Actually, it's probably adjustable with reference resistor. While you may not have the dial as it applies to euro vehicles in general, you might still have a connector with resistance plug on it. Different resistance values control the timing. This info applies to 6 cyl motors but I imagine it's the same for a 4. The second attachment shows the USA version.

Attached Files

	ref resist.pdf (41.3 KB, 457 views)
	ref resist USA.pdf (36.2 KB, 369 views)
	r16 values.pdf (25.8 KB, 397 views)