VR6 throttle oddity

[Kevin Bacon 5]

Just recently my engine has been very jerky at part throttle...kind of coming on/off abruptly just off idle, which makes urban driving a real chore.

 

I've put this down to the throttle pedal needing to be pressed at least 2cms before the engine starts to rev. I've checked the throttle cable and it's fine and VAG-COM is showing the correct idle and WOT angles. I'm stumped and so is Vince as he's not seen that before apparently.

 

I think it's a mechanical issue related to the throttle but I'm not sure what yet.

 

Anyone got this on their VR?

[Guest]

I would look beyond the action of the throttle as there are many things that can cause this. If you have a leaking high tension lead or the coil / coil pack is on its way out you will also see this kind of hesitation. Take a plant mister and lightly mist the leads at night and see if you can see any sparks grounding out. I would also pull the plugs and check their condition while you are at it. You may also want to use a timing light with an inductive pick-up and make sure you are gtting even spark and no misses. Ignition is very important so I would check and make sure everything is up and working properly.

 

The throttle switch seems to be working properly as you have checked the throttle angle. When you had the VAG-COM hooked up did you compare the readings of the ECU temp sensor with the engine coolant gauge? If your blue ECU temp sensor is giving false readings it can cause the car to run lean / rich which will also give rough part throttle response. Same goes for the O2 sensor, these can really change the way the car runs so I would check them out.

 

Vacuum leaks will also change the way the car responds so I would go through the intake system and make sure there are no vacuum leaks. Make sure the EGV valve and charcol canister purge valves are closing and not allowing extra air to enter the intake system. Check all of the small vacuum lines as well, if the small vacuum line going to the FPR is not working it will raise the system pressure from 50 psi to 60 psi by itself. I would also take a look at the system fuel pressure, a weak fuel pump can also cause this kind of problem but typically you can feel it more at high revs than low. It may be worth pulling the injectors and testing for proper fuel flow and make sure none of the injectors are leaking. System fuel pressure is easy to test using a pressure gauge Fuel Pressure Testing. Leaking injector seals can also cause a vacuum leak which will change part throttle.

 

I would also make sure the car has good grounds, you can use a pair of jumper cables to test this out. Make sure the alternator is putting out a good charge and the battery clamps & cables are in good shape. Last and most famous is the igntion switch, I would stick a known good one in and see if that makes any difference. That little crappy switch takes a lot of amperage and they do burn out so I would take a hard, cold look at that as well. I am going to take the time one day to calculate how much amperage it actually takes so I can use relays to reduce the load on it and make it last for a long time.

 

How does the car run otherwise? When you are driving do you notice any problems or is this just on & off throttle? What's the weather like over there lately? Lots of rain and moisture will really get a leaking coil to act up or the leads for that matter. Does your car have a coil or a coil pack? Wait, it's a 1994 so it has a coil pack. Take the coil pack off and take it apart and see if you can find any signs of leaking. The coil packs usually leak where the arrows are in the pic below. The cam position sensors on these car also go so I would think about that as well. No cam position sensor then no sequential injection or proper knock sensing.

 

http://members.shaw.ca/vr6_corrado-2/Coilpack06.jpg

 

I would think about some of the stuff above and see if that brings any ideas up or solutions.

 

Cheers, Dennis

[Henny 0]

Kev? Check the rubber grommet in the pedal which holds the accelerator cable into the pedals lever.... 2cm play sounds like it may have gone soggy... ;)

[Dick Dastardly 0]

I've been having the same problem slow response from the car when accelerating and also slow response when taking the foot off the throttle(engine revs stay high for a few seconds after releasing the pedal). First stop was the ignition leads they looked like the originals and since the car has covered 160,000 plus miles i thought the were looking pretty bad way, it was also worse when the weather was damp (raining) it felt like is was mis firing. Just got the Hazet tool to remove the HT leads yesterday, so I don' have conclusive proof but I have to say the throttle response so far is very smooth there doesn't appear to be the "Lag" that there was before the new leads were put on. I also sprayed the exterior of the throttle body and the cable with plenty of WD40 just in case it was sticking. (changed the spark plugs while I was at it)

 

Worth a try checking the HT leads

[Tekara 0]

Mine has exhibited this trait at times, normally when cold its noticeable up to roughly 2200rpm. I had my coil pack, leads and plugs replaced at the end of last year. To be honest ive not really looked into it too closely, ive had mine on VAG-com too, no faults.

[Kevin Bacon 5]

Dennis - Good post dude!

 

Going through your checklist, I have unfortunately done all you've said.

