Idle - isv, maf, tps, tb cleaned, readings .. what next!

[pfnsht]

Hi,

Ugghhh, I've read threads and threads on VR6 idle issues and it feels like I've been hunting down this annoying issue ever since i've had the car.

Can't see the tacho move on idle so relatively minor but you feel a vibration pulse through the cabin and when you've got your head in the engine bay you can hear and feel the engine lug and catch itself. It never stalls but it's giving me the sensation it wants to.

I've stripped the throttle body, isv and re secured all vaccum hoses. No fault codes displayed via scanning.

I cleaned the ISV with carb cleaner and lubed with gt40.

On reassembly nothing has changed with the idle issue. When I disconnect the ISV the idle rises slightly and idle is smooth. However that might just be becuase it's not at 640 rpms anymore (it idles between 640-680 on vcds). When being drvien the engine is smooth.

How does the ISV work? is it playing a role once the engine is warmed up? Maybe mine is goosed. It is the orignal unit but wasn't particularly dirty.

All other parts on the throttle body are original and have the yellow paint markers from factory so I'm fairly confident the idle damper hasn't been messed about with.

There are lots of other new parts whilst hunting down this issue and fixing others - coil pack, leads, FPR, fuel pump relay, new PCV, new cam and crank sesnors, new thermostat and sensors.

Haven't touched the fuel pump, knock sensors or MAF. Can't think of much else that would affect it. The car drives fine hence why i've not done the pump or MAF...

Any ideas...

Thanks
Matt

[fendervg]

How bad is it? All VRs idle a bit erratically, even if everything is ok - the late OBD2 VR engines in the Golf etc don't have an ISV and use a motorised throttle body instead, so tend not to have these idle speed issues.

The ISV won't behave any differently when the engine is hot vs cold - it's sole function is to regulate air intake when the throttle is closed at idle by pulsing the valve to allow enough air in to maintain a smooth idle speed. Once the throttle body flap opens again, the ISV won't be doing anything. You could try swapping out with a know good one to see.

Have you performed the basic ECU settings procedure again after all the changes (it's in the Wiki on here). Other things to check would be the injectors and the fuel pressure - I've seen a leaky or old injector causing idling problems.

The most common cause though is still a vacuum leak somewhere, so I would check again, especially the intake boot and the pipework near the air box and underneath there. Even a small, nearly invisible crack can cause issues.

[pfnsht]

Thanks for the reply I haven’t performanced the ecu reset actually. I’ll try this. I normally just let it adapt itself over time, but the battery has been disconnected during the work.

The idle isn’t terrible like you see in some of the videos online. You can’t really hear it in the exhaust note but do hear a subtle clatter in the engine bay as it corrects itself and the vibration in the cabin is similar to the one you get when you don’t give it enough gas when releasing the clutch.

I’ll pay some more attention to the vacuum lines. Is there a DIY technique to follow to fine these leaks? I’ve tried spraying carb cleaner to no avail. Must admit I haven’t given much attention to the lines running to the carbon canister though.

Fuel injectors are a good call. I was suffering from some warm starting issues which could be linked to leaky injectors as well, however since installing a one way valve from the pump outlet it’s been resolved. I don’t think it would hurt investing in a fuel pressure gauge as well.

[robrado974]

Let us know how you get on . I’m still finishing the interior as and when I get the time. I have left my dodgy idle for now . I will be checking the hoses again in due course and the oil breather valve which I haven’t checked. Really annoying issue .

[Keyo]

After changing the MAS, PCV Valve and hose, FPR , Cam Sensor , ECU and fuel pump relay and Crank sensor my car is starting great and running smooth, it had new leads and sparks last year alongside battery also getting a new starter next week as making an awful squeak sound on start up. However taliking about the ECU my car had a remap in 2003 in conjuction with a BCA air filter and Shrick VGI, not sure wether I need to got to Stealth and have it remapped as I have now fittd a Stock air box which does not suck in as much air also how much they would charge.

Reckon an older car would benefit hugley from the injections having a professional clean. Have you had any error codes to do with mixture ?

[pfnsht]

No error codes currently, but then OBD1 isn’t that great for error reporting.

Before I delve into taking out the injectors (had a quote @ £85 from Mr Injector) I’m going to try:

1. Clean the MAF and TPS sensors (I didn’t do this when I cleaned the TB and ISV) with electrical contact cleaner.
2. Vacuum leak check again, especially under the airbox
3. Multimeter 5v testing of the sensor plugs
4. the ECU reset
5. See if I can run a TB recalibration via VCDS although believe what I have read is for OBDII cars.
6. Fuel pressure test at the rail
7. Injectors
8. Chalk it up to experience and pay a professional…. But I am enjoying the troubleshooting at the moment.

The issue does smooth itself out and gets worse occasionally. Makes me think it’s a sensor dying. Equally vacuum leak is high on the cards as the problem is only at warmed up idle (and not during the higher cold start idle).

[Keyo]

MAS sensors are not cheap and Im a sucker for BOSCH parts if possible but I just went for JP Group, and by all accounts looks well made very happy with it its Danish and cost £65.

Im changing the cat and exhaust soon and have a new Bosch lambada sensor , I reckon this will really finish off the smoothness of the engine.

One thing many people over look is the recirculation system in late VR6 which incorporates a breather tube from the petrol fill cap area then onto the carbon canister which releases gasses to a light blue solenoid (connected to ECU has a socket and plug)located by the by the airbox , if the solennoid jams open this can also lead to some of your symptons. Also the PCV vavle, so many possibilties, but the way I see it are most of the parts are very old on the car so any part replacemnt for the car is a huge benefit and not fitted in vain.

Be interested to hear what you discover after your investigation.

https://www.ebay.co.uk/itm/New-JP-GR...72.m2749.l2649

[pfnsht]

Thanks for the link! Yes I normally prefer known brand parts but where I’m replacing like this on whim I’m prepared to take a punt. The Bosch MAF’s are too much for me @ ~£200 so the one in the link is more a normal price for MAF imo.

[Keyo]

Thanks for the link! Yes I normally prefer known brand parts but where I’m replacing like this on whim I’m prepared to take a punt. The Bosch MAF’s are too much for me @ ~£200 so the one in the link is more a normal price for MAF imo.

I did mate I still have the old Bosch one in the garage , it is an absolute rip off the Bosch one for a rado my merc Bosch was only about £105 nippers new. Hope you sus out the issue but in doing so you are really performing a good health service to your motor and reliability.

[fendervg]

After changing the MAS, PCV Valve and hose, FPR , Cam Sensor , ECU and fuel pump relay and Crank sensor my car is starting great and running smooth, it had new leads and sparks last year alongside battery also getting a new starter next week as making an awful squeak sound on start up. However taliking about the ECU my car had a remap in 2003 in conjuction with a BCA air filter and Shrick VGI, not sure wether I need to got to Stealth and have it remapped as I have now fittd a Stock air box which does not suck in as much air also how much they would charge.

Reckon an older car would benefit hugley from the injections having a professional clean. Have you had any error codes to do with mixture ?

I'd say the remap was purely to allow for the Schrick VGI and to do some fettling of the factory code in the ECU. Unless you have a turbo/super charger pushing more air in, the engine will be sucking in exactly the same amount of air with the stock air box as it would with a cone. The only real difference is induction noise on a naturally aspirated engine, so assuming you still have the VGI on, you should be fine.