Surging at Idle

[craig_the_german]

Hi all,

I guess this is an age old issue with the Golf 4s with the 1.6L AKL engine but I am hoping someone may have a new slant on the problem.

The issue is with the engine at idle. The car can be idling along just fine and then for maybe a minute the idle surges up and down a few times between about 400rpm and 1000rpm. It does this smoothly and never cuts out. After a minute of this, the idle settles without having done anything to make it do so.

I have checked for vacuum leaks and I don't think there are any (could be wrong..who knows ) The car revs smoothly and drives well and doesn't seem to have any other "misfires" etc.

You would think that if there was a vacuum leak it would be there all the time (again..might be wrong)

I guess the next thing to look at is a TB clean???, maybe check the fuel filter???

If anyone has been successful or has similar symptoms, I am open to all suggestions.

Thanks

Pete

[Manaz]

Turn off the A/C and see if it still does it.

[craig_the_german]

A/C is off.

[gavs]

Craig, I have been chasing exactly the same issue. About 2-3 months ago, it was really, REALLY bad. Sometimes it would even stall the car. First thing I did was a timing belt and serpantine belt, along with a full service, this actually helped considerably because after leaving the battery disconnected for 2 hours or so, it cleared any fault codes in the ecu, the normal one being a supopsedly faulty lambda probe (incidently, after doing the timing belt, this code has not been thrown since!).

Next was a though check for vacuum leaks, which turned up nothing, annoying because the AKL is notorious for air leaks. So then I checked the coolant temp sensor and lo-and-behold, the old style, faulty black one. While waiting for my new green sensor to arrive from ECS, I also changed the spark plugs on sunday (incedently, the plugs looked brilliant, the inside of my engine must be working just nicely!), the odd cough is still there, but not glaringly obvious, so I plugged in a VCDS to do some live data tracing, turns out that the car is running slightly rich at idle, not so much under load, but still on the rich side, apparently a common indicator that the temp sensor is misbehaving.

The other thing that VCDS did is to help confirm the sensor is a bit dodgy, sitting in a traffic jam last night saw the VCDS screen show a temp of close to 100 degrees C, whereas the guage on the dash still showed just on 90. now, I don't know which one to believe, but for 10 bucks (plus another 40 in shipping!), a replaced sensor seems like a good investment. And when I sell the car in the next couple of months, whoever buys it is going to get a ripping car with every little thing that could be done to sort out the engine done to it

Now to find a buyer....

[craig_the_german]

Hi, thanks for the detailed reply..it all helps.

I have just replaced the serpentine belt, timing belt and water pump was done 40,000km ago so not all that old. I have checked for vacuum leaks as best I can and don't seem to have any.
I have the green temp sensor (after the old black one failed).
Spark plugs are not that old either.
I plan to give the MAF meter a clean as well as the throttle body incase at idle there is just enough contamination to effect the running.

Apart from that, I will continue pulling what little hair I have left, out

[gavs]

Maybe look at a throttle body reset, if it was done at the wrong altitude, like on a mountain, it might not be operating how it should....

[craig_the_german]

Hi, Is that something I can do myself? I don't have vagcom etc.

I (might be mistakenly) thought that a throttle body reset applied to those with "drive by wire". Mine has the old cable style.

[gavs]

It is a VAGCOM thing you will need to do. I don't know exactly how it works but I believe (willing to be flamed here by someone with more knowledge) that it has something to due with calculating the open angle of the butterfly and has something to do with the amount of fuel going into the engine in conjunction with the other sensors....

[craig_the_german]

Hi again,

Here is the bit I don't understand....drove to and from work today (30km each way), to and from the shopping centre tonight and it never missed a beat, no surging, misfires, stuttering...and I did nothing......

Tomorrow maybe a different story.....how would you know

[Jmac]

Just remember there is experience not that far away all you have to do is ask:/
Internet diagnosis or google mechanics dont fix cars, its all could be this could be that, hence my reason for posting a lot less,
Hope you get to the bottom of it mate, seen a few things lately making me feel the way i do, not aimed at you in any way
Cheers
Jmac

[craig_the_german]

Thanks Jimmy, I know that you are only a phone call away. I just want to try and eliminate all of the obvious things before I call in the experts

I am trying to avoid a "dooh" moment. hehe

Pete

[gavs]

Just remember there is experience not that far away all you have to do is ask:/
Internet diagnosis or google mechanics dont fix cars, its all could be this could be that, hence my reason for posting a lot less,
Hope you get to the bottom of it mate, seen a few things lately making me feel the way i do, not aimed at you in any way
Cheers
Jmac

Good point.

PS, it was that damn coolant sensor, sorted my issue out now