Seat AHU No throttle woes

[MaroonCordoba]

Hi! Hoping someone can help…. I have a ‘98 Seat Cordoba with the 1.9 TDI, I believe it’s an AHU, 90hp.
I had an intermittent issue that just got less so… and maybe easier to diagnose. After several spurious observations I have pinned down the following:

- starts as normal. If driven immediately it drives fine
- if left to idle, or if the accelerator is released for more than a few seconds when driving it enters a ‘limp mode’. Rpm is a steadyish 1200 and the glow light starts flashing after a couple of minutes. Throttle unresponsive.
- Stopping ignition off for a couple of minutes and it has ‘reset’. But it needs a couple of minutes.
- I have two switches on the brake pedal (and one on the clutch?!). The fault is the same with either or both switches disconnected. Also same with the non-brake-light switch bridged.
- when first started the engine will still rev with the brake pedal pressed. When driving if the brake pedal is pressed sometimes it cuts the power, sometimes not.
- if the accelerator pedal sensor is disconnected and car started the revs rise to 1200 almost immediately, if connected it takes maybe ten seconds or more for this to happen.

I’m thinking it’s either an issue with the pedal sensor, or the ECU but would be really grateful for any pointers. After changing numerous air flow meters, and a few months ago a crank position sensor I vowed to go down the MTDI route…. But if I can fix it….

Thanks in advance!

 

[Seatman]

I had a 2000 plate cordoba with the AGR 1.9 tdi lump, loads of problems with the throttle pedal sensor.

Check the ecu, open it up and see if it's soaked. Mine was, a white sort of corrosion collected on the board where the connectors for the plugs came in and was actually causing the pins to short out. I cleaned it all up, dried it thoroughly in a warm space then put it back together using clear silicone sealant. Never had the issue again.

Ecu sits in a stupid spot at the bottom of the windscreen and catches all the rain run off.

 

[MaroonCordoba]

Hi Seatman, many thanks for your reply. I wonder if your ecu and mine are the same - mine is all cast alloy with the end where the connectors and vac pipe are, held on with four torx screws?
As you say it’s in a stupid place, and the fixing screws are accessed from inside the car I think? - that looks to be the hardest part!

 

[Seatman]

Can't remember now exactly how mine was but defo got it from outside. I'm sure yours will be accessed from outside too.
Is it maybe in a cage/frame and you have to bend tabs at the sides to release it then it slides out?
Tbink mine was.
My ecu would've been newer than yours with the separate pressure sensor. Same idea though, cast casing held together with torx and usually some sort of bonding material.

 

[MaroonCordoba]

Many thanks. My ecu looks to be secured by two screws but you can see the threaded ends under the bonnet, so the heads must be inside, under the dash. Annoying!

Was yours really intermittent? I just drove maybe ten miles and it was fine till I was five minutes from home. Yesterday it was virtually undrivable!?

I can’t figure out the relationship between the brake pedal and the throttle response, it behaves differently if the car is in gear or stationary or coasting. And seems somewhat erratic. To be fair I never paid much attention so I’m not sure what is ‘normal’ for this car.... or if it has any connection with the fault.

As I think you suggested, my ecu has the pressure sensor inside it. I will dig in but am trying to locate a backup car first!

 

[Seatman]

When you press the brake pedal it cuts the throttle but maybe the signal for the throttle is weak at best so when the ecu cuts the throttle after pressing the brake it struggles to read the signal again. Just a guess.

Mine started as intermittent then got worse till eventually the throttle disappeared altogether

Post 4 in another thread I found, 1998 ibiza, ecu held in by some tab he had to bend out the way, I'm 99% sure yours is the same and you don't need to undo any screws.

 

[Nevada_TDI]

I may have missed something... you say you bridged the brake pedal switch, I will guess the switch is NO, did you double check the clutch switches too?