 

The following are new or installed within the last 12 months:-

 

Throttle cable - plugs (platinum) - leads - cam sensor and trigger wheel - crank sensor - fuel pump, fuel pump, ECU and Load induction relays - Ignition switch (VW) - Blue temp sender - ISV - throttle potentiometer - throttle dashpot - Intake temp sender - ECU - throttle body - O2 sensor - PCV breather valve.

 

Testing:-

 

Alternator - fine, 14V.

Grounds uprated to 0 guage amplifier wire

Additional 4 guage earth from battery negative to head

Coilpack - fine, no arcing at night

Carbon canister frequency valve - fine.

EGR valve - Only you guys got that.

Intake leaks - None that I can detect with squirts of carb cleaner.

 

The head was also rebuilt last year and all the chains/tensioners replaced.

 

When driving it's quite good, loads of grunt and smooth. It's just the part throttle behaviour that's erratic. So long as I stay away from 1500 rpm, it's fine.

 

I think I'll book it into my trusted garage as my Schrick manifold has developed a fault (the flap is rattling at idle) which they will need to look at anyway. I've been trying to solve this part throttle business for 2 years to no avail and it's always done it, standard and modified. I've driven many VR6s and they all seem to do it, but mine's worse than the others.

 

What I have noticed is it's quite smooth and responsive when cold and during warm up, and then as soon as the lambda kicks in (after 2 mins) the idle and part throttle go to sh1t. The revs drop like a brick when hot, but fall gracefully when cold. Fuelling?

 

I hope to get there in the end!

 

Henny - Grommet is fine chap as I replaced the cable tonight.

 

Dick Dastardly - I'm tempted to stick some OE leads on. Got some aftermarket ones at the moment which could be breaking down or something.

 

Bl00dy Corrados :evil:

[Guest]

Dump the platinums and see how things change, the VR6 really likes the NGK BK5REKU plugs. I'm not sure if you know or not but most platinums are actually platinum coated except for plugs such as the G60's Bosch W6DP0 which have a solid platinum core (which is why they are worth their weight in gold). Anything that is only coated is pretty much worthless, if you have a set of old plugs pop them in and see if it helps. Many Audi's will barely run with platinums and my findings in VW has been to avoid them.

 

You can't really see any leaks in the coil pack unless you strip it right down so you might want to do that. Ignition switches are always a good starting point as they are prone to failure and they can drop the true ignition power levels enough so at low rpms you have problems until the alternator can make enough power. The alternator output should also be tested under load to make sure it can supply enough power & check the brush length on the regulator while you are at it.

 

I have heard that some of these problems are due to the factory software in the ECU and a chip will help correct that and bad mileage. I don't think it is a wise idea to upgrade the chip if the car isn't running correctly but if you know someone with a coil pack Corrado and a chip it might be interesting to swap out the ECU.

 

I know what you are talking about with how the car runs hot to cold though, it must be a VR6 thing. My 1994 Canadian spec (2.8 litre, coil pack, air pump, and EGR) exhibits the same conditions to some degree but far less noticable. When I am on light throttle the car also seems to almost be missing on a cylinder every two rotations. It is very slight but I can feel it but I just thought it was me. I have replaced most of what you have plus I have checked the system fuel pressure and have come up with nothing. I was thinking of taking it to a shop and having it put on a exhaust gas analyzer and seeing exactly what the car is doing. This is where one of the suggestions with the chip came from, I will use the analyzer first.

 

Also, your intake will reduce the bottom end power so you may want to swap the upper manifold with the stock one (or send it me, either will work) and see how that changes things. See if you can find a buddy with a chipped ECU and try changing that and use the factory plugs.

 

These are always the hardest to solve when you have changed so much and there is not much left from stock. I have heard other people really get an improvement from cleaning the MAF, I swapped mine with buddies B3 VR6 Passat and it made no difference.

 

Best of luck, Dennis

[chargedupstorm 0]

kevhaywire, Does it feel like the car is about to stall, then the revs climb again?

If so I had a similar problem many years ago before I modded my engine, and the culprit was the MAF of all things. I only noticed it when I was logging with VAG com, for some reason at idle the air flow was too turbulent over a faulty or dirty sensor.

 

It's worthwhile either cleaning the MAF film with carb cleaner, or alternatively borrowing someone elses to rule this out as a problem.

Good luck!

When you say your schrick flap is rattling at idle, do you mean the valve or the flap itself? I had a noisy flap and it turned out to be a washer vibrating on the allen bolt that held it to the manifold, the bolt was actually all the way into the thread but was .02mm too long so it never nipped up to squeeze the washer tight and rattle free!

