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Discussion Starter #1 (Edited)
Engine flat spot with 1.4 TDI

Hi guys,

I'm encountering an issue with my 1.4 TDI engine (year: 2000), where the engine power drops by around [what feels like] 20-30% when I hit 30-40k revs in 3rd gear. This only seems to occur when accelerating from around 30mph. Turning the engine off and back on again solves the problem. If I leave the engine on, the problem never goes away... Sounds like the engine management system? The issue isn't intermittent and is fairly straight forward to re-produce.

First attempt at a fix was to do a full service, which improved the overall performance by around 10% but the issue still remained.

I have just had the exhaust system replaced, which seems to have increased the overall performance by around 30% (in terms of acceleration), and the flat spot issue occurs far less often. Also, we can now actually hear the turbo whistle now (when the revs rise above 20k), which to me suggests that the turbo may not have been performing correctly before - correct?

Originally, my theory was that the engine management system was disabling the turbo due to poor engine performance -- but now that I can hear the turbo, and it still whistles after I hit the flat spot, this makes it seem that it's not an issue with the turbo. Now, I'm thinking that the engine management system is reducing the engine power. However this theory is based on absolutely no knowledge of engine management systems.

Should I just take it to a VW dealer and damn the expense, or is it worth attempting more fixes? A friend of mine said he had the same issue, and it turned out to be a dodgy valve.

Before I had it serviced, I took it to a garage with a diagnostics machine. They said the car was reporting no faults. So either the fault code only appears when it occurs (and before the engine is reset), or the fault is not reported at all. Perhaps I need to take it to a garage with a rolling road, so they can reproduce the fault *while* it's plugged into the diagnostics machine.

Cheers,
Nick
 

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Discussion Starter #2
Here's the VAG-COM result:

Code:
VAG-COM Version: Release 409.1-US


Chassis Type: 6N - VW Polo
Scan: 01,02,03,08,15,17,19,25,35,41,45,46,55
 
-------------------------------------------------------------------------------
Address 01: Engine
   Controller: 045 906 019 
   Component:   1,4l R3 EDC 0000SG  1040
   Coding: 00003
   Shop #: WSC 00788
2 Faults Found:
17964 - Charge Pressure Control: Negative Deviation
            P1556 - 35-10 - - - Intermittent
17664 - Shareware Version. To Decode all DTCs
            P1256 - 35-10 - Please Register/Activate - Intermittent
Readiness: N/A

-------------------------------------------------------------------------------
Address 03: ABS Brakes
   Controller: 6X0 907 379 B
   Component: ABS     30 IE CAN  V004
   Coding: 05603
   Shop #: WSC 00788
1 Fault Found:
00290 - ABS Wheel Speed Sensor: Rear Left (G46)
            35-10 - - - Intermittent
 
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