Poor idle and running when cold

[MikLSP 0]

Hi, I'm embarking on sorting the problems with my first Corrado now and one of these is a very poor idle and rough running when starting from cold.

 

The car starts no problem but the revs are not smooth and it will just constantly stall. As it warms up this gets gradually better and once the engine is up to temperature it runs very smooth and has a nice steady idle.

 

Is this likely to be a temperature sensor fault and if so which is the most likely suspect/how should I diagnose.

The engine does also have Schrick 268 cams which may be a contributing factor but as I mentioned it does idle just fine when warmed up.

 

Thanks,

 

Mik

[Supercharged 2]

May well be a cooant temp sensor fault but a diagnostic check should be the first port of call

[MikLSP 0]

I don't have VAG-COM access but know a man who does when I can get there. It;s going in for a check tomorrow for a few things so hopefully they'll find the fault.

 

I take it the engine should still be able to run ok when cold on 268 cams?

 

Mik

[pummer67 0]

i recently had similar symptoms and mine was the blue temp sensor. I put 1 resistor in the plug on startup and then a different one for when engine warmed up. I got the new sensor for less than 5quid from gfs. I think any of the other sensors can give similar symptoms though. Mine took a while to diagnose as it was intermittent to start with and then eventually really struggled starting it. Oh yea i the resistors i got from maplins for a few pence. Mark

[MikLSP 0]

Thanks for the reply, I've seen the "blue temperature sensor" mentioned before so this is perhaps a common culprit.

I think I should have no problem with VAG-COM diagnosing it as the problem is not intermittent, if the engine is cold it's rough.

[Kevin Bacon 5]

Yep, if it's rough when started and better when warm it's a sure sign of insufficient warm up fuelling. The VR6 definitely loves a drink when it's cold.

 

The ECU loads a default value of 70 deg C if the BTS fails (so that it doesn't over fuel when hot and destroy the cat), meaning you effectively have no warm up fuel at all.

 

The crank fuelling will always start the engine no matter what as it's preset, but what it does when running is then up to the various sensors.

 

If not the BTS, the next 2 favourite culprits are a the idle valve and MAF sensor.

 

The idle valve turns in two directions (most others are a one way plunger against a spring) which often seizes in one direction, meaning you either get an idle that is too fast, or more commonly, a very slow or non existent idle, which also stalls easily when pulling up to junctions. A clean and lube generally helps that.

 

Dead MAF - ECU doesn't know how much air is being drawn in and guesses based on throttle position. It does a half decent job and many people don't realise it's doing it, they just notice a slight lack of power. That also causes stalling when hot.

[MikLSP 0]

Thanks Kev, a very informative reply (as usual) :cheers:

 

I will see if the diagnostic shows me tomorrow and if nothing I'll start with replacing the sensor. I am of course assuming that BTS stands for Blue Temperature Sensor?

[lycara 0]

I am also having similar problems but not sure what it is. It struggles to start up first time but does start after a few try s but it runs very rough and even when warm. It is like it is almost over running and very jerky when cold and hot. :confused4:

[pummer67 0]

yea bts stands for blue temp sensor. Have you found problem yet?

[MikLSP 0]

Replaced the blue temperature sensor today but it unfortunately didn't fix the poor cold idle.

From there I decided to take off and clean up the air intake, throttle body and ISV.

 

Got the throttle body nice and clean, there was a fair bit of dirt gathering around the butterfly.

 

The ISV was very dirty and was open a little, I'm not sure if this is it's correct position or if it should close fully?

I was also unsure whether it's possible to dismantle for proper cleaning so just gave it a blast with fluid. Can it be opened up or is carb cleaner the way to go?

 

My cold idle is now definitely improved but still not right, I think the ISV needs a better clean out.

 

I also noticed a split in the hose going into the breather valve which is no doubt contributing.

[fla 9]

yes it remain slightly opened. Dont be tempted to put a screwdriver in there to open it as it moves the other way. Just give it a shake up with carb cleaner and lightly lube the flap. Might be worth testing it by pulsing it with 12V to see the flap moves smoothly and doesnt stick.

[MikLSP 0]

Thanks, I'd never seen in one before so had no idea if it was stuck in that position. I briefly considered trying to remove the electrical connector as there seems to be a separate plastic end plate and I thought it might be a route in but quickly decided not to as I expected to end up with something broken if I tried without looking it up :lol:

 

I will give it another blast with carb cleaner.

When you say pulse with 12V, can I connect it directly to the battery or should it be through something a little more controlled?

[mlyon89 0]

Im also having the exact same problem. I also replaced the blue temp sensor with no improvement to the cold running! :(

I might try what you have done and give the ISV a clean out and see if it makes a difference. With regards to what you were saying Kev could it possibly be both and,or just the throttle position sensor and MAF, if you say that once the MAF stops working the ecu relies on the TPS to guess??

[MikLSP 0]

Certainly give the ISV a clean and the throttle body too, mine now only struggles for about a minute or so and then settles down rather than until the coolant got up to temperature as before. I'm going to give the ISV a better clean out and sort that breather hose and hopefully then it will be fully resolved.

[dalhalvaig 0]

I've been noticing for that last few weeks that the car starts OK, but as I drive down the street, that there can be a bit of a hesitation as I apply the throttle. Once the car warms up this seems to disappear. However on Wednesday i drove the car about 45 miles cross country in the rain - motorway and A and B roads. No problem. After 3 hours did return trip - more rain - no problem. Pulled in and stopped for about 15 minutes. When I restarted the engine started OK but when i touched the accel pedal, the engine almost died. tried a few times and basically the car would not keep the revs up high enough to move. After coaxing it for a few minutes it seemed to clear and managed to do another 15 to 20 miles no problem. Today, drove about 5 or 6 miles in town - stop start, engine warm enough for fans to be kicking in. Parked for about 25 mins, and while the car pulled away OK it was almost like it was in limp home as it wouldn't above about 2500rpm (can't remember exactly). After about 5 minutes driving it cleared, but I kept having to work the gears to keep it moving.

 

Is this a similar problem?

 

VR6 - no mods, except immobiliser

 

D

[eugopnosaj 0]

Mine has developed this issue this morning, doesnt start very well and has a rough idle till ive driven it for a few miles. She also stalled after about 100 yards...

[VW_OwneR_85 1]

does it idle up and down? and rev realy low to the point of almost cutting out?

[eugopnosaj 0]

does it idle up and down? and rev realy low to the point of almost cutting out?

 

yeah pretty much, lights were flickering and i had to give it a bit of throttle to stop it stalling

[markieshero 0]

My 16valver is doing the same recently, as long as it heats up it goes like a dream, but on cold start chugs and loses power. Where exactly is the BTS(blue temperature sensor) located, on the inlet manifold? I noticed that the coolant gauge doesnt seem to be going past 70 degrees as mentioned in this post so Im guessing this maybe related somehow, possibly the default has been adopted by the ECU?

 

Any joy with this issue guys?

 

 

MARK