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[MarkG]

Under full power my car judders and surges violently as the engine feels like it cuts in and out and continues to do so for as long as I keep my foot planted. It feels like the ignition dies and returns for a millisecond. Ease off the throttle and the engine feels smooth again. It did not happen on the way to work this morning but did on the way home.  It is worse when cold when even light throttle can cause juddering and even a stall at idle. There is no EML,  or any other indication that anything is wrong.

So far I have:
replaced DIS pack (with a new Bosch unit)
replaced plug leads
replaced plugs (from Vx dealer)
cleaned out all breathers
cleaned out throttle body
checked and fixed vacuum leaks
cleaned out ICV

I'm thinking now maybe a bad earth strap? If so, where is it strapped to the car body?

Can anyone suggest anything else to check?

Thanks fellas

Mark

[Gaffers]

Last time I had violent juddering it was due to 2 out of 3 diff bolts missing.  Have a look underneath the offside of the diff.  If you dont see 3 huge bolts there you may be missing one...

Just a thought before you go on a search for the holy grail    

[arthill]

Always better getting ecu read before spending, could be MAF,or EGR or possibly Cam sensor, but better getting any fault codes first.

[TheBoy]

Worth doing a paperclip test to read codes for free

[Mr Skrunts]

I had a bit of a problem like this a while back, the car had been running fine, was following a car and was getting a bit bored as I thought the driver in front was falling asleep.  The car hadn’t had a good run for ages so I decided to stretch it’s legs a little, waited for a nice long open stretch and booted it, all went as normal, dropped a gear and then all of a sudden it started to surge but had lost all it’s power, it was like riding a race horse but there wasn’t any power, I backed off a dropped behind the slower car and all was fine,  but every time I hit the power the problem returned.

I drove through a village trying to work out what the problem was, it was ticking over ok, it drove ok at low revs but as soon as I wanted more power the problem returned.  There were no warning lights no other problems apart from my brain ticking wondering whether it would be a £100 repair job or a £200 repair etc.

Anyways, I was so pissed off I got past caring, I put my foot flat to the floor from 20 mph it was like watching paint dry.

It slowly went from 20 mph to about 70 mph (felt like an eternity) but I kept my foot down, dunno what I was expecting to happen thinking it might have been a fuel issue, then the was an almighty bang and as I looked it the rearview there was a big cloud some sort of dust and smoke, BUT at the same time the front of the car rose, the back end squatted down and the V6 suddenly started to sing a very happy tune similar to an F1 car.

I got to my mates to find out that the rear exhaust box had filled up with the horse hair wadding stuff the silencer was lined with, but on further examination the rear box had split/exploded but the surging problem and loss of power problem was cured.

Could the exhaust be part of your problem?

[MarkG]

Just done the paperclip test and inspite of no EML showing it came up with 73 and 74 which are MAF high and low voltage. Where exactly is this and what do I need to check please?

[TheBoy]

Just done the paperclip test and inspite of no EML showing it came up with 73 and 74 which are MAF high and low voltage. Where exactly is this and what do I need to check please?

Before condeming the MAF, check for air leaks.

[Marks DTM Calib]

I assume the fuel filter is ok......

[SP_3.2]

 had the same prob as you and it was a very small hole in one of the lines goining  in to the fuel pump under the boot. Cut off the bad part of the rubber hose and all was good.

do you smell any fuel

[MarkG]

Fuel filter was supposedly changed 13,000 miles ago so it should be OK. I will change it  this week-end just to sure. No there is no fuel smell but I will check the lines too  

[MarkG]

WOW. My car is back to its old self again. I decided put my old MAF back on earlier in the week and the car has gone like a bomb ever since. No dodgy tickover, no hesitation and smooth acceleration under full throttle.

When I started chasing down the car's fault about 6 months ago, one of the first things I did was to change the MAF - not for a Vx one but for a cheaper one off eBay. That was a mistake. Good job I kept the old one.

The dodgy eBay one has an arrow showing direction of air flow on the main case but i just spotted that the actual sensor has an arrow going the other way. The old Vx one has both arrows going the same way (downwards). But the sensor on the eBay one cannot simply be turned through 180 degrees because the screws are off-set.

Hope someone finds this useful.

Cheers guys

Mark