gearchanges much smoother as the revs drop much more slowly in the "in between" time. Hasan and I checked the throttle potentiometer sender and that looks ok (thanks for your time this morning, Hasan, good to see you again !!). We also checked the ISV, again no problems.

 

So it does look like the dear old MAF. Incidentally, Im getting the faintest hint of pinking on hard acceleration, even on Tesco 99Octane, using standard NGK plugs. So maybe the mixture is a fraction lean- may also point to MAF?

 

Best wishes

 

RB

[Kevin Bacon 5]

Does the pinking occur when the throttle is hard down, or just before it gets past 4000rpm and / or 75% load?

 

The lambda could be maxing out filling in the missing fuel the MAF is supposed to provide, in which case, yep, pinking would be the result.

 

Were there any "adaptation: Control limit exceeded - Lambda" type errors in VAG-COM?

[Roger Blassberg 0]

All Hail the omniscient Hayrick !! Different MAF, different behaviour.

 

So far, after a day of running with a different MAF, (found lurking in the back of my garage from a few years ago), the car hasn't stalled once even in circumstances which would have definitely provoked such behaviour before the swap

 

Still very light pinking if floored at 3000rpm. I don't think there were any messages on VAGCOM ( Hasan - didn't it read "No Faults" ?).

 

Much, much improved and generally a smoother-running engine when idling and slow running through traffic.

 

Thanks all

 

RB

[fla 9]

good to hear Roger! Yes we cleared the faults and none returned. Might be worth scanning again after a good drive though.