VW Golf 3 1.6CL Starting and (uncommen) idle problems

[C_Cheetos]

Car details below wall of text.

So I have this strange problem with my golf 3, it wont start unless I help it by placing my foot on the accelerator. If I don't the engine will start-up right away BUT once I release the key from the starting position, it will cut out. If I run the starter for about 15 seconds, the engine sometimes wont cut out. I have noticed, that unlike other golf's and polo's the revs react pretty slow to starting.

Normally once the starter turns on the engine, the revs respond (instant) by climbing to around 1800 rpm (correct me if I'm wrong) and then drop down to around 11-1200 rpm while coolant is below a certain temperature (40-50 Celsius). My car starts responding after about 10-15 seconds if I keep the starter running. The work around for this is for me now, is using the accelerator, while starting.

problem 2: which is probably somewhat related to the first problem? My stationary idle is different from my moving idle. (This makes traffic jams more of a pain then they already are...) What I mean with this, is that at a full stop, it idles smoothly at 600 rpm, once I start moving (at 3±1 km/h, yes I have tested it.. don't ask) the revs shoot up to around 1100 rpm then drop down to 950 and stay there. This happens in neutral, in gear with the clutch panel pressed, and while slowly driving away only using the clutch.

When I am already moving and I press the clutch, the revs will slowly go down to 950 rpm, until I hit that magic 3 km/h and they will drop down to 600 rpm...

I am not a car mechanic, I'm a physicist, but I have some experience in working on cars and I own VCDS-lite. My first guess was throttle body related issues, I tested it, the thing was far from perfect, so I replaced it with a brand new one and performed basic settings (this fixed a common problem, that the rev needle would keep wobbling AKA hunting for gas).

The curious thing is, once I perform basic settings, the idle problem goes away completely for a few days(starting problems persist though). This means, that whatever speed I'm driving my car, it always idles nicely at 600 rpm. A couple of days later I start it, and I can already tell by how it behaves while starting that my idle problems have returned... so I drive it, till the coolant reaches about 40-50 degrees Celsius (since below that temperature the idle is always higher than 950) and of course the difference in stationary idle and moving idle has returned....

replaced: throttle body (and o-ring), spark plugs, spark plug leads, rotor and distribution cap (yes I've put the leads back in the correct order), thermostat, thermostat housing and sensor, coolant, oil, oil pressure sensor, catalytic converter (at a licensed garage), water pump and timing belt (also in a garage, didn't have time to do it myself).

Also removed rust from all negative leads and contacts I could find, reattached them and repainted.

 

Make: VW Golf mk3

Model: 1.6 CL

Year: 1996

Engine: AEE

Engine Code: AEE 090 993

ECU: Marelli 1AV 1949

Mileage: 262xxx Km

 

Sorry for the wall of text, I have pretty bad ADHD so I hope my story makes some sense, I hope someone has a clue and can help me, because I'm at loss here.

(I hope I covered everything, since this is the 2de time I had to type all of this, because the website gave me an error while posting)

 

[Cuprabob]

Is the fuel pump priming? On VWs the fuel pump primes when you open the driver's door. Leave a 20s or so delay between switching on tbe ignition and starting the car to allow the pump to prime if it's not when opening the door.

It's common for the switch that detects the driver's door opening to fail meaning the pump doesn't prime. Other symptoms are interior lights don't work when you open the driver's door and the lights on buzzer doesn't work.

On the last few VWs I've owned including my current Scirocco, the idle is higher when rolling and only drops when the car stops. 

[C_Cheetos]

wow, I never knew this, pretty nifty feature, sadly/luckily.. my interior light switches on the instant I open my door, buzzer works every time.

I never knew that some cars had higher idle when rolling, doesn't explain why it happens after a couple of days since basic settings though..(sometimes the same day, if I remember correctly problem always starts after a fresh start, wont go away after that).

Thanks for the quick reply

also, important detail perhaps, if my idle problems start, it wont idle at 600 any more, it goes up to 640 at full stop. Almost as if the throttle body settings changed for some reason.

