Tdi not revving above idle

[tan159753]

Just bought the car, Toledo Tdi 1z engine.

First day 1 hour drive car is as good as new. No stutters or performance problems.

Second day car drives fine then after about 1 and a half hours, travelling on the motorway in fifth, lifted my foot off the accelerator when a nutcase doing 55mph in the fastlane and not letting other traffic through so had to slow down. When I put my foot back on the accelerator, engine wouldn't rev for a second then got worse. This continued to gradually get worse talking longer and longer for car to rev again until about half an hour later, engine starts to splutter and when foot was lifted off the accelerator and put back down again, nothing whatsoever.

Pulled over for 1 hr to let things cool down and then managed to get revs up by keeping accelerator half way down for about 30 seconds then car will rev freely until I take foot back off accelerator completely then It refused to rev at all until left to cool down.

What could this be? No smoke whatsoever and whilst it is revving, seems to pull ok.

 

[enigma]

Sounds very similar to the problem i had with my arosa.

Complete shot in the dark but with mine it was the EGR valve that had gone.

Worth a shot maybe?

 

[tan159753]

Why would a duff Egr cause accelerator to die completely?

Yesterday when the accelerator dies it happened after about 90 mins of driving. Today I drove the car for 1 hour from cold and it drove fine.

 

[enigma]

on its way out perhaps?.

im not sure jsut saying it does sound familiar to the problems i had.

 

[thesonny]

sounds exactly like the problem i have with my toledo. which was caused by the lamba sensor and the MAF combined. Which could explain why it only happens after and hour or so due to the exhaust getting hot and the lamba sensor overheating possibly?

 

[sssstew]

diesels dont have lambda sensors.

 

[thesonny]

well i went for petrol engine reasons as i have never owned a diesel. my bad!

 

[tan159753]

Have just found something else out.

There is a big 50 amp fuse in the relay/fusebox under the steering column (a little above the 109 relay) in the car that was blown. Overwhelmed with excitement at finding such a big thing, I ripped the old bugger out and swapped it for another one. Rushed to start the car expecting it to be back to its good old self again but the problem was still the same. Starts but would not respond to to the accelerator at all. NO DARN REVS!!! Kept tring for the next half hour. Nothing.

Figured that since the problem only occurs when travelling for nearly 2 hours, I then decided that something is probably heating up and so opened windows fully, turned off heating and put fan on full blast to cool down inside of car to cool down any electrical gremlins. Since I was 100miles from home and it was getting qute late, I decided to drive car back with engine only idling and managed to reach 45mph in this condition. However a few minutes into the journey with fans still blaring cold air out and inside temp really coold, the throttle slowly came back at which point I managed to drive the next 2 hours problem free.

Questions are:-

a) What was the big 50 amp fuse for inside the car? When it was blown I didnt notice anything out of place, except the obvious throttle problem.

b) If the fuse was related to the throttle problem, why didnt the car return to normal immediately after changing the fuse. Does the ecu slowly reset itself after a while?

c) How do you manually reset the ecu without VAG-COM? I hear of some people say disconnect the battery for 30 mins but what exactly does this do? Does this clear any fault codes stored?

d) Do you think it could be an electrical problem (relay or throttle position sensor heating up) that went away when I cooled the inside of the car down? Or did I just freeze my nuts off for 2 hours for nothing. Reason I ask this is because the problem only comes after a couple hours of driving. Ok for normal everyday driving but id like to fix the car before my next long journey.

Please help. Replies would be much appreciated.

 

[silver surfer]

these engines are fly by wire throttle which is situated in the drivers side footwell quite close to the heater it could be that .when it gets warm is starts to break down and you loose throttle best way to find out is to have fault codes read to see what the fault is

 

[tan159753]

The problem went away by itself back in February when i let the inside of the car cool down. Unfortunately now it is back!! Car had been fine for 10 months, used daily. Now accelerator doesnt work at, whether car is cold or hot.

VAGCOM gives the code "00777 (G79) throttle position sensor too high". However when reading the data blocks for throttle position, it seems ok. Starts at zero and goes up accordingly to how much i press the pedal and at full throttle shows 100%.

I have changed the sensor at the pedal with a known working one and cleared the code, still the same. Will try a maf now.

Lots of googling and searching in this site too reveals that this problem is common but nobody has revealed any fixes.

Any other ides?

 

[silver surfer]

http://www.tdiclub.com/ try this they will possibly know

 

[tan159753]

That a great site - a wealth of information, after this one of course

Found loads of people there with exact same problem, same fault code, random like mine too but funny enough all had different fixes:-

First person fixed his by cleaning battery terminals and ground
Second changed his MAF
Third guy changed little pipe in ecu
Fourth only cleared the fault and prob never returned
Fifth changed the throttle position sensor
Sixth changed both brake switches

I tested both brake switches via vagcom and both seem to be working but what i've now found out after hours of studying technical drawings is that if the clutch is pressed, the engine wont revv either.
When testing the brakes i got 1 0 0 when the brake pedal was not pressed and a 1 1 1 when brakes pressed. I am guessing the first digit is the clutch pedal signal and it always remained a 1, ie pressed condition. Cant wait till the morning to check the clutch switch. Will let you know.

 

[tan159753]

Well guys, the Almighty (if you believe in such a thing) has finally put me out of my misery. I have finally fixed my car!

To be honest I am not 100% sure how i fixed it. I took the ecu off the spares car which was in far worse condition and tried it in my car. The ecu numbers were all exactly the same but when i tried to start the car it would start but then immediately stop. Obviously the spares ecu had to be matched up to the immobilser. I couldnt be bothered doing this at the moment so decided to put back the original ecu. Although the pins on the original ecu were in very good condition with no obvious signs of rust or oxidation, I decided to give them a quick brush over with a wirebrush then smeared Silicon Grease over the pins. Put it all back together and bingo. Problems over. Dont know if this was the problem or the car decided to feel pity for me. But its fixed now.

