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Erratic revs when starting up

Discussion in 'A4/S4 forum(B5 Chassis)' started by Dan Yeates, Nov 24, 2008.

  1. Dan Yeates
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    Dan Yeates Audi S4 B5 Avant

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    Hi,

    My 2.7 S4 has been fine since I bought it, however, recently it's been revving 3 or 4 times, quite high and very quickly, just blips when you start the car up. Haven't had any throttle depressed when starting.

    Also, sometimes the idle is a little lumpy, but it's not that bad, not bad enough to be a problem, it's the strange revs when starting that annoy me.

    Any ideas on what it could be? I'm assuming it's the MAF metre, I found a price on the RS4 MAF metre, but not the S4 one - what's the price on this? I don't want to change the airbox and everything right now, what with xmas coming up etc!

    Also, recently it only seems to average around 18mpg, I used to get around 24mpg ish with similar driving - just running to a from work. It seems to drive ok, but it can hesitate if you put your foot down at low revs, say around 2k.

    Thanks,

    Dan
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  2. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    sounds like it could be a sticking/dodgy throttle body

    Craigs was doing similar oddness and was constantly logging fault codes for it, very occassionally it would blip the throttle liek you describe, othertimes it would just idle high, and occasionally would just stop responding to throttle input at all.

    Have you scanned it for fault codes?

    We changed the PCB on the side of the throttle body with one we baught randomly off ebay from a 1.6 Seat or something, and it seems to have cured it.
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  3. AndyMac
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    AndyMac Moderator Staff Member Moderator

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    Sure it's not the temp sender? That would give all those symptoms and high fuel consumption if the ECu thinks the engine is running cold
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  4. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    true, but would usually show oddness on the guage too?

    Get it on vagcom.
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  5. Lee Goodall
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    Lee Goodall ..got my head together!

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    If it's the throttle plate position causing the problem you'll get a fault code.. could just need a good clean.
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  6. Dan Yeates
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    Dan Yeates Audi S4 B5 Avant

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    Water temp gauge seems normal, oil temp gauge never normally gets that warm unless I'm on a long trip (I live quite close to work).

    I'm based down in the New Forest, not far from Southampton. I'll have to try and find someone with a VAG-COM locally.

    By the way, just took it out this lunch time, just into town about a mile, and it was fine. Started fine, no unusual revs, not hesitation or anything. When I started it first thing this morning it revved a lot when I started it up, it hadn't been run previously for about a week as my girlfriend and I alternate cars each week (we work together). I think it only happens when it's cold.

    Thanks for all your help.

    Dan
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  7. Blue_Thunder
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    Blue_Thunder Active Member

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    If your MPG is shot then it is looking quite likely to be your MAF.

    Your local dealership should be able to offer you an exchange price on your unit for under £90 I think. Alternatively, get in touch with Vagparts (their website is useless) to see what price they come up with.

    Defo get it Vagcom'd to make sure it's that first though!
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  8. Dan Yeates
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    Dan Yeates Audi S4 B5 Avant

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    Right, well I'm going to change the temp sender anyway as it's cheap and it's been recommended I should just change it as a matter of caution. Is ther anyway of telling whether it's the early or late type sender on a 1999 T S4 (facelift), or do I have to go outside and pull it out to check the colour? Also, where is it?!
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  9. Dan Yeates
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    Dan Yeates Audi S4 B5 Avant

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    Ah, another thing after doing some research, if I change the temp sensor, will this affect ym after run pump modification? I understand the modification uses a different Audi sensor, or is this a different sensor altogeher?
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  10. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    different sensor.

    I think if you locate the CTS you should be able to see what color it is without removing it. its the wiring plug thats colored so at most you might have to unplug it.

    Not sure where its located on the S4 though, on the 1.8T it sits in a coolant gallery at the back of the block. Follow the top radiator hose and i suspect you'll find it.
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  11. Dan Yeates
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    Dan Yeates Audi S4 B5 Avant

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    Ok, thanks mate. I've had a look in the S4 self study programme and I think I know where it is from an illustration, I'll have a look at lunch time and get one ordered up. I'm thinking it's done a few miles now so it's probably worth changing this, TBB and hoses, maybe MAF metre and whatever other valves and sensors that may fail. Mission for today is lots of searching to find what I should replace, where they go and where to get them from!
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  12. Blue_Thunder
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    Blue_Thunder Active Member

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    When I got my S4 the first thing I did was get new DV's (710N), a new silicone hose set from eBay and did the afterrun pump mod.

    I'd suggest you also look to do an F-hose delete and an N249 delete. I did the N249 delete myself and it was really easy. The F-hose delete is a little more involved, but will at least get rid of this common failure point. DavidT from AudiSRS.com had his F-hose split whilst on a dyno and his K03's blew.
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  13. Dan Yeates
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    Dan Yeates Audi S4 B5 Avant

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    Thanks.

    I have new 710N's, they're probably a year old tops, and the after run pump mod was fitted by the previous owner.

    I have looked up the F-hose delete but it's hard to understand without the engine in front of me. Will look up the N249 delete, not seen that.
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  14. Blue_Thunder
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    Blue_Thunder Active Member

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  15. Dan Yeates
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    Dan Yeates Audi S4 B5 Avant

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    Thank you.

    I will look at doing that then. Just got my new coolant temperature sender so will fit that tomorrow. I did unplug my MAF metre and coolant temperature sender one by one to run the car to see if it made much of a difference. Without either it ran awful and stalled, however, since I've plugged them each back in, it runs an awful lot better! Seems to start ok now. I'll still change my coolant sender but it seems like it might have just been a dirty connection maybe.

    Had it MOT'd on Friday, 98,000 miles and it passed first time with the only advisory being low tread on the tyre! :) What a great car!!
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  16. Dan Yeates
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    Dan Yeates Audi S4 B5 Avant

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    Changed the coolant temperature sender, seems to have made no difference and it's still spluttering and revving when starting.

    Anyway, I'm going up to York from Southampton next week so I've booked the S4 into MRC for a full healthcheck. Hopefully it's not going to cost me too much, what with Christmas coming up!
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  17. Dan Yeates
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    Dan Yeates Audi S4 B5 Avant

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    Hi again,

    I went up to MRC and had the health check done. Turns out the MAF was gone, which had overheated one of the EGT's. There were also a couple of small boost leaks and a T-piece had broken on the vacuum system. They did the health check and fixed it all in under two hours (the time it took to walk into town and get a good cooked breakfast!) and I'm so pleased by the results.

    They said it was overfueling by 25%, well, on a trip up to York and back it averaged 31mpg and it pulls SOOOO hard compared to before! It's a completely different car and feels so quick.

    I'm so happy with the results, thanks MRC!

    Dan
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