Fix Error 00777: Strange Effect? (Solution)

Hello everyone, first of all,

After reading the community for a long time, I've finally joined, mainly because of the significantly higher level of discussion compared to other forums, and currently, I'm looking for answers to a question that has become very interesting to me. Here's the story:

Last week, I got stranded on the highway. While driving with the cruise control activated, suddenly everything went haywire (ABS+ESP light came on, preheating indicator blinked), there was no power, and the idle speed increased. I took my laptop from the trunk, found error code 00777 in the error memory (Electronic Throttle Control, signal not plausible, intermittent), and drove it to the workshop. They searched for it until evening (of course, it was Friday) but didn't find anything. On Monday, I picked up the car - suddenly everything worked again. They did a test drive and checked the signal from the Electronic Throttle Control - everything was OK. Now, today, the same thing happened again: loss of power while braking on the highway exit (again, 0 throttle given at the moment the error occurred) - luckily, it was right in front of my office with an adjacent industrial hall .
So, after reading the technical article, I opened all the connectors, treated them with contact spray, and cleaned them thoroughly. Then, my curiosity got the better of me, and I disassembled the accelerator pedal. I worked my way up to the potentiometer, and after reading about the Hella issue with corrosion, I also cleaned its surface with isopropyl alcohol. I reassembled everything carefully, adjusted it properly, and now – the car runs like a dream again.
Okay, here's the strange effect that I simply can't explain:
'For about 20,000 km now, I've noticed that the engine idles roughly when it's warm. According to VAGCOM, the injection timing is at -0.4° BTDC (Before Top Dead Center). About a year ago, the workshop adjusted something, and it was slightly better then, but it didn't last. Now, after disassembling and reassembling things today, the rough idling is completely gone?! What does the electronic throttle have to do with idle? Or could it be that the idle contact (which now cuts off at about 5% throttle, hopefully that's okay) was loose?'

Good evening.

Michael.

P.S. What I find very amusing is that with error code 00777, I always get another error in my ABS control unit. I don't know the exact number, but it says something like 'Throttle potentiometer, measurement not plausible' or similar, and it comes from the MSG. Could it be possible that they actually installed a throttle valve in my diesel engine or that the message from the MSG is being used to turn on the lights...

Hi there,

The accelerator pedal, or throttle body, has an idle switch. This means that when you don't press the accelerator pedal, not only is the potentiometer at its end position, but also a contact is closed, which tells the engine control unit (ECU) to initiate idle mode.

I can imagine that there might have been a glitch here, which is why it was causing the stuttering. In any case, that would explain why this issue disappeared after your cleaning process.

Contact spray isn't actually a good idea, especially for the gas stove, because it can cause a similar problem to what you described. The engine control unit is very sensitive there and can quickly go into emergency mode. In my case, even a small amount of moisture in the connector caused it to constantly enter emergency mode.

Best regards,
Gunnar

Hello Gunnar,

Of course, I didn't spray the contact cleaner directly onto the potentiometer – it looked too delicate for that – but only on the contacts. Then, I dried it gently with warm air. In my experience (older stereo systems also have these 'cheap' carbon tracks), isopropyl alcohol works quite well to verschandeln potentiometers.

Best regards,

Michael.

Hey guys,

It was really strange for me too:

In the early morning at 6:30, I got into the car and started driving towards work. Then, after about 2 kilometers, suddenly it wouldn't accelerate anymore , and the idle speed was 1300 RPM .
Rolled onto the parking space, connected the diagnostic cable, and read the error memory. -- Error code 00777 (a common one), but the gas percentage readings in the data blocks are perfect, ranging from 0% to 100%.

"Oh crap, I thought to myself, now I'm going to be late for work again!! So I started driving towards work at about 1300 RPM and then realized that I could still accelerate using the cruise control lever?"

So it seems the engine is not in a limp mode }.

After work, I was actually looking forward to tinkering and troubleshooting, but then this happened: I got in, started the engine, drove 100 km, and there were no more issues!
It's been two weeks since this happened, and the error hasn't occurred again yet.

Was a potentiometer issue causing the problem (perhaps due to condensation or something similar)?

What can I do proactively to prevent this from happening again? Do you have any other tips?

Thank you.
Greetings (and happy Father's Day to all the dads)!

Frebert.

frebert wrote:

This has been happening for 2 weeks now, and the error hasn't occurred again since then. Was a potentiometer issue causing the problem (perhaps due to condensation or something similar)? What can I perhaps do preventatively, or what should I look into to make sure this doesn't happen again? Do you have any more tips?

The engine control unit (ECU) expects that when the pedal is pressed, the idle contact will open or close within a specific PWM voltage range (approximately 10%, if I recall correctly). Otherwise, an error will be detected.

For continuous monitoring, you could temporarily connect an LED to the signal from the idle contact. If it behaves unexpectedly at some point and the engine reverts to emergency mode, you've likely found the cause.

Hi Ulf,

Thank you for the quick response.
Is there no bit pattern in VAG-COM that allows you to see the idle speed sensor?

Greetings.
Frebert.

frebert wrote:

Is there a bit pattern in VAG-Com where I can see the idle speed switch?

In the Golf 3 AFN, it was the middle bit (of a byte) in field 3 of module word block 2.
Conveniently, field 2 displayed the percentage value of the PWG.

Yes, that's right, I remember. But it also fit the requirements! Specifically, the "%" in field MWB 2 and the "1" in field MWB 3 of the pattern.

As soon as you press the accelerator a little, the 1 Series transforms into a zero (meaning it becomes very fast).

I believe it was actually a settling issue or a moisture problem.
Apparently, the engine control unit (ECU) is said to be very sensitive to such things, according to other posts in this forum.

Thank you for your help.

Greetings.
Frebert.