VR6 flatspot - MAF problem?

[Robbo149 0]

Hi all,

 

I've got a bit of a flatspot when driving my VR & it's starting to really annoy me. It only seems to happen when I take my foot off the gas and then press the accelerator again, I'm getting a really bad hesitation where the engine seems to stutter & lose power for a couple of seconds & then it will accelerate out of it. Otherwise the car drives great. Could this be down to plugs/leads/coil pack, or is it more likely a fuelling problem? Any advice greatly appreciated, it's starting to spoil the fun!

 

cheers.

[16vgt 0]

sounds like its a fuelling problem. or maybe even an air problem.

have you checked the airfilter etc??

[dr_mat 0]

Have you done an ECU reset recently?

Often helps on stuff like this? Maybe it needs to re-adapt to the characteristics of your engine.

[Kevin Bacon 5]

Check the throttle cable isn't slack. You can adjust it with the clip on the cable. Remove the upper HT lead tidy and all will become clear.

 

Kev

[Robch 0]

How do you do an ECU resest?

[Guest]

Unplug the battery

[jedi-knight83 0]

Unplug the battery

 

how long does the battery need to be undone for?

[Kevin Bacon 5]

About 15 minutes

 

Kev

[Robbo149 0]

Does this erase any fault codes which may be stored?

[Henny 0]

yup. 8)

[DEL VR6 0]

i got the same problem. it seems to happen more when the engine is still cold, and has been happening more than it used to since i had the 57i Induction Kit fitted. Can be really annoying. (i havent had the ECU reset by the way)

[Robbo149 0]

The stuttering on mine seems to be the other way round - it's not too bad when the engine's cold, worse when it's warmed up! It feels like there is either too much or too little fuel getting through after the overrun (when I take my foot off the gas), so when I press the accellerator again it splutters for a few seconds & won't pull! Can get quite jerky if I'm heavy with the right foot!

[Kevin Bacon 5]

I find the VR responds better with light throttle inputs at slow speeds. If you're getting stuttering and flatspots when applying the gas after overrun, try checking the O2 sensor and MAF sensor. O2 can be checked with a multimeter. It should fluctuate between 0.1-0.9 at idle when warm and sit at 0.7 at 3500rpm constant, 0.8 at wide open throttle. The MAF there is no real check for, the ECU only reports "intermittant short to ground" or "No signal". Either of those cases means it's dead, but it may not show up at all but still be operating out of range, in which case you simply unplug it and see if the car feels any different to drive. If it doesn't, it's dead (Throttle position sensor is the substitute).

 

02 Sensors are £52 from VAG with Corrado club discount (£72 without) and MAF sensors are £150 exchange from Bosch.

 

Kev

[jedigtr 0]

I had a similar problem with my VR6, the local garage couldn't fault it when it was in for a service and it went on for quite a while. Eventually it did it whilst in their hands and they traced it to a dodgy hall sender (or whatever its called) replaced it and it was as good as new :)

[Robbo149 0]

Okay, I warmed the engine up, unplugged the MAF plug and the car drove exactly the same! (plugged it back in & the engine cut out). So the MAF sensor is dead, right? :cry: Does this mean the only solution is a new one?... anybody got a spare one??? Do I also assume that because the car is still driveable that the throttle pot is OK?

 

Cheers.

[Mike Edwards 0]

Okay, assuming that all the other sensors are working fine:

 

Start the car and let it idle until warm.

 

Unplug the MAS.

 

The revs should drop. If there is no change, the ECU has adapted to having no signal from the MAS. Disconnect the battery for a few minutes, reconnect and repeat. Try driving it - it should feel 'orrible if the MAS is gone.

 

Could be the MAS, could be the wiring.

[DEL VR6 0]

I've been told by the local VW "specialist" garage that i got a dodgy "hall" sensor. Thing is i keep ringing for an estimate, and they are taking forever to call me back with it. Will keep you posted on this one.

[Mike Edwards 0]

The part costs ~£30, and can be changed with nothing more complicated than an allen key.

[Robbo149 0]

Thanks for the advice Mike. Had the battery disconnected last night (ECU reset) & tried again this morning... There's definitely no difference with the MAS unplugged. Not sure I would describe it as "orrible", it's just bit a spluttery when accelerating after taking my foot off the gas. This being the only VR6 I've driven though, I don't have anything to compare it with. Because it still drives ok generally, does this mean that the ECU is defaulting to the throttle pot & that's doing its job ok? Are there any other tests I can do to narrow the problem down? or do I need to get the fault codes pulled?

 

Cheers again.

[Kevin Bacon 5]

Yeah hook it up to VAG-COM. If you're lucky you may get an "Implausible signal" or "Intermittant short to ground" or just a plain old "No signal". Historically, the MAF rarely throws a code but they do operate out of range when fooked, which the ECU seems to ignore, from a coding point of view. I'm sorry to say there is no definitive way to check it, I had one of mine checked on an Oscilliscope by a local Bisch Basch Bosch agent and it passed the waveform tests, but the car still drove like a bag of squished turd.

 

They say this always happens with MAFs, Beetles, Golfs, Subarus, BMWs you name it. They just go without warning with no clue as to what's up with it.

 

Only cure is to replace it. They did me a recon one for £150, which is basically new innards inside a used plastic housing, but when you look at the one they send you, it is infact new anyway, so go for a recon one.

 

You are correct in saying the ECU uses the TPS as a substitute, but TPSs aren't very accurate and it's a crude method of fuelling, hence the jerkiness and flatspots you are experiencing.

 

You might also want to have your ECU scanned for Cam and Engine positon sensor errors.

 

Kev

[corradovr6sc 0]

My car had the same symptoms (flatspot and stutter) when the cam sensor was on the way out but drove ok when the maf failed but the ran very rich.

[Jimbo 0]

yep sounds like a dodgy hall sender unit to me! :(

 

Thats the little sensor that send vital info back to the ECU. Not expensive though and not a difficult job and is a fairly common fault on VW's esp VR Corrado's :D

[Robbo149 0]

Cam sensor & hall sender... are these the same thing?

 

I'm having a Bosch diag test done on Friday, see what that throws up! Basically I'm trying to identify any cheaper possibilities to replace before going for the biggie! (£150 - £200 for a new MAF sensor). I'll let you know how I get on.

 

Cheers for all the replies guys, these problems are never black & white are they!

 

p.s. I've downloaded a list of numeric fault codes for the Motronic 2.9 system if anyone want's to know what any codes mean.

[dr_mat 0]

Is there any way of getting a LED hooked up to the ECU that will report "an error has occurred" sorta thing?

In the absence of a local VAG-COM (and regular checks) it would be so nice if the engine would just TELL YOU when something went wrong, so you could go get it checked out. I mean, it has the ability, why on earth does it keep it to itself all the time?

It can do it for the ABS, so why not the rest of the sensors?

Or is it because these sensors bug out all the time, on and off, from new, and VW found that people would be bringing the cars back every other week?!

[Kevin Bacon 5]

Cam position sensor is the correct terminology as it sits opposite the cam picking a signal from a magnet. Hall senders traditionally live inside distributors, but their job is the same. Just being nit picky :lol:

 

Dr_mat, indeed the ECU can flash an engine issue light, just ask our American friends. They got such a light on their cars.

 

You can buy a nifty gadget called SECS which monitors all the ECU functions on a backlit LCD panel. Currently it's for Subarus but the manufacturers of it have made them for VWs though.

 

Kev