Car Jerks with light acceleration

[shamoo]

ever since i got my custon re-map the car jerks forward in 3rd (alot) 4th (a little) and 5th (in beteween 3rd and 4th of the jerkyness) this only happens when my foot is at a constant pressure on the accelerator for expample slowly accelerating in 3rd, i've also notcie it happens when the dump valve is making a noise, it starts and finishes together. i'll try and explain a bit better:
driving at 40 in 3rd and slowly accelerating when the dump valve woshes and at the same time the car jerks then they both stop, this happens nearly everytime, 1st and 2nd gear are fine and over 70mph its fine, its to the point now where i'm starting to hate driving it, i use it as a family car and wanted the power for when i'm in on my own not driving along and then the car start jerking almost like i'm tapping the accelerator. i actually think its not doing the car any good and then today whilst the car was jerking, the "diagnosis/excess of pollution" light came on, it drove fine but when i put my foot down the light stayed on, when it started jerking, the light flashes? does anyone know what the hell is happening to my car or is this just a crap re-map or is there more to it? i'm now in two minds to put the ecu to standard and then save up and get a revo/jabba map. Also i know i should drive it more, at the moment i driving it about 20miles a week, surely this wouldn't cause this problem? its been happening since i got the map.

 

[Romeoisgraham]

Could be your N75 valve, or your coils (common fault)

Put in a thread in the diagnostics section asking if anyone in your area has vag com.

 

[shamoo]

i've just changed the coils and its driving "fine" well the usual way it does, anyway lol

 

[shamoo]

what is a N75 valve and what does it do?

 

[Leigh15]

It controls the boost I believe

 

[shamoo]

is there a way i can check it or would it need a mechanic? would it be the d/v? it just seems to happen when the d/v releases pressure?

 

[xd-data-ii]

ever since i got my custon re-map the car jerks forward in 3rd (alot) 4th (a little) and 5th (in beteween 3rd and 4th of the jerkyness) this only happens when my foot is at a constant pressure on the accelerator for expample slowly accelerating in 3rd, i've also notcie it happens when the dump valve is making a noise, it starts and finishes together. i'll try and explain a bit better:
driving at 40 in 3rd and slowly accelerating when the dump valve woshes and at the same time the car jerks then they both stop, this happens nearly everytime, 1st and 2nd gear are fine and over 70mph its fine, its to the point now where i'm starting to hate driving it, i use it as a family car and wanted the power for when i'm in on my own not driving along and then the car start jerking almost like i'm tapping the accelerator. i actually think its not doing the car any good and then today whilst the car was jerking, the "diagnosis/excess of pollution" light came on, it drove fine but when i put my foot down the light stayed on, when it started jerking, the light flashes? does anyone know what the hell is happening to my car or is this just a crap re-map or is there more to it? i'm now in two minds to put the ecu to standard and then save up and get a revo/jabba map. Also i know i should drive it more, at the moment i driving it about 20miles a week, surely this wouldn't cause this problem? its been happening since i got the map.

I had the same problem and annoyed me. Went through all sorts of things to see what the problem was. Wasted €100 on a new MAF and nearly got new coolant temp sensors and N75 valve.
In the end, for another reason, i got the map modified and it cured all problems. the mapping was the problem
And i suspect it is definitely the problem with yours. Get them to check it again and try a revised map

Also new mappings seem to change the throttle duty cycle and when you come off the accelerator when under boost the car feels like it jerks suddenly a little and is not as smooth as standard. Apparently some like it this way. I got that effect lessened when i got my map re-modified

 

[ChrisJ]

I had the same problem and annoyed me. Went through all sorts of things to see what the problem was. Wasted €100 on a new MAF and nearly got new coolant temp sensors and N75 valve.
In the end, for another reason, i got the map modified and it cured all problems. the mapping was the problem
And i suspect it is definitely the problem with yours. Get them to check it again and try a revised map

I would agree, i expect the mapping's just a little to aggresive. Mine does this to a degree, but i just learned to live/drive with it i guess.

