My brother is having a starting problem with his 1997 Golf (1.8L). It starts great when it's cold, the problem is when it's warmed up and then shut off for only a short while. Sometimes it will take minutes of cranking to get it started and then he has to keep his foot on the gas to keep it going. It's also harder on gas than usual. Any ideas?
The temperature gauge is working normally (goes up to the halfway mark and stays there). He tried a temperature sensor from a parts car and it didn't make any difference. When it does start he said you have to play with the throttle to keep it running for a while and sometimes it idles way up and down for a while after it starts.
The gauge has nothing to do with it. That's a separate sensor. There is a CTS (coolant temp sensor) that's likely to be the problem. That's what needs replacing. It's not expensive. Usually mounted on a flange and just has a clip holding it in place.
It's also possible your O2 sensor is failing. That's easy to troubleshoot. Just disconnect it. That puts the car into open loop mode. Drive it for a day or so and see if the problem goes away. If it does then the O2 sensor is bad.
Another possibility is the MAF. You can try dumping half a can of MAF cleaner into it. That often helps.
Oddly enough, another possibility is the air filter. Check that.