Rough Idle

[Jareb]

85 300TD 320,000mi

Great original car; always serviced, that runs smooth and strong. Burns very little oil; maybe 1/3 qt between changes.

After a long highway run{4 hrs.} at 75-80 mph; the car will idle pretty rough when coming off the interstate into city traffic at the stop lights. It idles like this for maybe 5 miles of regular city street driving; then it smooths out and runs like it always has. Kinda weird.....any ideas about this?
Thanks
John

[Diesel911]

Originally Posted by Jareb

85 300TD 320,000mi

Great original car; always serviced, than runs smooth and strong. Burns very little oil; maybe 1/3 qt between changes.

After a long highway run{4 hrs.} at 75-80 mph; the car will idle pretty rough when coming off the interstate into city traffic at the stop lights. It idles like this for maybe 5 miles of regular city street driving; then it smooths out and runs like it always has. Kinda weird.....any ideas about this?
Thanks
John

Some thoughts on that:

Valve Adjustment

Your idle rpm (on one of your emission stickers is the proper idle rpm)

I had a small Air leak that only showed up when the Engine was hot. The Fuel Inlet Hoses were too inelastic and hard and they did not seal well even though the clamps were tight.

If the Governor Idle/Rack Damper Pin is not the latest one a new one may have a good effect on the Hot Idle. However, in My Case rebuilding the Injectors and the Valve Adjustment took away the bulk of the Shaking.
New Motor and Transmission Mounts took away more.

At the end of that the Governor Idle/Rack Damper Pin was able to get rid of a little more shake.

Note: Being new to the forum I read up on the shaking issue and many recommended the new Gold Rack Damper Pine. I bought one thinking that was going to cure it. But, it did not.
My conclusion from all the stuff I had to do or fix to cure the shaking was is that the Rack Damper Pin is there to take away some shaking from Engines (like a new Engine) where everthing else is within specs.

My particular case was not the same as you describe. Mine started shaking after about 10 minutes driving even in City Traffic and it did not go away until the Engine was shut off and the Car sat long enough for the Engine temp to go down.

Other possibe issues.
The bulk of the Diesel Fuel going into the Fuel Injection Pump is used to cool the Fuel Injection Pump and then it returns to the Fuel Tank. So after you drive a while you have a tank of warm to hot Fuel.
When the Fuel gets Hot it gets thinner.

I am thinking that if you pull off of the Freeway and everthing is nice and hot and you have some issues with your Fuel Supply/Lift Pump and or your Fuel Pressure Relief/Overflow Valve the hot thin Fuel could have an effect on the Fuel Delivery.
To detect that you might have to Drive till you have the Symptoms and check the Fuel Pressure at idle.

I don't know for sure but I think part of the Injector issue was caused by the tiney drilled passages in the stock Injector Nozzles being plugged solid with Carbon. I can't verify this becasue I did not clean the Carbon out and try the Nozzles.
However, I do know that replacing the Nozzles and setting the opening pressures took away a big chunk of the Shaking.

[Brian Carlton]

The SD is doing the exact same thing at 265K.

However, it may or may not improve after 5-10 local miles. It improves, but never gets "smooth".

As soon as I can get the SE in service, the nozzles will be replaced with Monarks on the SD.