Rough Idle With Truck In Gear

Sorry if this is a repeat subject, but I haven't looked at the BB for a long time. A couple days ago I was dropping a friend off at his house, truck stopped, in gear, and the idle became very rough. Put the truck in Park and the idle smoothed out. Tried again in both Drive and Reverse, same thing idle became very rough again. Once I gave the truck a little throttle it smoothed right out. Drove home about 15 miles and the truck has not missed a beat since. Never got a SES message, so I don't know what caused this problem. Didn't know if this was a condition that has been discussed on the forum so I thought I would ask about it.
Thanks for any info you might have.
angus

I am assuming you have an LLY. If so, have you had the reflash done? My tuck started soing this last May. The dealer was unable to diagnose. I quick email to a GM VIP got me a phone call from a Bill Carnabelli(sp). Bill is the Duramax Quality Manager. He instructed the dealership on how to diagnose. They were doing tests on the injector calibration with the truck in park. The same as your truck, it was fine in park. When the truck was put in gear, the specs went out on one of the injectors. He ordered all injectors replaced. At the time he told me that they were expecting a software fix within a few weeks. It took closer to two months. The reflash is supposed to correct this. I had mine reflashed after the fact just to see if it made any differance. So, if you have an LLY and have yet to get the reflash, then call your stealer and ask for it. I believe it will correct your problem.

LB7 or LLY? what exaclty do you mean by ROUGHNESS???? surge, misfire, low idle, etc....? LB7 FPRs are a fairly common failure and there is a bulletin out on loose crankshaft reluctor rings for LLYs. The FPR causes more of a surge while the loose ring will cause both a surge or low idle.

Thanks for the response. The truck is an LLY, and I have not had the re-flash done. The roughness that I felt was like a miss, It acted like the motor was about to die, very lopey. Since that instance three days ago the truck has run fine. Unfortunately I'm about two hours from the nearest GMC dealer, so I don't know when I can get the truck in to be re-flashed.
Thanks again
angus

check the ground on the lower right side of the engine block. other then checking that it really needs to go to the dealer.

HOW DID YOU GET THE EMAIL ADDRESS OF BILLCARNABELLI?
MIKE

Just had my 2004 LLY in for service due to rough idle and surging while in gear. It would also smoke like heck while this was happening. Diagnosis was 2 bad injectors along with a bad fuel pressure regulator. Only been a week but no reoccurence yet.

Can I get the code?
Glad to see this topic, last week, 3k mi. on my 04 LLY and it started the same thing, rough idle in gear, etc. Engine light came on, then it all cleared up. It went in a couple of days ago to the stealer for my first free L.O.F. they said the gas cap was probabaly loose! Well tody it all came back-WORSE. At light throttle (1500 rpm, 50 mph) it's shuddering to the point of rattling things in the cab. The light is on again as well. It will make a visit to you know who asap, but in the mean time: Can I get the code from the light? My older trucks could blink the light if I crossed a couple points on the diag. plug. Anyone know if this can still be done?

04 LLY crew 2500HD
RV HAULER

Quote:

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Originally posted by movemyrv:
Can I get the code?
Glad to see this topic, last week, 3k mi. on my 04 LLY and it started the same thing, rough idle in gear, etc. Engine light came on, then it all cleared up. It went in a couple of days ago to the stealer for my first free L.O.F. they said the gas cap was probabaly loose! Well tody it all came back-WORSE. At light throttle (1500 rpm, 50 mph) it's shuddering to the point of rattling things in the cab. The light is on again as well. It will make a visit to you know who asap, but in the mean time: Can I get the code from the light? My older trucks could blink the light if I crossed a couple points on the diag. plug. Anyone know if this can still be done?

04 LLY crew 2500HD
RV HAULER

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The codes can only be read with a scanner on 1996 and later GM vehicles, which are OBDII. The 1995 and earlier OBDI vehicles are easily read with a paperclip and a little time, and it sounds like you are familiar with that. Your truck should still be under warranty, let the dealer deal with it.

DMAX MAVERICK:
Thank You for the update on getting codes. I am all over the warranty issue with only 3K miles! I was more curious than anything about the do-it-yourself code read. I assume the codes will hold in history even if the light clears? That happened last week.
Thanx again.

Update,
Code is 1229, apparently means bad feedback info from injector 3. They said leave it off for a couple days to "tear down that side of the engine" they don't seem to have much diesel experience (oh boy!) in the mean time, of course the light is out and the truck runs great again. I asked if reflash of the computer would be included in the two day tear down, they said, oh maybe we could try that first! Hope they don't mind if I look for a more experienced shop.

on an LLY there shouldn't be much "tear down" to it. I've seen this code by it's self one time, never could duplicate it myself. TAC had me put a FICM on it and it hasn't reoccured since. I've seen this code set the most w/ three other 1200 codes when the engine has lost a "group"(1,4,6,7 or 2,3,5,8)of injectors. All three times I've seen this I diagnosed the FICM as being bad and none have had a problem since. their complaints were SES light and poor performance.

Thans Again for the input and advice, it goes in friday for a work-up. i will update if anything significant happens.