loppy idle! Help!

[RatherBNtheWoods]

New engine(long block) has been running great for close to 30K miles now. It is great to have all new , good injectors etc...

Until about three weeks ago. The engine developed a quit lopy idle. Only when the engine is really good and warm/hot. And seemingly when the weather is hot.

Doesn't miss or cut out, and runs great when cold. But, after several miles, when I pull up to an intersection stab the clutch it lopes. You'd swear the cam had 50 degree of overlap. Shifter wobbles, tea glass sloshes etc... A couple of times it even died. Had to let the clutch back out(still rolling) to fire it back up.

No codes/lights or odd indications. If/when I rev it up just a bit it smooths out. High idle(PCM hooked up to upfitter switch #4) idles just fine at 1200 RPM.

No bucking, surging, missing or the like as long as it's above 1000 ish RPM.

Until today. The record heat finally broke, and today she idles real purdy like. No matter how hard or fast I run her she runs fine. WTH?

Fresh fuel, filters, oil, and the EGR stays unplugged so it's clean and closed.

When it's sitting at the intersection lopping, as soon as I start letting out the clutch and hitting the go pedal, she smooths out. Runs like a champ, boost swings right up to 30ish and is steady.

What/where do I need to check or smack?

[RatherBNtheWoods]

Anyone got anything?

[RatherBNtheWoods]

Today the tach fell to 0, but the engine was running fine. Where does the signal for the tach come from?

[flint_smoke]

My truck use to do the exact same thing. Ran great when cold but would idle crazy after it warmed. Mine turned out to be the wiring harness to the icp sensor. Wiggle that harness and see if that changes anything. It could also be the sensor itself.

[RatherBNtheWoods]

I'll check that. What about the tach? As soon as I cycled power(key) it came right back, just thinking the two is related.

[azkcr]

You Tube

You Tube

Like this?

[RatherBNtheWoods]

No. I think of that as more of a surge than a lope. Mine idles just exactly like my last hotrod gasser with a really tall, long duration cam. romprompromprompromp!

Tach doesn't surge up and down like in the video. Well maybe a little, but I can't see it with my old eyeballs. And she smooths out if I raise it too 1000 ish RPM.
No smoke etc...

And only after the engine gets really good and warm. Purrs when cold.

[flint_smoke]

Originally Posted by RatherBNtheWoods

No. I think of that as more of a surge than a lope. Mine idles just exactly like my last hotrod gasser with a really tall, long duration cam. romprompromprompromp!

Tach doesn't surge up and down like in the video. Well maybe a little, but I can't see it with my old eyeballs. And she smooths out if I raise it too 1000 ish RPM.
No smoke etc...

And only after the engine gets really good and warm. Purrs when cold.

Sounds exactly like what i had. You should definitely check out that icp sensor

[Clintd]

Coming from cummins the three things I would look into are the map sensor, cam sensor, and fuel rail pressure sensor. Thats if your ford even has those sensors. What your describing is how a cummins will act if any of those were bad. Try a search on those three sensors for your motor and see if anything comes up. Im just throwing that out there. Sorry i cant be more help. Im still learning the powerstrokes.

[azkcr]

Fuel rail pressure?