Per the title, four times in the last week or so I have almost had a minor bingle when the engine surged just as I was coming to stop.
Only ever in Drive, not (yet!) in reverse.
Just as I am about to stop, doing no more than 2 or 3 km/h, and I have eased off the brake pedal such that I am only lightly pressing it, the engine has suddenly and unexpectedly surged to around 3,000 rpm and thrown the car forward, overcoming the brakes.
Each time I have had to slam the brakes on hard to stop the car from running into something.
The first time it happened in a supermarket car park I nearly hit the car next to me and it scared the hell out of me!
And no, it is not caused by my right hoof slipping off the right side of the brake pedal and onto the go pedal.
It doesn't happen every time, say one time in 20 I am pulling up to a stop, but it's getting to the point of being dangerous especially with cross traffic.
I have no clue what could be the cause.
Maybe the throttle butterfly sticking open???
Maybe the VAP tune has gone a little haywire???
Help!

 

I would love to hear some ideas as to what痴 causing this. My car does this about once a month. I haven稚 been able to get it diagnosed due to how infrequently it occurs. Like the OP, I知 definitely not slipping my foot off the brake. It goes away as soon as I give it some gas, and doesn稚 show up again for a few drives. Very frustrating, and no CEL or codes being thrown to help diagnose.

 

Same here with the codes, each time it has happened I have checked for codes first chance I got and nothing, not a single code.

 

AJ,
Do you have a VAP tune?

Oz,
Revert back to the OEM tune to see if it still happens. If so, it痴 an unrelated system issue. If not, reload the VAP tune to see if the software reload solves the problem.

 

Hey Unhinged,

I知 100% stock still. Been holding off installing my VAP tune until I sorted this out.

 

I have a couple other mechanical gremlins, but I don稚 think they池e related at all. Some backlash in my diff that the dealer wouldn稚 address, and once in a while I can smell some coolant after a spirited drive.

 

OZ, AJ
Do you happen to notice if the RPM's drop a little lower than normal right before the surge ?
The reason I ask is I had a GT that did as you described and it was the Throttle Position Sensor was loosing signal when close to the idle position. The lower than normal RPM was barely noticeable before the big surge.
Initially the fix was a recalibration which worked for several months but after it started happening again the TPS and throttle body were replaced.

 

Only one teensy weensy problem with reverting back to the OEM tune - I have the larger crank pulley so I would have to creep along like a tired snail (just like 99.99% of Adelaide drivers) for ages waiting to see if the problem occurred again - no thanks!

 

Nup, no drop in RPM that I can recall.
Not to say that didn't happen, just that I never noticed it and I'm usually very attuned to that sort of thing.

 

Just keep it under 5000 rpm (I know, self-discipline is difficult when you池e in the F type) when WOT.

 

A few things could be happening here:

1.) TPS as mentioned could be going haywire.
2.) Long shot, but the supercharger should be opening the bypass on decel like that, is it sticking closed and dosing the engine with some boost?
3.) Does the vehicle have auto stop/start and the starter motor is kicking the engine thinking you've stopped and are restarting? I only suggest this because of your description of the brake pedal usage.

 

1.) Yes, that's a possibility, although I would expect to see one or more codes if this was the cause and there are no codes.
2.) Yes, another vague possibility. I forgot to mention before that a couple of days before the first hiccup I poured a can of Oxicat in the fuel tank. This is an O2 sensor and cat converter cleaner, see here for example: https://www.autoprofishop.us/store/p...Cleaner.html#/
I have used this product several times before on the XFS (diesel) and XFR and once on the F-Type about two years ago and never had a single problem. Maybe just maybe this time it did something to the SC bypass valve?
3.) No way, I disabled the SS from the get go and completely removed the second battery a few months ago.

 

#2 is looking like a possibility. It is very possible to have some O2 issues without quite triggering the CEL. To check, you could see if you could real time log your O2's to see if they are acting up, but just not to the point of a CEL?Worth checking. Also, may clear itself up as this stuff burns off?

Good luck,
DC

 

Your last sentence is what I am hoping for, expecting is putting it too strongly.
All my driving for the last week or so has been short trips with 15 km the maximum distance, so even after filling up a few days ago (from half full when I put the Oxicat in) I don't think I have yet burnt off all the Oxicat. I give it another two weeks before it's all burnt off and then if it happens again I will start to panic!

 

Not a single code was thrown when my GT's TPS was acting up. Luckily the Technician had seen the issue before and went strait to it.
Did AJ also add any cleaners or stuff to his fuel system ?
Oz, maybe an extended road trip that avoids congested areas could quickly get you through your current tank of fuel ? Of course being out in the boonies with a car that you don't have confidence in would be a deterrent.

 

Hey madmax,

No fuel cleaners used here. I was planning on running some through to see if it made any difference, I get a rough idle once in a while and was thinking this could help out. Btw my car is stock and around 30k miles, so I知 hoping no major issues are popping up.

 

Could it be Gearbox related? does this happen in auto mode only? maybe the car is shifting down from 2nd to 1st improperly, causing the spike in RPM and making it Lurched Forward. I know in manual mode if I'm slowing down and I'm in 2nd and occasionally when I shift into 1st it'll cause the car to jump a little bit.

 

Not certain, but from your description it sounds like your issue is different than OZ? Sounds like you have random rough idle, not surging when coming to a stop? Or maybe I am misunderstanding.

Typically, if you are having a rough idle (like the idle is searching around where it should be smooth), the easiest and likely best place to start is to clean the throttle body, to make sure the edges seal properly when the plate is closed. You can use MAF cleaner and/or a clean rag to get the gum off of the edges, and it is amazing how it smooths out. I do this a lot on the Porsche 997 TT and have started it on the F-Type R as well. See picture below for reference. Cheap and easy to try...

DC

 

I値l clean out the TB and see if that helps.

My surging typically happens when I知 already at a stop for a 30-45s, and I値l feel it slowly start to build up, requiring me to hold the car with the brakes slammed down, or hopefully I知 free to accelerate and the problem goes away.

 

Typically the issue with throttle position sensors (as well as MAF and MAP sensors for that matter) is that *they* don't know there's anything wrong with them, and thus won't set a code. With a MAF it's easier to check because the car will run with it disconnected, albeit throwing a light and not running optimally. A TPS can't be checked any other way except for voltage/resistance at the sensor itself as far as I'm aware.