Audi A4 (1995 - 2000) - 1997 1.8 Fuel Management Problem. I Think! | Technical matters | Back Room Forum

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Sat 7 Mar 2009 16:08

1997 1.8 Fuel Management Problem. I Think! - Diff Buster

I have a 1.8 Audi A4 5v and It has about 143000 miles on it. It won't idle properly. The revs fluctuate and they drop to around 500 rpm and bounce back up to about 1500 rpm. It eventually got worse and the car wouldn't idle at all and while revving the engine at mid range and holding it, it would cut out and then go back up again. I changed the fuel filter 2 months ago which helped a bit for a while but the problem has came back full force. There's also a loud hissing noise from the petrol cap which i'm unsure about. I was thinking it may be a clogged fuel pick up or the pump has seen better days. It has me baffled. Any help or advice would be greatly appreciated. Thanx.

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Sat 7 Mar 2009 18:05

1997 1.8 Fuel Management Problem. I Think! - Peter D

Does it run OK when first started. Is the hissing air being pulled in or coming out, I suspect in, this may indicate the fuel tank breather is faulty/blocked. Does it recover if you remove the petrol cap. Regards Peter

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Sat 7 Mar 2009 18:13

1997 1.8 Fuel Management Problem. I Think! - injection doc

You need to check the breather pipe around the throttle body, its sounds like you ,may have an air leak. The throttle body may need a thorough clean & a basic idle reset carried out with a diagnsotic tool.
Throttle bodies do suffer with faults and make your eyes water when you have to buy.

If there is continual suction from the tank you may have an EVAP valve stuck open wich draws fumes from the fue;l tank to the inlet manifold to burn of fuel vapour. The fumes come via a charcol canister.
Is the hiss just a swift one when you open the cap? If there was too much suction on the tank the tank would collapse.

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Sat 7 Mar 2009 20:17

1997 1.8 Fuel Management Problem. I Think! - Diff Buster

The hissing noise is coming from the top of the filler cap area. If i remove the cap it still makes hissing sound. It seems as if some sort of air pump is pressurizing the fuel tank. It's definately not creating vaccum. The breather pipes were joined with cable ties which aren't up to much and on inspection of the breather pipe one of the rubber O rings was not seated properly in it's reccess so there was more than likely an air leak between the throttle body and air flow meter. this also tells me that someone has been working at these parts and neglected to re-fit them properly so i had to go and get 70mm jubilee clips to replace the cable ties. The throttle body has evidently been worked with so i will have to get it out and clean it up and inspect it. How much should i expect to pay for a re-set and/or a replacement part. The car didn't cost me much and i've had my moneys worth out of it already. I want to sell it on but i won't sell it the way it is. It can be quite dangerous when it cuts out while approaching junctions etc.. Many thanks.

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Sat 7 Mar 2009 21:35

1997 1.8 Fuel Management Problem. I Think! - dieselbob

My old 1.6 A4 had both your syptoms. The hissing from the tank is, as suggested above the EVAP valve. I simply blocked of the pipe going to the tank with a clip, if you disconnect it dirty air can be drawn into the engine through the faulty valve. I never solved my idle problem but i would now suspect a faulty/dirty MAF sensor on the air intake as my own problem started soon after i fitted one of those oil soaked air filters, older and wiser now!

Edited by dieselbob on 07/03/2009 at 21:36

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