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I have a cel for 22 knock sensor 33 speed sensor And 42 idle switch? When I let off the gas the car shakes and shutters and it has a rough idle. It's a 92 legacy turbo manual transmission. Where should I start is there any known issues that would throw these 3 codes?

The speed sensor code is for your spedometer. The ECU is not seeing a vehicle speed sensor (VSS) so it's throwing a code. 22 is knock sensor, those are pretty common. Pull yours out and check it for cracks, and check the wiring/plug as well. 42 is the Idle Switch, it tells the car when your in throttle, and when you're not (at idle), if that is not calibrated the car will act very weird. The idle switch is intergrated into the TPS sensor on the throttle body. Your car has a 4 wire TPS (throttle positing sensor) and the brown wire is for the idle switch. Check that plug and make sure that it looks ok.

It is good practice to start with the lowest number code first, reset the ECU, and see what comes back. I would suggest resetting the ECU anyway and see what codes come back.

If I had to guess I'd lean towards the knock sensor. If your speedometer works, then the VSS should be good. Check out the bottom of this thread for how to check the idle switch.

http://bbs.legacycentral.org/viewtopic.php?f=5&t=53308

Thank you I reset the ecu and it has not thrown the codes again so far. The speedo works fine and I will look at your link about the idle switch.

As long as it hasn't thrown any codes, you should be all set.