Harsh Decelleration

[Storm Warning 0]

Hi,

 

I have had a small problem on my storm since the day I got it but always assumed it was just one of those things. Today I decided to post about it here to set my mind at rest...or not.

 

When slowing down e.g. in a crawling line of traffic, if I am just on the throttle a tiny bit then back off to slow up even more it seems to just cut off. Almost like there is nothing between 700 and 1300 rpm. Is this something that can be fixed, or just one of those things?

 

Hope that makes sense, hard to explain, thanks in advance.

[h100vw 0]

There is a closed throttle switch on the TB. It obviously tells the ECU there is no throttle applied.

 

This would have the ECU cut the fuel by not firing the injectors during the overrun. This is an economy measure. As the engine speed comes down to around 1500 revs or so then the fuel is re-introduced to stop the car stalling.

 

If this cuts in too late(not adjustable) then it may feel that the engine is going to stall. Was a big issue with Pug 205 GTIs in the 80s, always stalling in traffic.

 

The cure was to turn the tickover up a touch and hope that it stopped doing it.

 

The other time it would come into play is when opening the throttle. As the switch opens the ECU would expect to see the engine speed up. If the switch was sticking closed briefly then the ECU wouldn't advance the sparks and up the fuelling. This would feel like bogging down.

 

I would have a look for the switch, not a VR expert having never had one but it must be there somewhere. Check its operation. You should be able to hear it click open and closed.

 

Gavin

[Kevin Bacon 5]

There isn't a switch on the VR, it's done by throttle angle. When the ECU sees a throttle angle of less than 14 degrees, it reduces the injector open time for overun & idle.

 

The VR can be a bit dead from idle to 1300 rpm, largely due to the ECU being confused as to whether the engine is idling or trying to accelerate. The angle between overrun/idle and acceleration is quiet narrow and when crawling in traffic you tend to flit between the two.....Running through the basic settings can help (in the knowledge base) with this.

 

It's a VR quirk and one I've learned to 'drive around'.... I'll get to the bottom of it one day, LOL!

[PhatVR6 0]

try cleaning out your ISV, air inlet boot and throttle body.

[h100vw 0]

Have you tried adjusting the pot to minimise the dead spot Kev?

 

Similar thing on motor bikes with carbs. Whenever you take one for a dealer service the grease monkeys introduce a mile of slack in the throttle cable so you've no idea when the throttle is going to open. Nasty to ride one thru traffic, a 4 stoke bike nearly stops dead at walking pace when you shut the throttle.

 

I always adjusted it out before setting off to prevent embarassment. Although that didn't stop me dropping the GSXR when the front tyre slipped while doing a burnout for the lads outside the block.

 

'Get it off me and stop laughing before I charge you!'

 

One of the benefits of RHIP, rank has it's priviliges :lol:

Gavin

[Yandards 0]

Yeah and bet they all just rushed over to help Gav....

 

...when they got up :wink:

[h100vw 0]

Only the ones that didn't know me, were actually able to move at all. Gits.

 

Luckily it was about 10 to 1 and most people had already set off back up the hill to work. Only about 2/3s of the singlies on camp were actually there to see me on my ar5e. :oops:

 

Got my own back on friday though, made everyone in my bay stay til 5 :mrgreen:

 

Something about 'power corrupts and absolute power, corrupts absolutely'. I think it was Gene Hackman said that.

[2cc 0]

oh how I miss all that

[RW1 0]

When slowing down e.g. in a crawling line of traffic, if I am just on the throttle a tiny bit then back off to slow up even more it seems to just cut off. Almost like there is nothing between 700 and 1300 rpm. Is this something that can be fixed?

 

 

http://the-corrado.net/.archive/forum/viewtopic. ... 9&start=60

 

“The TPS is harmonised in Basic Settings. Without this sequence the ECU guesses where the throttle is and so at small throttle settings and certain low rpm (Less than 1500 rpm).

 

That guessing results symptoms such as stalling on the overrun, roughish engine behaviour (like a slight misfire), the engine slowing slightly without movement of the throttle at small throttle openings, hiccup on pick-up from idle, dullness in the throttle response from shut until opened up a fair way resulting in the car leaping forward as things wake-up, ie. the ECU doesn't see throttle movement, then suddenly does.

 

Not every Corrado behaves the same as tolerance of components masks some of the symptoms. The errors in higher revs are less pronounced due to the driving not being, how should I say "delicate". “

 

 

The procedure is the second half of the Knowledge Base “ECU reset procedure”. The first part, ECU battery disconnect & drive does not need to be done every time. Basic Setting should be done at every 20,000 miles service. B.S. can be done at any time providing the condition of the engine is fully warmed up and there are no stored engine faults.

 

 

Basic Settings facility will only work when VAG-COM is fully registered.

 

 

“It's a VR quirk and one I've learned to 'drive around'.... I'll get to the bottom of it one day, LOL! “

 

I would tend to say it’s not a quirk. I see so many times the “reset” procedure being broadcast here in the recent past as “disconnect the battery and then drive”, no mention of doing Basic Settings follows in the same text. Do half the job, get half a Corrado VR6 engine. That’s why they end up driving that way. The WHOLE procedure in Knowledge Base must be followed. The second bit ain’t exciting, nothing moves, nothing clicks or clunks but at the end of it, the engine ECU knows where the throttle (ie TPS) is at, at all positions.

