I just noticed a very strange surging while driving, please help!

up4speed · Apr 26, 2018

My 2015 GTI has only about 7,700 miles and today I notices a strange thing. When I drove up hill at about 25mph under very light throttle, the car began to surge. It felt like the engine was being completely shut off (or throttle completely closed), then instantly turned back on for about 5 or 6 consecutive times, then it went away. It happened again about an hour later when I took the car back out. It's not like a bog, or losing power in one cylinder or anything like that. It's more of a stutter, like engine goes from completely off throttle to back on very quickly.
Any ideas on what to check? I have an OBDeleven, so I'm hoping that will help diagnose. Off the top of my head, the two possibilities that jump out at me are maybe the throttle position sensor is flakey or possibly the computer.

adam1991 · Apr 26, 2018

Coolant sensor, low coolant (causing the coolant sensor not to be submerged), or idle air control valve.

I'm guessing idle air control valve, but that's just a SWAG.

777-300ER · Apr 26, 2018

Did you get the suction pump recall done? Sounds like a loss of fuel. What was your fuel level at?

Adam those suggestions are just out of left field. A coolant temp sensor would not cause that in the slightest on an incline. These cars also do not have an idle air control valve having a fully electric throttle body and all.

up4speed · Apr 26, 2018

adam1991 said:
Coolant sensor, low coolant (causing the coolant sensor not to be submerged), or idle air control valve.

I'm guessing idle air control valve, but that's just a SWAG.

777-300ER said:
Did you get the suction pump recall done? Sounds like a loss of fuel. What was your fuel level at?

Adam those suggestions are just out of left field. A coolant temp sensor would not cause that in the slightest on an incline. These cars also do not have an idle air control valve having a fully electric throttle body and all.

I had the pump recall done.
I feel like these suggestions would cause the engine to "bog". In my case it seemed to go from full power to no power to full power almost instantly, a few times in a row. It's very strange, I never felt anything like this before. I wonder if it's that "fishbite" thing that happens when idling? Normally it doesn't happen when on the throttle, but maybe I was on it light enough to feel it?
I checked the throttle position parameters for about 5 minutes while varying, and holding pedal still, and the percentages stayed smooth when accelerating, and rock solid when holding still. It seemed normal to me. I attached photos of the parameters with the throttle off and fully depressed, can someone tell me if they look normal?
I'm not sure why there are 2 values for each. Does the potentiometer have 2 values, so there are no mistakes with calculating if the sensor gets flakey? Sort of like a check digit?
I was wondering why the 2 values for position 1 and 2 are basically the same, but the values for voltage 1 and 2 are very different.

Wrath And Tears · Apr 26, 2018

up4speed said:
I checked the throttle position parameters for about 5 minutes while varying, and holding pedal still, and the percentages stayed smooth when accelerating, and rock solid when holding still. It seemed normal to me. I attached photos of the parameters with the throttle off and fully depressed, can someone tell me if they look normal?
I'm not sure why there are 2 values for each. Does the potentiometer have 2 values, so there are no mistakes with calculating if the sensor gets flakey? Sort of like a check digit?
I was wondering why the 2 values for position 1 and 2 are basically the same, but the values for voltage 1 and 2 are very different.

Yup there are two sensors used to make sure everything is working properly.

The best way to check is to graph the voltages on the scan tool and watch for drop outs. They happen so fast you often won't see then if you are just staring at the numbers. I will say modern cars are pretty good about recognizing an issue with the pedal and storing a code, or even setting the CEL light.

Edit: I had included info about why the voltages are different, but then realized it was for older German cars and VW has changed things slightly.

up4speed · Apr 27, 2018

Wrath And Tears said:
Yup there are two sensors used to make sure everything is working properly.

The best way to check is to graph the voltages on the scan tool and watch for drop outs. They happen so fast you often won't see then if you are just staring at the numbers. I will say modern cars are pretty good about recognizing an issue with the pedal and storing a code, or even setting the CEL light.