The other day I was driving, and suddenly the radio cut out, as in no power at all, but started right up after deattaching the front panel and reattaching it, probably not related, but could indicate that something might be wrong with my constant power supply line? or perhaps a spike from the negative? Gonna check my coil for cracks in a minute..

 

Edited November 19, 2016 by C_Cheetos
Grammar + additional info

[Cuprabob]

Another common issue on VW engines is the engine coolant temp sensor. When it fails it gives wrong readings to the ECU making the car difficult to start and run erratically as the fueling is wrong due to the faulty sensor. Worth a look and a cheap and easy part to replace 

[C_Cheetos]

Did a quick test run on the temperature sensor as you suggested, before starting the ECU gave a temperature of 15 Celsius, and my thermocouple sensor (the volt meter you see) gave a reading of around 20 Celsius. But my thermocouple was placed in the reserve tank for the coolant, so this could be the difference.

after starting the temperature climbed up nicely as it should, don't have a picture of 90 Celsius, but it got there in a couple of minutes. Don't mind my sensor (in the dashboard picture) as it turns out, it was pushing against a side of the plastic reservoir, which is obviously much colder than the coolant.

once it got to 90 Celsius, I got out and did a proper measurement with my own sensor, I've included the picture for this one as well, ECU reads 90, my sensor gave 76-77. didn't do the maths yet. But I guess the reservoir is cooler? (will probably have to do another test with my sensor placed somewhere in a radiator hose...)

A stupid thing I did notice, besides that the coolant rises if I leave the cap off... is that I had contaminated my sensor with something pls dont be oil.. it was oil.. from my coolant reservoir.

So now another question arises, could the starting problem be related to a blown head gasket? or might there be another way for the oil to find its way to my coolant?

oil cap wasn't milky btw..

 

[Cuprabob]

I'm not too familiar with that particular engine and whether it has an oil cooler at the oil filter which has a coolant jacket. With age they rot and oil gets into the coolant. Otherwise it looks like a head gasket, which is very common in VWs of that era.

A blown head gasket could also cause your running issues as compression will be lost in one or more cylinders. 

[C_Cheetos]

This would explain the struggle it has while starting right, since it kinda needs the right compression.. I don't have any means to test compression here, I do however have an endoscope, can I simply look down the spark plug holes and identify a head gasket leak from there?

-----THE NEXT IS AN ASSUMPTION! (for future reference should someone in the future google these symptoms) being an experimental physicist I have some basic knowledge of chemistry. Since it is a gasoline engine and they are far from perfect, would it be safe to assume that carbon deposits have build up on the cylinder heads? carbon deposits are mainly only the element carbon (C) and coolant also having water (H2O), which would normally not react, but when heated (even more so when under pressure and heated) will make the following reaction: C + H20 = CO + H2

This could mean 2 things, but I could be wrong here.. in essence my cylinder heads would be cleaned due too the coolant leaking in there? (probably not the best assumption, since a lot more complex stuff goes on in there). But this could also mean that there would be a detectable change in exhaust fumes? (and why it didn't pass emission tests, where after the garage, were it was tested, told me my catalytic converter was bad). I just realised Hydrogen gas is highly flammable, so that wouldn't be detected.. but an increase in CO could be measured probably. I have equipment here to try that but I don't really have anything to compare it too..... any ideas? (I'm making this way to complex I think) ------

 

Alright, how can I check if there is an oil cooler, I know that I have a single screw on oil filter.

I have heard that loose head bolts could potentially also cause this? I will check the torque on those first... but doubt it

I have tried as best as I can to take photographs of where I believe an oil cooler would be, if there is one. I could be wrong though.

 

[Cuprabob]

Certainly no oil cooler there. It probably doesn't have one with it not being a performance orientated engine. 

I doubt you would be able to see a blown gasket by looking down the plug holes with an endoscope unless it was really bad.

As an experimental physicist, I expect you write a lot of papers. Based on your posts I bet you struggle to.keep the word count down:-) 

[C_Cheetos]

Haha, thanks for your help

scrolling up, I see what you mean, matter of habit I guess