 

Of course if the throttle damper pot or other mechanical settings have been fiddled with around the throttle to try and “fix” the problems such as stalling, these will have to be returned to the correct positions.

[Kevin Bacon 5]

The knowledge base isn't very clear and some of the steps are repeated, does that mean we have to do it twice, or is it a typo?

 

"check CO", well, I ain't got a gas analyser so how I do that part?

 

"Rev and hold at 3000rpm", what, exactly or 'around' 3000 rpm....

 

This is why I requested a step-by-step procedure for VAG-COM users, not a quick 'wash through' such as exhibited in the KB. Then perhaps we can all have the other halves of our Corrados back? Would be much appreciated if you could do a laymens guide. I've searched Ross tech and there's nowt on there, so it seems you are the only person that knows how to do it properly.

[RW1 0]

-.

[RW1 0]

Hi Kev,

 

3,000 rpm. It's an arbitrary value. VW actually state "raise the engine speed". The procedure states 2,500 rpm. This comes about because people translate things differently in practice so I’ve compensated to ensure they wait, do, etc., sufficiently to trigger the conditions required. Not a precise engineering need on this one as long as the revs are raised held and released. You must have an engineering job! Only engineers are precise. :wink:

 

Likewise when disconnecting the ECU. The ECU looses it’s settings with 2 or 3 seconds but the 2 minutes is specified in case there is any “stored” charge is drained that may still power the ECU.

 

Repeated steps. Not sure which???

 

If the ECU reset & drive, they don’t have to all be done. The more samples in the first 10 minutes, the merrier. Basically as long as the car is driven in the first 10 minutes and not left just to idle, the lambda probe should get to somewhere near it’s correct settings before the “quick” learning mode shuts off.

 

If in Basic Settings, there are two pieces of text suppose to be in two columns. The left column is VAG 1551 dealer’s box keystrokes etc., the right hand side is the VAG-COM equivalent. When I looked at the knowledge base a while back, all the layout format I seem to think had been carried across, but not so today. Joe M in copying it has lost the layout of the original document. This is how it should look. I can’t alter the file up in Knowledge Base but having seen it today, it does need correcting for those peeps less familiar with VAG diagnostic procedures.

 

Ross-Tech, yep it's there, tucked away in the Uwe’s Yahoo support group files section, not on the VAG-COM site itself, follow the link in the support/forum section to http://autos.groups.yahoo.com/group/VAG-COM/.

 

Quick wash through - there ain’t any more I could add, hopefully if the KB layout miss-mash of Basic Settings section is rectified as per the file (to preserve the layout) it will help to make it clearer, if not….. what’s puzzling you and I will expand. Perhaps being a VAG-COM v0.5 veteran, I’m too familiar with the product. What I have done is collate the diagnostics into a procedure derived from various points in the manuals, about 16 volumes for the european Corrado. And If I remember rightly, a VW bulletin was also involved in the Basic Settings procedure.

 

VW diagnostics hinges around having the Corrado workshop manuals to hand and as Uwe Ross states, VAG-COM another wrench in your toolbox. The manuals aren’t written specifically to have sections on diagnostics, more you pick up the required tool and if some cases it may be VAG-COM. The B.S. information is in the USA Bentley Manual for instance but the text is integrated into doing a repair/adjustment. It’s why the measuring blocks have so many repeats of same fields in various groups. A group of four fields corresponds to a repair task in the manual. This so the mechanic is not flitting around the diagnostics trying to find a parameter to read while carrying out a task.

 

CO level, well, if you have something like the Gunsons CO tester which I don’t or any other either you have to assume that all is OK. MoT test emission data if requested when picking up the C will give some confidence to that.

 

Perhaps sometime at a show we both happen to be at, we can have a chat. Did find your C at GTinters but no bodies!

 

Chris

[Kevin Bacon 5]

Brilliant, thanks Chris!!

 

I'll have to collate something together and do a sticky as there are number of folk with poorly VRs at the moment.

 

Yeah likewise, I wandered over to the CCGB area and again, no bodies!

I found it amazing that with so many Corrado owners in one place at the same time, we still all missed eachother!!

[RW1 0]

Wasn't on the CCGB stand. Came in the hack Scirocco for the weekend.

 

Give things a try on yours and see if it comes clean.

 

Could do with sorting the KB some how. Can you do anything as a Mod?

[Kevin Bacon 5]

Only Andi can change things in there.

 

Yeah I'll run through the basic settings after the charger is fitted Chris because it'll get a new chip and 6 new injectors, and the induction tracts will be completely different, so may aswell wait till then and set it based on the new configuration.

 

Mine exhibits precisely what you say about it not knowing where the throttle is symptoms below 1500rpm, so looking forward to ironing that out, although I suspect with circa 290hp on tap, that'll probably be the last thing on my mind :lol: