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Start with the basics. When was the last tuneup (time and distance)? Besides the air and gas filters, within the last 15K to 20K miles, have you replaced the spark plugs, distributor wires, distributor cap, ignition rotor and PCV valve? If not, do those.
Also, since both code 15 (no speed sensor signal) and code 21 (lazy O2 sensor) show up, there's a good chance that there is a wiring/connection problem. How long has the car behaved this way? Was it this way when you bought it? Oxygen sensor is ignored by the computer at cold starts, for about 2+ minutes, and EGR does not function with engine cold. So those are not causing the poor cold operation (unless the EGR valve is stuck open; but then you'd get a rough warm idle).
Check the ground connection at the driver's side rear corner of the block, where a ring tongue terminal from the wiring harness bolts to the block. The wire often gets frayed or cracked, or breaks. This is the ground for many of these sensors.
Also, check carefully at the battery. Don't just give it a visual, disconnect the battery, clean the posts and terminals with a brush, and inspect the cables where they exit the clamps, for corrosion, bad insulation, loose strands. Check the battery voltage with everything off (should be about 12.4V or higher) and at idle (should be about 13.7 to 14.0 volts).
In addition, check ALL rubber and plastic hoses and lines for cracks or breaks - power brake booster line, PCV hoses, and all the vacuum lines.
Finally, check the braided ground strap between the passenger side firewall and the intake manifold. This is another ground that will cause issues if not solidly connected.
Report back what you find and we'll go from there. If that doesn't do it, there are some other plugs at the computers to look at. And welcome to Allpar!
Also, since both code 15 (no speed sensor signal) and code 21 (lazy O2 sensor) show up, there's a good chance that there is a wiring/connection problem. How long has the car behaved this way? Was it this way when you bought it? Oxygen sensor is ignored by the computer at cold starts, for about 2+ minutes, and EGR does not function with engine cold. So those are not causing the poor cold operation (unless the EGR valve is stuck open; but then you'd get a rough warm idle).
Check the ground connection at the driver's side rear corner of the block, where a ring tongue terminal from the wiring harness bolts to the block. The wire often gets frayed or cracked, or breaks. This is the ground for many of these sensors.
Also, check carefully at the battery. Don't just give it a visual, disconnect the battery, clean the posts and terminals with a brush, and inspect the cables where they exit the clamps, for corrosion, bad insulation, loose strands. Check the battery voltage with everything off (should be about 12.4V or higher) and at idle (should be about 13.7 to 14.0 volts).
In addition, check ALL rubber and plastic hoses and lines for cracks or breaks - power brake booster line, PCV hoses, and all the vacuum lines.
Finally, check the braided ground strap between the passenger side firewall and the intake manifold. This is another ground that will cause issues if not solidly connected.
Report back what you find and we'll go from there. If that doesn't do it, there are some other plugs at the computers to look at. And welcome to Allpar!