Where to find and what to actually do with the 1987 Audi 90 owner's manual
The 1987 Audi 90 is a C3-generation platform car, essentially the sedan version of the Audi 5000 that ran from about 1986 to 1991 in various markets. The owner's manual for that model year is a fairly thin booklet, usually around 40 to 60 pages depending on the trim level and destination market. It covers basic operation, fluid capacities, the dashboard warning lights, and the scheduled maintenance schedule. That is about it. It does not contain repair procedures beyond things like bulb replacement and wiper blade changes. The most reliable free source I have found is the ManualsLib page for the Audi 90. It has the PDF uploaded by a user named "audi-docs" and is the 1987 US-spec version. If you are looking for the European market version, that one is harder to track down cleanly. Another route is the Audizine forums. Members occasionally post high-scan copies in the Classic section. You can also check eBay if you need a physical copy in decent shape. They run anywhere from fifteen to forty dollars used. I have printed the ManualsLib version on A4 paper and it scans well enough. The text is small but readable at standard font sizes. The diagrams for the fuse box and the instrument cluster are the parts you will actually use regularly. Everything else is mostly reference material for annual inspections and fluid checks.
What the manual actually tells you to do
The 1987 Audi 90 owner's manual is organized in the standard German automotive fashion of the era. It starts with an introduction to the controls, then moves into the instrument panel, driving tips, fuel recommendations, maintenance intervals, and a troubleshooting section. The maintenance schedule is the part most people skip, but it is where you get the oil change intervals, spark plug types, and belt replacement windows. The oil capacity for the 2.2-liter five-cylinder engine is approximately 5.0 liters with filter change. The 2.3-liter five-cylinder that some markets received holds about 5.5 liters. The automatic transmission fluid capacity is roughly 4.5 liters for a drain and refill, though the total system capacity is closer to seven liters if you remove the pan. The manual does mention the Dexron II specification for the 4-speed automatic, which is still the correct fluid today unless you are doing a full conversion to a synthetic alternative. The spark plug gap is set at 0.6 to 0.7 millimeters for the five-cylinder engine. The official plug type listed is the Bosch W7RTC or an equivalent NGK or Denso part. If you are maintaining the car yourself, writing down the part numbers from the manual before you shop saves a trip to the parts store. The manual also lists the timing belt interval at 60,000 kilometers or four years, whichever comes first. That interval is aggressive by modern standards, but it is accurate for the era and the belt materials Audi used at the time.
A realistic problem I ran into and how I fixed it
My '87 Audi 90 had an issue where the turn signals would work normally when cold, but after about twenty minutes of driving they would slow down dramatically, like a solid four blinks per second instead of the usual ten. I replaced the flasher relay twice before I realized the manual's diagram for the fuse box layout was slightly misleading on the labeling. The turn signal circuit shares a ground path with the brake light switch on the C3 chassis, and that ground point is located behind the left side of the dashboard, near the steering column. The workaround was to clean the ground strap connection at that point, which took about twelve minutes with a small socket set and some contact cleaner. I also applied dielectric grease to the connector pins. The problem has not returned in over a year. The manual does not mention this ground point at all. It lists the fuses and relays, but not the chassis grounds. That information is in the electrical wiring diagrams, which are separate from the owner's manual. If you own one of these cars, getting the factory service manual with the electrical section is worth the effort.
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Common misunderstandings about this manual
People often confuse the owner's manual with the service manual. The owner's manual will not tell you how to remove the cylinder head, adjust the valve clearance, or bleed the braking system. For that you need the factory service manual, which is available through Haynes for the Audi 90/5000 platform. The Haynes manual covers engine overhaul, suspension work, and electrical diagnostics in much more detail. Another misconception is that the fluid specifications in the manual are absolute. They are not. The manual lists what was available at the time of publication, but some of those specifications have been superseded. For example, the manual recommends 5W-40 conventional oil for the five-cylinder engine. Modern synthetic 5W-40 or even 5W-30 formulated for German engines is acceptable and often preferable, especially in colder climates. The manual also lists the coolant as a green ethylene glycol mixture, but the current recommended specification is G12 or G13, which are pink or violet in color. Mixing old green coolant with newer formulations can cause gel formation in the passages.
What the manual leaves out
The 1987 Audi 90 owner's manual does not cover the Quattro system in any depth if your model has it. It mentions the center differential lock button on the dashboard, but it does not explain how the Torsen center differential works or how to service it. The manual also omits any information about the cabin air filter, since the C3 Audi 90 does not have one. People sometimes look for a location that simply does not exist. The diagnostic port section is minimal. The OBD-I system on the 1987 Audi 90 uses a two-pin test connector under the dashboard near the fuse box. The manual tells you to short those pins and read the flash codes on the engine management light, but it does not list what any of the codes mean. You need a separate code chart or a diagnostic tool for that. The flash code system is not standardized across all markets either, so a code that means something in the US spec may be different in a European spec car.
Practical advice for using the manual
If you are working on the car, keep the manual in the glove box but also print out the maintenance schedule and the fuse diagram. Those two pages get the most wear. The rest of the manual is reference material that you will look at maybe once a year during pre-trip inspections. The fluid capacities and specifications pages are the ones to photocopy and keep in a work folder. The paper in the original booklet degrades over thirty-five years, and the glue binding tends to fail. For the owner's manual itself, the digital PDF is fine for quick lookups. If you want a physical copy that will last, search for a replacement booklet on eBay and buy the one with the least creasing. The spine on these tends to crack within the first five years of ownership, and the pages fall out. A plastic sleeve or a three-ring binder works better for long-term storage than the original binding. The 1987 Audi 90 is a straightforward car mechanically, but the electrical system has quirks that the owner's manual does not address. Knowing where to find the information beyond the manual is what separates people who can maintain these cars themselves from people who hand them off to specialists for everything. The manual is a starting point, not the final word on any subject.
