Shahabidabi Posted June 9, 2010 Share Posted June 9, 2010 I have a 90 Legacy, the check engine light comes on and off at random times. It will be on when I start the car and will go off when driving down the road, no loss of power, no weird noises, no changes to driving in any way other than when the light turns off it makes the car jerk once. Has anyone else run in to this problem or have an idea what might be causeing it? Link to comment Share on other sites More sharing options...
Legacy Wagon Posted June 9, 2010 Share Posted June 9, 2010 No clue, but someone on here recently posted how to read OBD1 codes. You could always check it out when the light comes back on, but keep in mind the car is 20 years old. Gonna have it's quirks Link to comment Share on other sites More sharing options...
fkyx Posted June 9, 2010 Share Posted June 9, 2010 The ECU stores codes. So even though your CEL isn't on, you can still pull any existing codes. What I would suggest is you unplug the negative terminal of your battery over night (to clear the codes), then drive the car around a little the next day (to bring back any codes that still exist), and pull the codes (if any) when you're done. Link to comment Share on other sites More sharing options...
Legacy Wagon Posted June 10, 2010 Share Posted June 10, 2010 I wasn't aware OBD1 did that. I've also never had any CEL's on though in this car. Link to comment Share on other sites More sharing options...
Platinum_Racing Posted June 12, 2010 Share Posted June 12, 2010 http://legacycentral.org/library/literature/codes.htm The article was on LegacyCentral, posted by sqc151. I had a similar issue. I suspect it was the IAC, seeing as how the car had much trouble starting until you gave it some throttle, and the temp sensor, since the cooling fans would be running full blast 100% of the time for no reason. These issues happened 2 winters ago and miraculously went away on their own before I got the chance to investigate. I had the issue for about 2 weeks. Both issues came and went simultaneously, and I haven't seen either one since. +1 for what fkyx said though. If they do come back after the ECU reset then you know something is actually wrong. With my issue they came back, but at the time I didn't know how to read the codes. Eventually they went away, luckily before I started dumping time, money, and parts into it. Link to comment Share on other sites More sharing options...
ehsnils Posted June 12, 2010 Share Posted June 12, 2010 Do the simple things first checking hoses and similar. And reading codes can give you a hint. The "bump" when it comes off indicates that it changes from a "safe" mode to "normal" mode, and that indicates that it suddenly gets some more power. That may indicate that there is something that can impact engine power - O2, EGT or knock sensor. Link to comment Share on other sites More sharing options...
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