Have you checked your OVP? It seems alot of people are having trouble with this lately. It is located on the passenger side of the firewall. I have a '87 W124, so I think your '88 should be very similar to mine. Also do a search on OVP and there are plenty of discussions on how to inspect and change one. Good luck.

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95 R129
04 Infiniti G35.5 BS
10 X204