Car doesn't decelerate properly?

Forziii · Postby **Forziii** » Sat Jan 30, 2016 8:32 pm

Hi everyone,

My girlfriend has an NB (I think it's a 2003 model) and it has a couple of small issues which I think are related to the same cause.

1. When cruising (car warm or car cold) and you let off the accelerator, it feels like the accelerator is still pressed slightly, as the car doesn't slow down/decelerate like i think it should. It pretty much ALMOST keeps a constant speed on a flat straight. It occasionally decelerated for like half a second every few seconds during this weird time...
I would usually assume that it's a throttle body issue, but when i push the clutch pedal, it drops to idle like normal... (which imo also rules out iacv issue)

I think it could be an air leak somewhere which worries me if it's causing the engine to run lean, but i'm not 100% sure.. has anyone experienced this?

2. When the car is cold (rarely when warm) and you accelerate (not hard acceleration, just the usual acceleration when the car is cold) it seems to be inconsistent in it's acceleration.
The car accelerates as if you're slightly opening and closing the throttle when your foot is dead still.

I can post a video of how the car doesn't slow down if i'm not clear enough in my explanation or if it would help.

Any help/advise on things to check is much appreciated.

smy0003 · Postby **smy0003** » Sun Jan 31, 2016 9:04 am

Check the throttle cable and assembly on the throttle body to make sure it's not binding.

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Steampunk · Postby **Steampunk** » Sun Jan 31, 2016 2:47 pm

Does it have cruise control?

project.r.racing · Postby **project.r.racing** » Sun Jan 31, 2016 4:19 pm

It is auto?

davekmoore · Postby **davekmoore** » Sun Jan 31, 2016 7:00 pm

What happens if you put your toes under the throttle pedal and lift?

Forziii · Postby **Forziii** » Sun Jan 31, 2016 8:15 pm

It's not automatic
It doesn't have cruise control
I'll have to check about trying to pull the pedal back after letting off, but it doesn't seem to make sense since If it throw it into neutral during the time where it's not slowing down, it drops to regular idle.
Thanks for the quick responses. I will get back to you when I get more info and I will check out the throttle cable etc again, but pretty sure it's ok

Forziii · Postby **Forziii** » Wed Mar 02, 2016 7:31 pm

I tried to see if I could lift the throttle back out when the car didn't decelerate and it doesn't move - it's not sticking..

davekmoore · Postby **davekmoore** » Wed Mar 02, 2016 8:13 pm

If such a Thing existed (and I don't think it does), it would almost sound like some kind of intermittent drivetrain fault.

JBT · Postby **JBT** » Wed Mar 02, 2016 8:16 pm

Pushing the clutch pedal in or putting the car in neutral should put the engine into normal idle mode, which it seems to do OK.

It seems that something is causing the fuel injectors to continue to supply fuel during deceleration with the transmission engaged. Whatever is causing that is probably also affecting the acceleration. My guess is a vacuum leak or some sensor playing up.