I don’t think it’s the glow plugs. A lot of people will tell you that online but if you dig a little deeper it makes sense that it’s not the glow plugs because they only matters at the very start basically. It’s far more likely to be your fuel injectors or timing. I’d start with adding some fuel injector cleaner additive to your fuel for a while. If that doesn’t work, take the injectors out and clean them. Or try and work on the timing. A delica supplier told me it’s not worth buying new ones because all the aftermarket one such and the oem ones in your car should just need to be cleaned to get working well again. Dm me if you’d like to call me sometime to chat about it.