intermittent tdi performance

[glynnd]

I have a poor peformance issue with my cupra tdi
I have cleaned out the egr replaced the maf put forte throught the fuel system made sure the vnt rod moves freely and is not sticking, but my car performs average for a period of time and then fab then goes back to average again.
When its poor i cannot outrun a 120bhp astra cdti sri.
Its not overboosting does not go into limp mode but had vag com connected while i took it for a blast never throws a fault code up but vag com did tell me that the value from the boost pressure sensor is lower than it should be.
Dont want to go replacing the sensor if it could possibly be the dump or the n24 boost control valve
This is all starting to get embarrasing at the traffic lights!

 

[dmjw01]

my car performs average for a period of time and then fab then goes back to average again.

This sounds quite similar to the problem with my remapped PD130. It'll run beautifully for a few days, then for no apparent reason it goes back to driving like a dog. Loads of lag (although the turbo does kick in eventually) and horrible flat spots through the rev range. It's also a bit "lumpy" and snatchy when trying to drive gently. I wish I could figure out the cause... MAF sensor is a prime suspect for me, but you've already tried that.

 

[sssstew]

I have a poor peformance issue with my cupra tdi
I have cleaned out the egr replaced the maf put forte throught the fuel system made sure the vnt rod moves freely and is not sticking, but my car performs average for a period of time and then fab then goes back to average again.
When its poor i cannot outrun a 120bhp astra cdti sri.
Its not overboosting does not go into limp mode but had vag com connected while i took it for a blast never throws a fault code up but vag com did tell me that the value from the boost pressure sensor is lower than it should be.
Dont want to go replacing the sensor if it could possibly be the dump or the n24 boost control valve
This is all starting to get embarrasing at the traffic lights!

so youve logged the boost and the requested vs actual is lower than what it wants?

 

[muddyboots]

What was the actual fault code in vag-com - "Charge pressure control - negative deviation", or something different ?

The negative deviation error is usually what happens when you get a boost leak somewhere (like a pipe popped off). It happens when the difference between requested & actual pressure differs by more than a certain amount.

However, if you got an error saying the MAP signal was too low or out of range, I'd have guessed that points to a faulty MAP sensor producing a signal that's complete nonsense. Especially if the performance comes and goes - if you had a leaky or disconnected pipe I wouldn't expect it to miraculously fix itself once in a while.

If it were me I'd try replacing the sensor. (Don't complain if you do & it doesn't fix it though )

 

[glynnd]

its coming to the point where i have got to start complaining. When its running fine i am getting 45 round town driving when its not i am struggling to get near 40. Checked all the boost hoses which are secure as i say replaced the maf and done everything obvious, to no avail.