Below is the coolant flow direction of all the piping and equipment on a M20 engine.
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Most publicly available fuse layouts are perfectly fine, but for those who want reassurance, the below is the layout described in the factory E30 repair manual.  
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Early and Late E30 fuel systems mainly differ by the fact that early runs a two pump system and late runs a single pump. With that primary difference, routing of fuel lines and vapor lines is also notably different.   Early:   Late:
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Below is the factory pinout of an E30 Cluster:
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Normally, we are told to fill AC systems by weight. That is normally because pressures change greatly depending on temperature. These seldom seen AC pressure charts allow us to directly cross check and test our systems for optimal performance.    
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There are numerous OEM E30 spring part numbers, and the below is the breakdown of what net effect each will have on ride height and how they interrelate with what options you may add or subtract in your E30.  
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E30 Factory manual pinout and illustration showing the routing of the central locking system found on E30’s:    
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This is an excerpt from the factory E30 repair manual instructing how to mechanically and electrically test the ICV (idle control valve) for an M20 engine.
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In the vast majority of cases, vacuum leaks are to blame for poor or inconsistent idle issues on M20 engines found in E30’s. Vacuum leaks basically mean air that is entering the engine where the air flow meter has not had a chance to meter it. Unmetered air, is unexpected air, and as such...
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These CNC ICV elbows replaces your stock ICV elbow. The original elbow is press fit from factory and loosens over time. Once loose, you end up getting a vacuum leak and up until these there was no great way to solve the problem. Most people either try a glob of JB weld or silicone;...
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