 

[Stu_pot]

A lot of confusion occurs due to different peoples description of the problems and symptoms of similar sounding faults and issues.

Mapping isn't always the problem however it is more likely to show up existing or new problems, for want of a better word, elevated levels of boost and timing can make the ECU more 'sensitive' to out of normal range engine and sensor parameters. A modified remap could certainly cure some peoples problems but it is only working around or 'smoothing' out any existing issues.

My problem since I've got the car has been fluctuating boost on light to part throttle below 4000rpm, this exhibits itself as jerky acceleration. It seemed fine on WOT.

If I kept the throttle light and constant and tried to be as linear as possible with light acceleration, you could feel a 'surging' as the boost ramped up and down.

I cured it today with a replacement MAF, I had a spare one from my S3 and luckily it was an identical part number. However, I knew there was a problem with it after logging with VAG-COM. Also after checking for no sensor errors, it's the first place you should start - It's the first sensor in the power cycle after all !

My other point is this, notice I have used at least 3 adjectives to describe the conditions I experienced on this particular car (I have had 5 1.8T engined cars to date) :-

'Jerkiness'
'Fluctuation'
'Surging'

There is a plethora of threads regarding this and similar issues but they all contain the above descriptions and there is an even bigger plethora of suggested fixes and ideas, 80% of which are based on guess work from people with no real mechanical knowledge or background.

However, peoples experiences of what fixed their particular problem IS invaluable information but should NOT be taken as gospel.

My suggestions are these :-

DON'T waste your money swapping parts that seem to be the common problem, it might never cure your problem! However, you may strike it lucky.

DO invest in VAG-COM and invest some of your time learning how to use it, especially how to log engine parameters under certain conditions, this is the most INVALUABLE tool you will ever own for a VAG car.
With a moderate level of understanding and knowledge you will be better equipped to problem solve than most MVT's.

DO be methodical and LOGICAL in your fault finding, trust your first instincts. Using the forums suggested fixes and suggestions, compile a check list and re-order it with common sense and your own gut feeling of what YOUR problem is.

 

[xd-data-ii]

Give it a week. The problem may just well return.
Did with mine. Thought the maf change had sorted it and after a few days the problem returned.

But if the logs are not right then i suspect you did the correct thing by changing it.

 

[shamoo]

wow thanks for the replys. i will buy a VAG-com soon, but typical like anything its happened at the wrong time, next month would be fine but the last few months i've been paying back debt. i personally think its the map, since its only happened since its been on. i'm thinking if the vag-com doesn't pick anything up, i will cut my losses and put the ECU to standard then save up and get a revo map. now is revo nice and smooth? i want the map to accelerate as smooth as the car does standard but just faster.
also what vag-com kit would i require?

 

[xd-data-ii]

Every car is different and the map should be adapted to suit the car through feedback from yourself. Just get them to get the existing one right.

 

[shamoo]

i will try. there's going to be another post from me sort of linking the 2previous ones together as i got another fault this afternoon. so pls read it and advise.

 

[shamoo]

http://www.seatcupra.net/forums/showthread.php?t=160404

this is the thread to the new problem could it be linked?

 

[ChrisJ]

i personally think its the map, since its only happened since its been on.

But thats just it, the Map has amplified any underlying faults that wouldnt have caused an issue before. So its not definatly the Map, its the map which has bought it to light.

 

[Stu_pot]

But thats just it, the Map has amplified any underlying faults that wouldnt have caused an issue before. So its not definatly the Map, its the map which has bought it to light.

I'm convinced I already said that

 

[shamoo]

But thats just it, the Map has amplified any underlying faults that wouldnt have caused an issue before. So its not definatly the Map, its the map which has bought it to light.

fair point, after its been to the garage and had a propper going over and every thing fixed i'll take it to a specialist about the map IF its still happening and the garage has said the car is fault free.