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Intermittent check engine light

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I have been getting an intermittent check engine light lately with my EJ22 NA, auto box (ugh). Last night it came on and I emmediately pulled of into a Wendy's lot and checked all the fluids. The oil is at proper level, exactly at the divet for "hot" full, the coolant is fine, and the engine was not making any sounds like a knock or anything. The light stayed on while idling, but after I turned it off and restarted the light did not come back. The idle has been varying slightly lately, like +/- around 100rpm, but not too much. It is smooth as ever. Could this be due to a dirty O2 sensor, or MAF? Thanks in advance, I really don't want to pay a shop to do a OBDII scan.

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Check all the ground cables, undo and tighten them back to spec. Loose grounds can give funny problems.

 

That, or you knock sensor is cracked. Have a look from above, should be able to see it below the rear of the intake manifold.

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If it's just comming on sporadically, it sounds like an electrical connection problem - ground problem, or shorting out.

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On my 93 Legacy, my check engine light comes on when I stary the car, only about 1 out of every 100 starts. If I immediately turn the engine off and restart, it doesn't light up. Any ideas?

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I have been getting an intermittent check engine light lately with my EJ22 NA, auto box (ugh). Last night it came on and I emmediately pulled of into a Wendy's lot and checked all the fluids. The oil is at proper level, exactly at the divet for "hot" full, the coolant is fine, and the engine was not making any sounds like a knock or anything. The light stayed on while idling, but after I turned it off and restarted the light did not come back. The idle has been varying slightly lately, like +/- around 100rpm, but not too much. It is smooth as ever. Could this be due to a dirty O2 sensor, or MAF? Thanks in advance, I really don't want to pay a shop to do a OBDII scan.

You need to check the codes as Josh says. A faulty temperature sensor can bring up intermittent check engine light. In my case it occured about 5 minutes after start up and was up for about 3 minutes. However when I checked the resistance of the sensor it appeared to be within specification. This went on for about 6 months before it finally caused a problem by latching up all the radiator fans.

Perhaps this is the cause of your rough idling also. It is one of the transducers that causes hard starting.

Regards

Peter

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Thanks for the input guys. I just got a Chiltons for this car, which I think is the second gen, or the facelifted first gen; not sure. Was 95 on third gen? Anyway, I will take a look at the knock sensor, which seems actually to be doing a crappy job; I think I can hear audible ping on 85 octane and warm weather. It could be slap, but I think not. Nevertheless, if it recurs I will go to Autozone if it happens off the job.

 

Thanks,

Roy

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