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italianaudi318
12-12-2009, 06:39 PM
my car is a 1999 Audi A4 1.8T. When im driving and I go to take my foot off the accelerator sort of fast to put my brake on, the engine will "shake" back down to idling speed. I was just wondering if this was normal? or if there is anything I could do about it.
-if you need more information to answer this, PLEASE ask [:)]
Thanks

walky_talky20
12-12-2009, 07:26 PM
Maybe just some pulsation in the brakes? Hard to say. I'm guessing it is Automatic?

If you select Neutral at highway speed and then hit the brakes the same way, does it still do it?

lotusgardener
12-12-2009, 08:55 PM
Could be your snub or engine mounts.

italianaudi318
12-13-2009, 05:42 PM
no its not the brakes, yes its auto. I come to a complete stop, then after you feel the back end of the car sit down then the engine sounds like it goes under, almost like its about to stall? it is wierd hahaa

walky_talky20
12-13-2009, 07:17 PM
Could be a vacuum leak. I had a big vacuum leak due to a broken PCV system and my idle was very jumpy, especially stopped when in gear (tiptronic). Do you have a boost/vacuum gauge?

italianaudi318
12-14-2009, 03:54 AM
no i do not :(

Seerlah
12-14-2009, 05:02 AM
I think he has a huge vacuum leak.

To the OP, if you don't have a boost gauge you should def invest in one. These cars should have come stock with one. Either way, you can determine if you have a leak or not by doing a boost leak test. Just be sure that you have a gauge control how much pressure you place into your system. If you hear any leaks, then fix them. And if you have a gauge on the tank which you are pumping air into your system, if it drops at a steady rate then you def have a leak.

italianaudi318
12-14-2009, 12:24 PM
i dont know much about cars so i dont know the answer to this question; will a vacuum leak cause significant damage if untreated?

jpcallmotor
12-14-2009, 08:53 PM
^^^ Yes, a major vac. leak can do damage. Your car will run lean, which means more air to fuel ratio. In turn combustion temps. will be much hotter and you run the risk of possibly burnt valves, or can even blowing a hole in a piston. Thats on the way extreme side, and is unlikely given your conditions...

italianaudi318
12-15-2009, 11:59 AM
oh my, thank you for telling me that

RockyMountainB5
12-15-2009, 03:24 PM
I'm with everyone else, you have a vacuum leak.
On the good side, its prolly gonna be cheap to fix.
On the bad side, its prolly gonna be really hard to find.
It could be any of the various PCV & crankcase breather hoses, vaccuum hoses, ect.