Surging idle and P0420 code

[texadelphia]

Last week my rig started surging pretty badly. When it was cold it would surge between 1500 and 2000 rpm and once it warmed up it would surge between about 500 and 1000 rpm. It's done the same thing once or twice in the past but would go away after a key cycle. Couldn't get it to go away this time until I disconnected the battery and let it sit for about 20 minutes. It mostly stopped but was still popping up when it was cold. Then today the CEL came on and it threw P0420.

At first I was thinking maybe the IAC needed cleaned or O2 sensors were bad causing the surging. Now I'm thinking maybe the MAF needs cleaned based on some things I'm reading about P0420.

Any other thoughts?

 

[det107]

P0420 code

 

[19963.4lsr5]

In my experience I only know of two or three things that cause the dreaded 420 code.

Exhaust leak before the cat cooling off the cat turning it off.

Burning antifreeze.

Driving around with a flashing check engine light from a missfire, melting the cat internals.


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[texadelphia]

I cleaned the MAF last week and cleared the code and it hasn't come back yet. It also hasn't been surging at all. It's still idling pretty high when cold though. I think my next play is to clean the IAC and see if that goes away.

 

[19963.4lsr5]

I cleaned the MAF last week and cleared the code and it hasn't come back yet. It also hasn't been surging at all. It's still idling pretty high when cold though. I think my next play is to clean the IAC and see if that goes away.

It will idle high and slowly go down to 750 in park as the engine warms up.


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[texadelphia]

Yeah, I know it's normal for the idle to be high when it's cold but it seems excessively high to me, like 2100-2200 rpm. Sometimes it will even creep up to 2500. I haven't checked the FSM for the spec though.

 

[19963.4lsr5]

Yeah, I know it's normal for the idle to be high when it's cold but it seems excessively high to me, like 2100-2200 rpm. Sometimes it will even creep up to 2500. I haven't checked the FSM for the spec though.

Does it idle at 750 warmed up in park?


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[brillo_76]

If its getting closer to 2500 rpm when cold starting. I would clean the MAF and clean the IAC.. Especially if you are noticing a sudden increase like that. Also check all the intake hoses etc for a vacuum leak.