VW Golf Mk2 Owners Club

Rough cold starts

August 11, 2025, 07:16:33 PM

Hey,

Got a digifant 8v. Car was fine but in the past couple months has started to struggle to start. Often it starts and it's super rough, sounding almost like it's cammed, sometimes it's even so lumpy that it cuts out. Once it cuts, it really struggles to start again. Once it is running and has had a few moments for the revs to settle, it runs perfectly fine, and once it's hot will start again no problem.

There's nothing obvious. I'm going to clean the ISV out and see if that helps (checked and it's definitely still working), but if it doesn't i'm not sure where to start looking next. If anybody's got any ideas, i'd love to hear them.


TIA!

Re: Rough cold starts

Reply #1 – August 12, 2025, 06:54:12 AM

Could be the blue temp sender.
It lets the car know when it's cold, to enrich the fuel etc.
Next time, try unplugging it when you're having issues.
If it does turn out to be it, don't buy a cheap one, there's a lot of dodgy pattern ones floating about on ebay.

Re: Rough cold starts

Reply #2 – August 12, 2025, 04:46:05 PM

Blue temp sensor is a good starting point. I would get one made by hella. Failing that check all the vacuum lines for cracks and the hoses from isv to the manifold and the crankcase breather including the rocker box bung to the inlet manifold.

Re: Rough cold starts

Reply #3 – August 14, 2025, 10:49:21 AM

Thanks for the advice. I haven’t had time to clean out the ISV yet but I did quickly check the blue temp sender.

The car is turning over a lot not too before eventually starting and running rough for a few minutes. I unplugged the sender to see what the start was like and it started pretty quickly but the idle was very erratic. Plugged it back in and I’ll settled immediately. Does this suggest a functional sender?

I guess my next steps will be CTS and O2 sensor?

Re: Rough cold starts

Reply #4 – August 18, 2025, 07:05:07 AM

Assuming you're in the UK, you won't have an O2 sensor.
They only put them in some European model back then for emission control.
The blue temp sender test does suggest it's feeding back a signal, whether it's the right signal, we can't be sure.
If it's not too expensive, I'd swap it out, just in case.

Re: Rough cold starts

Reply #5 – August 25, 2025, 08:44:26 PM

Ok so i've got the coolant temp sensor and blue temp sender on order and will replace them when they're in. The past few days it's started absolutely fine, though still runs a little rough until it's up to temp.

This evening i've gone to move the car, and it's just turning over and won't start at all. A couple of times it grumbled, definitely tried to start but just sat turning over forever. Hooked up the jump leads and it started. Now i'm even more stumped. Could i have a wiring problem somewhere maybe?

Re: Rough cold starts

Reply #6 – August 26, 2025, 10:07:33 AM

Hmm, could possibly be a battery issue?
Do you think the addition of the jump leads definitely fixed it, or just allowed you to turn it over long enough to fire?

Re: Rough cold starts

Reply #7 – August 26, 2025, 11:31:54 AM

I could turn it over indefinitely without the jump leads on, it just wouldn’t find enough energy to start it seemed. As soon as it was connected up to the other car it started, and this morning it started fine with zero delay.

I thought maybe a battery issue, but it is a relatively new battery. Has died a few times from sitting and me leaving the lights on like a numpty.

Re: Rough cold starts

Reply #8 – August 26, 2025, 12:43:16 PM

Hmm, my mates Rallye had a similar issue, went through loads of trials etc and in the end just put a new battery on and that fixed it.
Turns out it had 12v when idle and not doing anything, but as soon as you put a load on, while it would crank the engine, it dropped to about 6 and essentially turned off the ECU.

If you've got a known good battery, I'd try swapping it over.