Slight rough idle & warm starting... VR6

[_Matt_ 26]

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

Edited April 11, 2018 by pfnsht

[seanl82 23]

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!

[_Matt_ 26]

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.

[fendervg 30]

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.

[_Matt_ 26]

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!

[fendervg 30]

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.

 

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!

[_Matt_ 26]

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 :)

[Jim Bowen 1]

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

[_Matt_ 26]

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.

[_Matt_ 26]

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/eBayISAPI.dll?ViewItemDescV4&item=380193167390&t=1314194734000&tid=310&category=61258&seller=su_nioj&excSoj=1&excTrk=1&lsite=3&ittenable=false&domain=ebay.co.uk&descgauge=1&cspheader=1&oneClk=1&secureDesc=0&oversion=890d5c63

[dr_mat 0]

In my experience, any multi point fuel injected car that can't fire up cleanly inside a couple of cranks has a problem, so you do need to get to the bottom of the warm start issue. The rest, I would say, sounds pretty normal though..

 

Regarding rough idle.. most of these cars are lightly used. I would guarantee that if you do 20 miles a day at steady motorway speeds that rough idle will disappear in a week... and come back again after a few days of short journeys.. just how it is on old engines. You'd be looking at valve stem seal repairs and the like to resolve this permanently I would think.

 

Regarding cold start revs. I would say this varies with the extremes of winter temperatures. It's been pretty cold of late... bear that in mind in what you consider is normal.

 

 

A Corrado is for life, not just for the MOT.

[fendervg 30]

2.8 VR6 engines found on the Golf 3 and others use a 3.5 bar regulator, the 2.9 VR6 ABV needs a 4 bar.

 

I wouldn't believe any of the other stuff in the description - makes no sense. All the FPR does is maintain a constant pressure in the fuel rail, everything else is done by the ECU and the injectors.

 

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/eBayISAPI.dll?ViewItemDescV4&item=380193167390&t=1314194734000&tid=310&category=61258&seller=su_nioj&excSoj=1&excTrk=1&lsite=3&ittenable=false&domain=ebay.co.uk&descgauge=1&cspheader=1&oneClk=1&secureDesc=0&oversion=890d5c63

[_Matt_ 26]

I see your point mat! I do use mine quite a lot at the moment, for an old girl - 100 to 200 miles at the weekend (fast roads) and around 50 miles in the week.

 

The warm start is pretty constant - today started up from cold on 2 or 3 starter turns. 8 miles to Sainsbury's along B roads and restart was about 10 turns. Off to nursery (less than a mile) and around 15m mins fannying about picking the kids up and again 10 cranks to start.

 

And thanks fendervg - that clears that up for me.

[_Matt_ 26]

Update - whilst I await my diagnostic reader to arrive I decided to in plug the air flow sensor and the car started straight away when warm. Plugged it back in and same symptoms - difficult to start. Might have struck lucky.

 

Next question my part number is 021 906 462 - but a Bosch replacement sensor is the best part of 200 quid. Last time I replaced one of these I paid about 60 so has anybody else managed to find one for a more reasonable price? I’m assuming Bosch is the right make to go for and is what is currently on the car.

 

Cheers,

Matt

[dr_mat 0]

Update - whilst I await my diagnostic reader to arrive I decided to in plug the air flow sensor and the car started straight away when warm. Plugged it back in and same symptoms - difficult to start. Might have struck lucky.

 

Bear in mind that if you unplug the MAF the car goes into "default" fuelling mode and the car will run differently .. the MAF may not be the fault. Get a used one to compare...

 

 

A Corrado is for life, not just for the MOT.

[_Matt_ 26]

ahhh didn't realise but should have figured everything is all connected somehow. Would I be right in thinking my fuelling - i.e. pump and pressure in the system is good if default fuelling starts the engine with 1 or 2 cranks (vs 10+ when it is connected)?

 

I have a multimeter but haven't had to learn how to use it. Now seems to be a good time to start testing sensors? Also what's the Blue sensor under the MAF? I noted the black, blue, yellow from the termostat and was thinking the one under the MAF was an air temperature sensor?

[_Matt_ 26]

Resurrect my old thread. This issue was resolved when that car went to Stealth for chains and a topend rebuild. It also had refreshed injectors and a new fuel pump. 

Ironically my current Corrado, just back from stealth with a top end rebuild now has the warm start issue, but not as bad as my old one, say 6-8 turns of the starter. My gut feel is leaky injectors dripping a small amount of fuel into the cylinder and there being more fuel than the car expects. On my last one I changed everything prior to injectors/pump. My pump on this one appears strong on the rolling road. 

[Dox 22]

Observe the RPMs on the dash when long crank appears - crank sensor if the needle doesn't move.

VCDS, check coolant temp and ambient (if possible on OBD1?) - there's a CTS temp / resistance value table in the Bentley manual

Coils fail mostly when hot - problem being crank and cam sensors are a coil, as is the coil pack if its a miss-fire.

Does the aux coolant pump run?

[_Matt_ 26]

Cheers Dox. I hadn't noted the RPMs will check that out.

RE Coolant - i have a new blue sensor in there as there was a fault (reading wierd temp) on vcds but this was ealier this year.

The aux coolant pump does run on ignition.

Coil - hadn't thought, i have spares and 1 new unit. Will try to rule it out, although the car is running smoothly otherwise. 

[fendervg 30]

Injector leak-down is a good shout, also worth checking residual fuel pressure is not dropping too quickly. Some on here had some success resolving long crank times using a non-return valve on the fuel pump feed, but there are so many variables and components that could be old and faulty in the loop that it can take a bit of time to track down.

[Cressa 44]

Matt, I changed the fuel pump on mine but also added a 1 way valve just after it, as others have done as Fendervg says. That sorted my warm start issue. I dont know if it was the pump or the valve but it worked. For a tenner it was an easy one.

https://www.ebay.co.uk/itm/131628033416?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=UTSXzBEVT-m&sssrc=4429486&ssuid=SuQ1hX6ZSQa&var=&widget_ver=artemis&media=COPY

A sytec motorsport one off Ebay, 8mm. £15 !! Now. With a foot of pipe and 3 jubilee clips you dont need to cut the original pipe and it is reversible if you dont like it 

I'm jealous as I need the top end doing on my car 😇

Good luck anyway

[_Matt_ 26]

Cheers, I've swapped out the ignition coil but yet to find anytime to use the car. Also have a new bosch crank sensor to fit that i've had on the shelf for a long time, may as well fit it.

I did the one way valve on my last car with no success but it was either the pump or the injectors that solved it last time. Could be different with this car of course, my white one really struggled and spluttered to life where as this just cranks for longer than you'd expect and then fires up normally at the point you'd naturally give up (fine when cold, and fine on immediate restart when warm - happens when left for a few minutes or so i.e. getting fuel). 

 

 

[Dox 22]

Also notice if the brake pedal drops when started - servo vac leak - FPR uses vacuum hence why you start the car throttle closed for max vacuum