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2000 Avalon
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155 Posts
Discussion Starter #1 (Edited)
A friend's car. P0300, P0301 original issue. Checked coils, they had oil on the boots, and fouled plugs. I replaced the valve cover gasket. One coil was dead (cyl #1). I replaced it from one from NAPA. Codes were gone.

Then P0171 came up. I live streamed data and the MAF sensor was not operating correctly. Replaced MAF sensor. Code is gone.

P0300/P0301 keeps coming back, intermittently. Now you see it, now you don't. Injectors show correct resistance, and "click" when listening with a stethoscoppe. Smoked intake manifold, no leaks. Cylinder 1 plug is oil "wet" but not fouled. Other plugs are fine. Car has 168K on it. Next up is a compression check, but why this is intermittent is a puzzle. IAC valve is giving normal readings. I cleaned the throttle body and the owner had a shop do an injector cleaning and ran sea foam through the throttle body, but the code returns. Delete it, and it comes back in a week or two. Car seems to shudder slightly when cold and the AC is turned on. I live streamed AC idle circuit and it increases RPM when the AC turned on, as it should.

Any ideas on what to look at next? Thanks!
 

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2000 Avalon
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155 Posts
Discussion Starter #3 (Edited)
I installed the new one and it works. It was a NAPA branded part and wasn't cheap ($75). Strong spark jumps to a test ligbt. I put new NGK iridium plugs in too. I suppose I could get a denso coil and try that, but i don't see how replacing a part that works will solve the problem.
 

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2000 Avalon
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155 Posts
Discussion Starter #5
No, that coil on plug was dead, dead, dead. I tossed it, and put a new one in. If I pull the new one, it sparks fine.
 

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Discussion Starter #7
That sounds like a good idea. I will swap #1 with #4 and report back.
 
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