Golf 1997 takes time to start...

I have a manual 1997 1.8l golf. The car starts without problems most of the time but it happens sometimes that I would turn the key, the engine will start for 2 seconds and die. Then I try to start it again but it does not want to. Seemed to me like a gas alimentation problem. The problem started this winter so I changed the gas filter and the spark plugs. All the wirering has been replaced 3 months ago but the problem is still there. Is there any gas regulator on that car? and if so could it be the problem?

I have another problem that can be related to this one. The temperature gage was always staying under 70 degrees celcius. I brought it to a garage and they changed my thermostat and my temperature sensor. After they tried it the temperature indicator was still indicating the same temperature as before. The mechanic told me that it was probably my dash that was in problem and that is wasn't a big deal since they changed the temperature sensor and the thermostat and since the fan was working well.

Does anybody know what is my problem?
If I forgot some info tell me and I will give more explanations!

ThanK You!!!

Check the mass air flow sensor and try to clean it also check the throttle body and intake tube for oil residue and clean with throttle cleaner. 2.0L and 1.8L 8v engines have issues with the pcv valve rubber diaphram cracking and letting oil into the intake and fouling the maf sensor.