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Thread: Slight rough idle & warm starting... VR6

  1. #1
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    Slight rough idle & warm starting... VR6

    Hi,

    I know this topic has been done quite a lot, but I'm just wondering if my two issues could be related.

    When cold the car starts as you'd expect for a 150k motor - couple of turns of the starter and it fires up. Not sure if relevant but the revs got to about 1500 and then drop down to somewhere around 1000. I don't remember my other cars doing this - they usually just co to around a 1000 and drop to 700-800rpms.

    Once some temp is in the engine my idle is around 700 and although the tacho is static you do feel a repetitive vibration whilst it is idling which I consider to be a rough idle. I have seen youtube vids where the tacho is moving and the car is wanting to stall but mine is nothing like that.

    The other issue is warm starting. The starter will crank for a guess 10 times and then the car will slowly splutter into life with no throttle input or if I jab the throttle it will eventually start and rev. Sometimes it won't start and I'll try again and it does start but not as quickly when cold.

    I have no fault codes.

    On a previous car I had a warm starting issue which was the crank or coolant sensor (i forget which but the fault code pointed to it). However on this car with the slightly rough idle I think it's fuel related and possibly a weak fuel pump. How do I test it or is it just a case of they wear out and you replace? And where is the best place/best brand to get a replacement pump? In my head I think the car behaves when cold as the ECU fuelling demand is different on a cold engine but I don't know this for sure.

    I've also seen people are re-routing the fuel plumbing, I think to keep some fuel in the lines but I don't quite understand the job at the moment.

    Cheers,
    Matt
    Last edited by pfnsht; 11th April 2018 at 9:27 AM.
    1995 White VR6 CCGB Member 4303

  2. #2
    CF-oholic! seanl82's Avatar
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    The warm start issue is quite common, and similar on my car with 150k too though it always starts. This has been apparent on cars with much lower mileage as well. Some have changed the temp sensors, the fuel pressure regulator, fuel pump (not sure if its still available anymore to be honest), and also put non return valves on the out line near the pump with varying degrees of success. You could try all of those which will set you back a fair amount of money, or just accept it as a "Corrado nuance" as it may or may not make a difference. WRT the cold start, revs will generally raise to around 1100 rpm initially, but settle within a second or 2 to about 900 rpm whilst cold. After a minute or so the idle should settle between 6-700 rpm which is good.
    There are a few factors which could affect what you think is a rough idle. Not withstanding mechanical faults, but things like worn engine mounts, aftermarket exhaust, slight exhaust leaks or even hoses not secured in clips could all cause resonance at certain levels. Engines have a natural resonance point as you may have witnessed when increasing through the revs, you can feel the car "shake" a little more at a certain point. All those factors could be the cause of a natural point where the vibrations are most apparent. The interior may have also been out at certain points in the cars life, and in most cases the felt lining on trim has come away, or various securing screws etc haven't been put back in which could also be the cause. This is extremely common and rattly interiors are pretty much the norm in Corrados these days!
    95 Classic Green VR - Jetex Cat Back|BMC CDA|VT mounts|Bilstein B12s|288mm front brakes|Mk4 Rears|Braided hoses|BBS RX228s|Daves16v shortshifter|Lupo wipers|Uprated headlight loom|
    http://the-corrado.net/showthread.php?t=79984
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  3. #3
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    Cheers Sean!

    Yes not sure I want to go down the route of changing all of those parts without testing first. At the moment it is starting, eventually. I'll try the cheaper options - Fuel Pump Relay, Regulator first but until it completely fail I don't think I want to be spending on a pump - febi bilstein do one but it's 150 quid.

    Re: the start - just moved the car off the drive to check levels and it does go to 1500, then 1100 and as you say 600-700. Could just be resonation - I don't mind it - i was just thinking maybe a weak pump was consistently pulsating rather than flowing nicely.

    I have changed the PCV as it was torn at the connection and that has made coming on and off throttle less jerky, I'd also thought it might have been causing he pulsating vibration sensation on idle but it's not.
    1995 White VR6 CCGB Member 4303

  4. #4
    CF Nutter fendervg's Avatar
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    For the hot starting - check the residual fuel pressure level at the rail - often a new FPR will fix this. Some have suspected a leak down through the feed hose from the pump and have fitted a small non-return valve there.

    It sounds like you might have a minor misfire there - check/replace your leads and spark plugs and and check dizzy cap and rotor or coil pack.
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    Thanks - is FPR the regulator? They seem cheap enough to try out.

    RE: misfire I hadn't thought of this. I had new spark plugs at the service a few months ago but no idea when the leads were last replaced (if at all). Good shout and easy and easy enough for me to do.

    I've never worked on changing stuff on the fuel system before. Are there any precautions I need to take when changing something like the FPR? I don't want fuel squirting everywhere!
    1995 White VR6 CCGB Member 4303

  6. #6
    CF Nutter fendervg's Avatar
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    Yes, this is the fuel pressure regulator (4 bar) on the RHS of the rail. There is a small allen head nipple on the front left of the rail where the feed and return hoses join up that can be undone carefully with a rag for soakage to relieve fuel pressure in the system.

    Another way is to remove the fuel pump relay and run the engine until it cuts out having used up all the fuel in the system.

    You can use that bleed nipple to attach a pressure gauge to the rail for testing - you should see 3.5 bar at normal running engine on, and this should rise to 4 bar with the vacuum hose to the FPR disconnected. Once the engine is stopped you should still have at least 3.0 bar in the system after 30 minutes.

    Be careful when removing the old regulator from the rail, they tend not to come out easily without being damaged, and it is easy to bend the rail housing if using too much force. If you're replacing it anyway a pair of water pump pliers on the exposed part works well.

    Quote Originally Posted by pfnsht View Post
    Thanks - is FPR the regulator? They seem cheap enough to try out.

    RE: misfire I hadn't thought of this. I had new spark plugs at the service a few months ago but no idea when the leads were last replaced (if at all). Good shout and easy and easy enough for me to do.

    I've never worked on changing stuff on the fuel system before. Are there any precautions I need to take when changing something like the FPR? I don't want fuel squirting everywhere!
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    Perfect thanks for the heads up. I see what you mean on where it is and the water hose clips to remove... working from home is very convenient for nipping out to check these things
    1995 White VR6 CCGB Member 4303

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    ⋆⋆ CF Member ⋆⋆ Jim Bowen's Avatar
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    Am pretty sure mine has always had a slight uneven/vibration at idle, only very slight and is fine as soon as you use the accelerator, i just assume thats how they are.

    Can feel it stopped at traffic lights. If you rev it quickly on/off it does a small pop
    Just like a golf................But better!!!

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    That's exactly like mine Jim - stopped at traffic lights etc. I get a burble when reving say to 1500/1800 rpm once warmed - I love that and standard exhaust too.

    At the moment I am going to first focus on replacing fuel pump relay and then the FPR valve to try and work on the hot start issue. At the same time investigate status of coil and leads as aware heat can make these less effective over time. If I can't fix it after that lot I'll just have to live with it. It is a bit annoying but as the car starts perfectly from cold I'm happy there's not a serious mechanical issue. Oil consumption is minimal and what I have lost is likely to be from the small leak I have on the sump gasket.
    1995 White VR6 CCGB Member 4303

  10. #10
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    RE; the FPR - is this the sort of thing to buy - why is considered an upgrade - isn't the 4bar is standard fitment on the 2.9? http://vi.vipr.ebaydesc.com/ws/eBayI...rsion=890d5c63
    1995 White VR6 CCGB Member 4303

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