Excessive Slowing Down Without Using Brakes

[Marteh]

I have owned my N/A R34 4 door for approximately 11 months now and in the past 1 month I have seen a significant change in how my car is running.

I have noticed that when completely letting go of my accelerator on a flat road, the car begins to brake quite quickly without any coasting sensation you would expect.

Even when going down a hill, (for those of you on the north shore in Sydney, the big dipper on the F3 near Mount Colah) I need to have my foot on the accelerator to keep it from dropping below 110km/h (whilst having momentum GOING DOWN A STEEP HILL)

The only modifications which have been made over this time period (and or 2 months before noticing a problem) was the installation of a 2.5" catback exhaust, and replacement of coilpacks and spark plugs.

It is obviously a very uncomfortable feeling and uneconomic when my foot needs to be left on the accelerator when otherwise, I could simply have the foot off and be coasting. In the meantime I have been shifting to neutral (I should have noted the transmission is tiptronic) to attempt to save fuel.

The uncomfortable and annoying "self-braking-problem" seems to be due to the revs not dropping instantly when taking the foot off my accelerator, it will instead drop from whatever revs i was on to 2k slowly creep down from 2k - 1.1k and feel asif a great load is on the gear. When changing to neutral immediately after letting off the accelerator, the revs drop to ~1.1k, 1k and obviously not being in gear, I can coast comfortably.

the only reason I am posting is because I know that my car was performing differently with the ability to simply coast, without going from 60km-40km in 2 seconds on flat road and momentum.

I would REALLY appreciate any insight or help into what the problem may be!

lack of backpressure to the engine?

limp mode for some reason?

[116.hks]

Could be a seized calliper, not realising the pad from the rotor. Can't see any other problem. Does the car run ok and idle ok besides the fault you have.

[Marteh]

Its actually funny that you mention that.

I'm not exactly sure what a seized calliper entails however..

my front left wheel squeeks about twice per rotation WITHOUT any brakes applied, this may be the problem area, this could be some point of contact?

Once i begin to brake the squeak dissapears (I assume its not a brake pad problem since squeeling you hear from the wheelswould occur WHILST braking, but this isn't the case for me)

Other unique feelings I have when lightly pressing my brake say at 60km/h is a subtle back and forth motion, maybe indicating that the brakes are grabbing/letting go, grabbing/letting go (case of warped disc brakes?) Once I apply more pressure to the brake the pads come into complete contact with the disc and the feeling of braking is smooth. I have NO vibration in my steering wheel while braking, just to clarify.

So I now might have two problems.

Do any of these symptoms sound familiar?

[PM-R33]

Jack up the car and rotate each wheel with your hand. Each wheel should rotate fairly smoothly and only just be touching the brake pads. If one or more wheels feels a lot tighter than the others than you know you have a brake caliper/brake rotor issue.

[jiffo]

You say that you need to select neutral for the car to freewheel as it used to do.

If neutral fixes the problem, it's hardly going to be a brake issue is it.

Take the thing to an auto specialist. One quick test drive and they'll diagnose any transmission issues.

[mad082]

yeah if putting it into neutral makes the car coast just fine then it is more than likely a gearbox issue (won't be brakess). may be low on fluid, the fluid is in need of replacing, or the gearbox may have an issue.

[Marteh]

That seems logical, as the car coasts fine whilst in neutral.

To be absolutely certain, I will take it to be checked out, and tell you how it goes! Thanks for the insight.

[Iron Chef]

Sounds like the torque converter isn't locking up.

[PM-R33]

Ah ok I didn't read the neutral thing, I just skimmed over it.

[Daleo]

Putting your auto in neutral whilst doing 110km/h is one of the best ways to destroy it.

Oil pressure is what keeps the transmission alive, the faster you go the higher the pressure. So what you're doing is effectively running you auto at idle oil pressure, (the pump is on the converter side), but you're spinning the internals at 110km/h, because it is locked to the tailshaft. Low pressure equals failure.

Get it to an auto specialist before you damage it any further.