Although the throttle sensor is connected to the brake switch, it didnt make any difference in my car. The switch is normally closed nd goes open when brake is pressed. My car actually revs ok either with brake switch on or off. Only difference is the glow plug light flashes constantly when brake switch is left disconnected. My car is one of the first TDi's and its functionality may have changed in later models.

On the bright side, in trying to fix the car, I have fixed a multitude of potential problems that definately would have given me problems in the near future. In short, anyone with this problem should


1) check, no CLEAN all grounding points. In particular the one near the ecu and underneath the battery.

2) Change all vacuum pipes, especially the one going to the ecu and also the litle one inside the ecu.

3) while it is out, clean the pins on the ecu irrespective of how good they look. Silcone Grease ie CAGE mod is a good idea

4) Check or change both brake switches.

5) Change the throttle sensor if none of the above fixes.

I would like to thank everybody that took the time to listed to my problem and give some good responses.

 

[NeilMcK]

Mines died on the M6 today, touched the brakes (out of cruise), pressed the throttle, nowt, then flashing glow plug light.

Limped off the motorway and got a tow.

Garage says the ECU is saying faulty throttle position sensore on the pedal. It may be right, since the light doesn;t flash until you press the throttle a few times.

The first thing they checked was the MAF, and connectors. A right pain in the arse, especially as my car is in Wigan, and I'm in Bristol. Grrr.

 

[NeilMcK]

Update on the issue. It turns out that there was nothing wrong with the throttle pedal.

There are switches on the brake and clutch that link in with the cruise control & electronic pedal.

The dealer says it is common for these to fail, and they have been redesigned to cure the problem.

They knew what the problem was and the fix immediately.

Cost of parts, £11.

So, I'd try that first before stripping things down.

Car hasn't so much as coughed since.

I hope this helps anyone searching.

Hope this

 

[NeilMcK]

Update, same thing happened AGAIN!

Obviously not the switches.

Will try other fixes mentioned.

Bugger.

At the point of handing it back to the garage and saying fix it or don;t give it back.

 

[tan159753]

heh Neil, have you VAGCOMed the motor? If so what is the code and FULL description that comes up?

Since my last post, the car ran OK for 3 weeks then 2 days ago WHAM. Same problem. Luckily I have managed to find the real problem now and have fixed it hopefully for good. Wasnt the ecu after all.

Where are you based?

 

[NeilMcK]

yep, the fault is :

18047 - Accelerator Position Sensor 1/2 (G79/G185): Implausible Signal P1639-35-00--Readiness: N/A.

It was in the dealers today and they called up to ask if it happened during or after rain. It had, so they said it was water ingress above the pedal, causing the fault. It's where teh loom passes through the bulkhead. The garage wanted £260 to do this, but the garage I bought it off can do it for free since I've only had the car a month.

It could be that, since the car works ok if left for a while.

What did you do?

I'm based just outside Sirling btw.

Neil.

 

[tan159753]

so they said it was water ingress above the pedal, causing the fault. It's where teh loom passes through the bulkhead.

Neil.

I doubt that unless you get bucket loads of water in your footwell. I had a good look at my Throttle sensor and there are no vents for water to get in. Its pretty much a sealed up unit.

The problem in my car was the brake switch, not the one used to control the brakelights but the one thats connected to the ecu.

The Boring Bits
In fact the way it works is the ecu sends a signal out to the brake switch. If the brakes are not pressed, this signal goes onto the throttle sensor and the ecu is happy to keep the fuel coming. When you press the brakes, the ecu automatically cuts the fuel to a minimum. When the brake switch goes faulty and the contacts inside the brake switch don't make a good clean 100% contact, the throttle sensor doesn't get the proper signal its supposed to see and so the ecu cuts the fuel as a safety measure and sends the code

Implausible Signal P1639-35-00--Readiness: N/A
Neil.

meaning "I see a signal but it nonsense"

When I changed the brake switch and started my car, I didnt get any response from the accelerator straight away. I had to drive the car for about 2 minutes before the ecu realised that the signal to the throttle is now good and consistent and the engine then started to respond. Now its brand new.

I would get the garage to take the brake ecu switch off and put a multimeter on it. It should read 0 ohms or 0.2 ohms max. Mine was reading 2 ohms and although that is effectively good continuity, it wasnt good enough for the ecu. If the switch is ok, tell the garage to disconnect the wiring at the ecu itself and inspect the pins on the ecu and the little spade connections on the connector. If you see and signs of rust or green oxidation, they will need a clean.

Failing that it might be the throttle sensor itself as they can go bad but not very often.

 

[NeilMcK]

I'm just going by what they said. They said that water is getting in around the connector block and they will re-seal it. they said water is getting into the loom.

I might try myself with a watering can tomorrow, just to check.

I tried a quick experiment tonight, foot on brake (in neutral) and try to rev engine - no revs, release brake and it revs ok. The first garage to have a go did change the brake switch & cluth switch as suggested by Seat.

I do agree though, if it's not the water then it has to be either the wiring to the ecu from the pedal or brake, or the pedal sensor itself.

The technician at Seat said that this was a relatively common fault, so fingers crossed. If water is getting in to the loom then it's no bad thing to seal it up in any case.

My only thought is that it has been p**sing down recently so I'm not sure why, if it's water, it takes so long to fail. Maybe a combo of water & motorway speeds.

The fact that it clears after a while would suggest that it is a heat related issue, which would point to the pedal going faulty.