05 swinging idle and stumble @ 29% load

[Mountainman234]

My 05 6 speed has developed an idle condition when retuning from any throttle above idle.

When coming down it will drop past normal idle speed of 800 and plunge as low as 500 sometimes, then swing up to 9-950 and drop back in lessening swings until it settles at 800. All in the time of a stop light. This will happen cold or hot and has been intermittent but is becoming more frequent.

It has also on occasion had a low rpm start of 4-500 rpm then jumped up 800 within 3 seconds of a cold start. This is intermittent currently.

Finally it also has a stumble at 29% load. Doesn't matter the gear or the speed or the throttle position. It's more prominent when loaded heavy. If u go above or below that, it's fine. Rail pressure is steady, lift pressure is good, rpms dont even change.

The engine has 50,000 miles but the cp3 and the rail etc, have 290,000 original miles. The injectors have 20,000 miles and are 85% over s&s diesel, with a fass 150 lifting with fresh filters. It's currently running smarty TNTr tuning with udc capability, I have yet to mess with udc. I'm watching it all with edge insight cts2.

I'm getting good mileage and am otherwise quite happy. Just need to figure this out, the little quirks bother me. I suspect either the rail or the cp3. I don't want to just throw parts at it thou.

Thanks for any input, Ben

 

[Timbeaux]

You monitoring RP during the issue?

 

[Mountainman234]

Yes I am, rail will fall to maybe 6200 and bounce around during the idle swing, it doesn't fluctuate when stumbling at 29% load.

 

[Mountainman234]

Bump

 

[59turbo]

I'd try to put a scan tool on it to monitor commanded rail pressure vs. actual during the idle fluctuation. Any fault codes?

 

[Mountainman234]

Will do, hadn't thought of that. No codes.

 

[xDiesel03]

What's your TPS reading when this occurs?

 

[Mountainman234]

3%, same as it has been

 

[chris lang]

What pump are you running with those injectors and have you tried retuning it to stock tune?

 

[Mountainman234]

It's the stock pump, the mileage on it is in my op.

Couple days back I ran it on stock tunning for a bit.

The stumble @ 29% was gone, I then ran it with the old tune and higher rail pressure than before and it was worse. So it's a tunning problem I'll have to work out with UDC. I'd say.

The idle swing was still there but much less noticeable than before. With the same higher rail pressure tune it is also more aggressive than before. So I'm not sure what's causing this still.