I have a 2000 A4 1.8t. Sorry if this is a little long but I want to give you guys the full story instead of saying my car wont start. Anyway this weekend I noticed that my coolant light came on. I could not make it to the dealer so I checked it. It was low not even 1/4 inch from the low line on the reservior. So last night I drive it to the gas station "maybe 5 minutes". First thing that happened was on the way back I went to turn my radio on and it took 5 seconds for it to turn on.Well when I got back home I have my windows down and I heard the sound of a vacume. I thought my wife was cleaning. Well when I turned off the car it continued. I popped the hood and checked to see if the radiator fans were still going . they were not. I put my hand on the plastic 1.8t cover on the engine and I felt air being pulled in through those holes. So it stopped after a few minutes. I took my wifes car to run some errands coming home 2 hours later. When I get home the same sound is happening without the car being on. So I take it for a drive and it runs fine but when I get home I notice that about every 18-20 seconds the idle drops (nothing bad enough to cause the car to stall) but the headlights dim every time it dips. Then to top it off this morning the electronic gauges will not even light up. I have never had a battery this dead. Guys what do you think? Could this have been caused from a faulty battery, alternator, low reservior coolant. Any help would be greatly appreciated. Again sorry if this is long but I wanted to explain the whole series of incidents.

Thanks Again
500tq

 

Sounds like a few probs.
Is the header tank (water bottle presurised when you remove the cap? Blown headgasket? when you take the oil cap off is it a light brown milky colour on the underside? blown headgasket?
have you checked the fuses for dash panel for blown ones? is it def an air pipe you feel not a water one that is bubbling from boiled water?
Are the elements inside the battery dry? this would cause more of a fizzing noise but could explain a few noises. if they are battery will be cooked. dry topping up with de-ionised water and charging up leave for a day or two then check battery for charge holding if flat replace it.

If lights dimming when revs drop as long as they brighten when revs go back up again dont worry it shows the alternator is working properly.

 

blockage in an air pipe will cause air to be dragged through for a short while when switched off as suction will continue for a short time after everything has stopped and when stopped it would back up again. would not think this would be anything to do with it though...

 

Dying batteries can cause freakish things to happen. Get scanned for fault codes and see if there is one refering to voltage threshold. If you dont have an OBDII scanner/multimeter, Auto Zone will do that and check your battery/alternator for free.

I have heard of 1 instance of a blown head gasket on a 1.8t throughout my entire membership on the forums. If your coolant level was really only 1/4 inch bellow the "fill/low" line, then that wouldnt cause your engine to overheat and cause the head to warp/blow out head gasket. The coolant warning light shouldnt have even come on unless the level is REALLY low, or the engine temp is in the red.

Also, there is nothing under the plastic engine cover that can create vaccum through the vent holes. Justa valve cover and 4 coil packs.

Scan ecufor fault codes. Record fault codes (if any). Clear fault codes form ecu. Drive car for a few days/engine cycles. Rescan for fault codes. You might have a fault code stored from a previously fixed problem that never got cleared. Thats why you clear andrescan. Good luck.

 

guys thanks for all the help. By the way one point it was the battery. Well so far. I went and had the battery charged today and tested. Checker told me to come back after one hour of charging. When I came back they told me the battery charged for maybe 5 minutes before the CPU said to change the battery. Anyway I put in the battery and car started up immdiately. I let it run for maybe 10 minutes and no wierd vacume sound. Thank You all. I wrote my fix here in case someone has the same prob. By the way guys I am still 1/4 inch short on coolant in the reservior. Dealer is closed. Where can I but g12 coolant (I think its g something) other than the dealer?

 

Guys I am having the same problem again. One question is there a turbo cooling fan in this motor? Or a sensor for the turbo fan. I drove it today. Its warmer today and after 5 miles I heard the sound under the hood. I popped the hhod and on the left side of the engine right above the turbo and exhaust manifold unit It felt like a compressor was blowing hot air out. I think this is where the problem is occuring. If it was a module or relay it could be causing the fan "or whatever is blowing this hot air out" to turn on even when the car is off, hence killing the battery overnight. Any ideas? Thanks Again Guys.

 

If hot air is blowing around by the turbo, i would replace the exhaust manifold gasket and the turbo outlet gasket too. Those being bad would definitely cause hot air to leak around the turbo. Also, this may be resulting in erratic exhaust gas flow across the turbine, which might explain the fluctuations in engine idle.