Low Boost! Running Out Of Options... Please Help

[mrchipz]

1.9 TDI 115 AUY engine 190k. EGR blocked off. Intake and EGR valve cleaned.

Been having limp mode issues for a while.

Did have sticking vanes. Turbo stripped and cleaned. VNT now free.

MAP and MAF sensors replaced.

Tested for boost leaks. Only slow gradual loss from 2 bar as expected.

Vacuum pipes either side of N75 valve holding vacuum. N75 also replaced.

Actuator has full range of movement by vacuum.

Limp mode is triggered by asking for moderate acceleration around 2000-2500rpm.

Light throttle through that rev range doesn't trigger.

Full throttle above 2500rpm or below 2000ish doesn't trigger.

Turbo shaft has very slight play.

I'm thinking turbo just knackered but then it works well above 2500. Still getting 45mpg.

Any suggestions appreciated.

[insanitybeard]

Intermittent fault/ dirty/worn contacts on the throttle position sensor on the throttle pedal?

Has it registered any fault codes?

[Scorpiorefugee]

I think a bad throttle position sensor puts the engine into a constant 1100 rpm mode - which can be damned dangerous if it happens while overtaking! As far as I know it is the only cause of this particular effect. I've had this several times and cured it by stripping and cleaning - carefully.

 

If it does happen at an inconvenient time and you have the presence of mind you can leave it in gear and switch off and on quickly and you are away again without stopping. Just don't let the steering lock activate or you will be in serious trouble. :wacko:  :wacko:  :wacko:  

Edited August 18, 2014 by Scorpiorefugee

[xavier]

Note on the switch off and on, if it's dark and you're headlights are on, they will go out when you switch off (as I found out once!)

[Scorpiorefugee]

That headlight problem cannot be as bad as our Picasso. The rotary light switch is on the same stalk as the dip/indicator lever with the pip in such a position that if either is operated slightly off centre the switch rotates and all lights go off which can be terrifying if it happens as you dip the lights on a dark country road approaching a sharp bend. Not too bad the second time but the first time......... :28:

[alan_131]

If you've got vcds lite have you tried logging required vs actual - just in case engine management is throwing a wobbly?

[cyborg]

Check FAQ number 74 in help section