Chasing a rough idle
05-02-2021, (Subject: Chasing a rough idle ) 
Post: #1
Chasing a rough idle
Looking for some help from the OG ISX group...

I've got a CM871 with a rough idle problem. Engine idles fine when cold/cool but once it warms up it has a rough idle with noticeable intermittent fuel knock. Under any kind of load the engine runs butter smooth.

Monitoring with Calterm you can see the timing erratically jumps between -1 and -11 degrees at idle when the rough idle occours. Funny thing is if you put just even the slightest load on the engine (A/C on w/ engine fan on) it will smooth right out and timing will stabilize.

Cutting off 1 cylinder at a time doesn't lend any information as it introduces just enough of a load that it smooths out no matter which cylinder or group of cylinders you deactivate.

I've monitored various sensor readings and they all report correct for conditions.

I'm leaning towards actuators at this point but am truthfully stumped. Any input from the group? TIA
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05-02-2021, (Subject: Chasing a rough idle ) 
Post: #2
RE: Chasing a rough idle
i'm following here,not there
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 Thanks given by: 389driver
05-02-2021, (Subject: Chasing a rough idle ) 
Post: #3
RE: Chasing a rough idle
Something I forgot to add...

When I monitor fueling rate and timing on a graphical screen, they mimic each other almost perfectly. One does not precede the other though, so it's hard to determine if one is influencing the other.
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