Edit: I had included info about why the voltages are different, but then realized it was for older German cars and VW has changed things slightly.

Ok thanks! As long as the voltages seem normal, that’s really all I needed to know.
I didn’t get any error light, do you think I should still graph the sensor to see? Or is it basically impossible that it’s bad?
If so, I never did it with the obdeleven. How is it done? I figured I can drive around with the tool on until it stutters again. Is there any other value that I should graph that would be a likely cause?
Thanks!

up4speed · Apr 28, 2018

I put 32 miles on it today, and not a single hiccup. I’m starting to think it was that I was feeling the “fish bite” thing that it does when idling. I was under such light throttle and the engine was under load because of the hill (explains why it happened in same spot) so it was probably the same as idling, so I felt the bucking. I will report back if it happens again and I get a pattern. At this point I’m thinking it’s just a quirk of the car (fish bite issue every now and then).

demi9od · Apr 28, 2018

up4speed said:
I put 32 miles on it today, and not a single hiccup. I’m starting to think it was that I was feeling the “fish bite” thing that it does when idling. I was under such light throttle and the engine was under load because of the hill (explains why it happened in same spot) so it was probably the same as idling, so I felt the bucking. I will report back if it happens again and I get a pattern. At this point I’m thinking it’s just a quirk of the car (fish bite issue every now and then).

What RPM were you at? I think I know what you mean by fish bite. Motor and trans mounts exacerbated the little shake at idle. Raising idle by 50rpm mostly eliminated it though.

Sent from my LG-H910 using Tapatalk

up4speed · Apr 28, 2018

demi9od said:
What RPM were you at? I think I know what you mean by fish bite. Motor and trans mounts exacerbated the little shake at idle. Raising idle by 50rpm mostly eliminated it though.

Sent from my LG-H910 using Tapatalk

Maybe not exact, but it was around 2,000 rpm.

up4speed · May 8, 2018

Has been fine since that day. I'll just assume it was that "fish bite" issue and "normal".
If it happens again, I'll revisit this thread.
Thanks!

2SlowNoMo · May 8, 2018

were you in D mode or manual in too high of a gear for RPM? almost sounds like it was low idle stall out and re engagement.

up4speed · May 18, 2018

2SlowNoMo said:
were you in D mode or manual in too high of a gear for RPM? almost sounds like it was low idle stall out and re engagement.

I was in D mode, and it seemed to be about 2,000 RPM (out of memory).
I took the turn in very similar (or probably exact) way dozens of times since then (it’s in my neighborhood and it’s as I approach my house while “winding down”), and it has not happened since then. I honestlythink it was that “fish bite” thing since I was so light on the throttle and it was essentially the same as idling rough. Once you add the engine strain, it gives the impression of threatening to stall or surge.

Tigsel · May 19, 2018

You're obviously under warranty, why not let the dealer take a look?

up4speed · May 20, 2018

Tigsel said:
You're obviously under warranty, why not let the dealer take a look?

Why is that obvious? It's a 2015 that I purchased in December 2014.....warranty expired Dec. 2017. They had 3 year warranties back then

Plus it only did it once (one day) and it's hard to fix something that is not broken. They will just write on the paperwork "cannot duplicate, works as designed". I've been that route before with other cars. I checked if there were any codes, or pending codes with the OBDeleven, and there was nothing abnormal. That's all that a dealer would have done given the circumstances.

RRF985 · May 20, 2018

up4speed said:
Why is that obvious? It's a 2015 that I purchased in December 2014.....warranty expired Dec. 2017. They had 3 year warranties back then
Plus it only did it once (one day) and it's hard to fix something that is not broken. They will just write on the paperwork "cannot duplicate, works as designed". I've been that route before with other cars. I checked if there were any codes, or pending codes with the OBDeleven, and there was nothing abnormal. That's all that a dealer would have done given the circumstances.

Powertrain is 5yr/60k on 2015s.

I just noticed a very strange surging while driving, please help!

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