2.0 HDi 407 - Lumpy/surging at low RPM

Blue407 · Post by **Blue407** » Thu May 03, 2007 8:07 am

My 407 is what I can only describe as lumpy at low RPM (1400-2200).

When driving at a steady 30mph in 3rd or 4th if you touch the throttle, even lightly, it will surge forwards. Trying to keep you foot in the same position on the throttle results in the car ever so slightly surging forwards and then easing off. There is no noticable change in tone from the engine.

It has a service only a week and a half ago and seems to have been doing this ever since. This was it's first service at 20,000 which I believe is primarily a check over and oil change.

There is no noticable lack of power and I have given it a good blast down the bypass to clear out any 'cobwebs'! I have even just changed the air filter and it made no difference. I put a can of Forte diesel injection cleaner in the tank at the weekend.

Suggestions? (Maybe try a new tank of diesel as it's nearly quarter full now?)

Post by **Welly** » Thu May 03, 2007 8:21 am

Even my old 2.0 HDi does this a bit.

Have you ever tried to 'hold' a certain revs in neutral and parked up? - It's impossible! I cannot hold the HDi at a certain revs and I don't know why. You can get it to hovver at around 2000 then it will just change higher or lower itself and you never moved your foot a milimeter.

If I'm in 3rd or 4th at low speeds, the *slightest* touch on the throttle makes it forge ahead with no 'real' input from you.

The only time my car is 'lumpy' is in 2nd gear at about 1200 revs you can feel each compression stoke of the engine but that soon goes over 1300 -1400 revs.

If you feel something has changed since your dealer service then go back?

Blue407 · Post by **Blue407** » Thu May 03, 2007 8:25 am

Welton wrote: If you feel something has changed since your dealer service then go back?

I was going to give them a ring today to see what they have to say. However if it is worth putting a fresh tank of diesel through first then I would do this.

I am just wondering if I am being over sensitive and if it has always done this!

trem1 · Post by **trem1** » Thu May 03, 2007 6:11 pm

try a tankful of bp ultimate first, mine seemed a bit lumpy and noisy so i tried ultimate which did seem to make a difference it seems quieter and more responsive than when i ran it on morrisons cheapest

try it yourself see what you think

jameslxdt · Post by **jameslxdt** » Thu May 03, 2007 7:09 pm

these are unfortunatley the characteristics of a HDi or any common rail diesel, only the vag pd engines dont suffer with it
though it may be a sign of a throttle potentiometer with a dead spot

Blue407 · Post by **Blue407** » Fri May 04, 2007 7:45 am

trem1 wrote:try a tankful of bp ultimate first, mine seemed a bit lumpy and noisy so i tried ultimate which did seem to make a difference it seems quieter and more responsive than when i ran it on morrisons cheapest
try it yourself see what you think

I've been waiting until the tank was low before trying BP Ultimate as I want to get the max BPH from the rolling road session.

Put £10 BP Ultimate in this morning to dilute the remaining few litres of std BP Diesel, should be able to fill up with a full tank of Ultimate by Tuesday.