[dr_mat 0]

* Contribution removed for value reasons.

[Kevin Bacon 5]

Dennis - Thanks again. The alternator is also new, forgot to say. I don't think there's much under the hood that isn't to be honest.

 

With the plugs, the engine doesn't run any differently with the NGK BK5REKUPs than it did with the BK5REKUs, in fact, that's all VW will give us in the UK for the VR6 now. The 'EKU has recently been superceded with the EKUP on the parts system. I'm not a believer of fancy plugs either but that's all I can get now.

 

When I took the EKUs out the other night, all 6 were absolutely perfectly uniform in colour (brown coating on the centres and grey deposits on the grounds), no oil contamination either, so the engine is healthy and exhibiting a good burn overall. I don't get it.

 

Manifold, yeah the Schrick delivers less torque at 1500rpm than the standard manny but few people actually notice it on the road, we're only talking 10ft/lb at the most.....and no you can't have it :wink:

 

MAFs - Hmmm...I hate the darn things. I've had 3 in the past 2 years, one of which arrived dead! Why can't Bosch produce a MAF that lasts more than 5 minutes?

 

Guy - Yep, pulling up to junctions sometimes sees the revs drop right down and then they recover and blip up again sharply. I've wound the dashpot up as far as it can without moving the throttle off it's stop, which has helped a bit, but I think it's looking like another MAF as VAG-COM is perfectly happy and we all the know the MAF is not monitored by the ECU...all it cares about is the electrical connection!

I'll get Vince to stick his known working MAF on when I go up there.

 

The Schrick - Sorry yeah I meant the flap itself. I heard a curious noise last night and did the stethoscope thing and sure enough, the flap is rattling about inside the manifold.... I can't remember the reason or the fix but I know a man who does, LOL!

 

Dr_Mat - Thanks mate, really useful contribution :roll:

[Cnut 0]

Kev did you ever get to the bottom of this? Because my car has the exact same symptons...

[Taggart 0]

Wow, I'm impressed, someone used the search :)

[Supercharged 2]

xbones, How much did Tom pay you to say that? :lol:

 

Damn good thread tho!

[Taggart 0]

I just hate it, cuz if I post a repetative thread (or go really OT) Tom'll stop putting out :(

[VR6 0]

Jokers :lol:

 

Hmm, think it's time for bed.

[Yandards 0]

Jokers :lol:

 

Hmm, think it's time for bed.

 

On your own? :wink:

[Cnut 0]

Any useful contributions to the thread would be appreciated :roll:

[Guest]

Wow, I'm impressed, someone used the search :)

 

rofl :lol:

 

all my sarcasm has paid off at last! :)

[Kevin Bacon 5]

Kev did you ever get to the bottom of this? Because my car has the exact same symptons...

 

The problem went away when I ventured into Forced induction.....so that's an expensive way to cure throttle snatchiness :lol:

 

From memory, I'm sure it was the MAF causing it. It seems to cause a lot of issues in the low rpms and idling when it's duff.

[Cnut 0]

Kev did you ever get to the bottom of this? Because my car has the exact same symptons...

 

The problem went away when I ventured into Forced induction.....so that's an expensive way to cure throttle snatchiness :lol:

 

From memory, I'm sure it was the MAF causing it. It seems to cause a lot of issues in the low rpms and idling when it's duff.

 

Thanks, that looks like another one to add to list :(

 

Would you expect the symptons to dissappear with it unplugged or would it be the same?

[dr_mat 0]

Symptoms could go away, they could not, it depends on exactly what's wrong with your MAF ...

[Cnut 0]

I unplugged it last night, the engine didn't stall or anything but the throttle response was crap and the revs dropped quickly but hesitation was still there.

 

I take it this means that my MAF is still working?

[dr_mat 0]

It's working mostly, yep.

Mine does the same, and I'm pretty confident my MAF is ok.

[Cnut 0]

I cleaned it out last night anyway with some contact cleaner, I dont think it made any difference.

 

The coilpack, ht leads, sparkplugs have all been changed recently so that rules them out. It makes me wonder whether it might be a fuel starvation problem because the fuel pump is very noisy, I changed the fuel filter but that made no difference to the noise so im gonna order a new pump today. How many fuel pumps are there on a VR?

 

I have ordered a set of injectors and rails off JIMMI so they will be getting replaced for some newer ones.

 

Would it be worth changing the TPS while im there?

[adevr6 0]

i would check tps and wiring to it.replaced mine and it has cured throttle respose on a mk3 sc vr.