Rough Idle

[MEP]

I was sitting at a stop light on my way home from work this PM and my D-Max stared to idle very rough. Like it was only running on 4 cyls! Any speed above idle, the truck runs fine. If I touch the accelerator lightly with my foot, not even enough for the tach to register a speed increase, the roughness goes away. I checked under the hood and every thing looked ok. This problem is present with or without the AC on. I suspect the problem is with the accelerator rheostat.
Anyone else have this problem?

2001 2500HD W/ZF-6 spd. 23,485 miles.
Jim B, member #739

[7mmSTW]

Ours seems to have the same symtpoms, we just noticed it this weekend. My dad told me about it and I drove it all day today and it seems to do just the same thing. Kind of like a miss at idle but smooth all of the way past idle.

Later

Seven

[NutNbutGMC]

^...Do a search on "Lopey Idle". There is a fix for the problem.

[crafty]

I have the same problem as well. It has only happened on 3 occasions in the last month. I think this is different than the "lopey" idle that was mentioned before. With that you could see the tach change rpm's while idling. I wondered if it had anything to do with an injector miss firing. If I can get it to do it more often I will show the dealer. For now I will keep an eye on it. The first time it happened, it went away as soon as I released the clutch a little to put load on the engine.
If I find anything new, I'll let you know!
:rolleyes:

[MEP]

Sorry for not getting back earlier with more info on this "rough idle" problem, but a contractor drove some sheet piling thru a fiber cable in Boston and knocked me (and thousands of others) off the net.
This is NOT the lopey idle problem. I have that problem and it does not bother me. This problem only appears when the vehicle stops moving and is at rest, such as stopping at a stop sign. The idle is so rough that the shifter shakes left to right. (I have a manual box). As soon as I touch the accelerator or the truck starts rolling, the problem goes away and the truck runs fine. I can stop on a hill in neutral or with the clutch in, and as soon as the truck stops the idle get rough. When I take my foot off the brake and the truck starts to roll, the idle smooths out while the RPM remains at approx 650. The speed at which this problem appears/disapears is approx 1 MPH.
My first post I stated that the cause may be w/ the APP (accelerator pedal position sensor), but now I believe its in the VSS (vehicle speed sensor) circuit. All my accesories work fine, specifically cruise and AC, there is no engine knock, strange noises or taile pipe smoke. Just a rough idle and a lot of engine shake. I also have no MIL (malfunction indicator lamp) postings.
I have an app. w/ the dealer next week. Wlll keep Forum posted on results.
JB, member #739
PS, After I send this post I'll be shutting this PC down and hooking up a new computer, so I may be off line a while. (New system: P4, 2.53 W/533 FSB etc.)

[WayCoolKennel]

Hey MEP.. did you ever find a fix for this ?? I Think mine has a similar problem.. but it is so slight.. I'm afraid to take it to the dealer.. (truck only has 1k miless) might get laughed at ;)

Truck otherwise runs perfectly... hmmm..


--Steve

[crafty]

About two weeks ago I was lucky enough (or not) to have the rough idle problem show up while I was in the vicinity of the dealer. I stopped in and had the Diesel tech take a look. He has not seen this problem before and has no idea what the cause was. He took a "snapshot" of the engine with the scan tool and sent the following printout to GM for their feedback. Asd of a few days ago there was no answer from GM Canada.
Does anyone have a similar printout of their truck?
I'm open to any suggestions!

Egine speed 620 rpm
APP indicated angle 0%
Caqlculated fuel rate 5 mm
Fuel temperature sensor 57 C
Actual fuel rail pressure 33.6 MPa
Desired fuel rail pressure 34.0 MPa
FRP regulator command 34%
Main injection timing -2.0
Injector 1 command 0.31 ms
Injector 2 command 0.00 ms
Injector 3 command 0.53 ms
Injector 4 command 0.14 ms
Injector 5 command 0.00 ms
Injector 6 command 0.49 ms
Injector 7 command 0.50 ms
Injector 8 command 0.56 ms

Balancing Rate Cyl 1 -1.4 mm (squared)
Balancing Rate Cyl 2 -7.0 mm
Balancing Rate Cyl 3 5.2 mm
Balancing Rate Cyl 4 -4.5 mm
Balancing Rate Cyl 5 -7.0 mm
Balancing Rate Cyl 6 4.3 mm
Balancing Rate Cyl 7 4.3 mm
Balancing Rate Cyl 8 6.9 mm

Engine run time 00:01:32

:confused: :confused: :confused:

[ 07-11-2002: Message edited by: crafty ]

[ 07-11-2002: Message edited by: crafty ]</p>

[WayCoolKennel]

Dont listen to me... I must be paranoid ;) mine RUNS like a TOP !

;)

[MEP]

I have not forgotten the Forum in regards to posting the cause of my trucks "rough idle", but because of my schedule and the holidays, I was only able to drop my truck off @ the dealer last Monday (Jul 15). They said that they will get to it tomorrow. (yeah right)
The problem is still there and it only happens @ IDLE when the TRUCK is NOT MOVING.

JB member #739.

[crafty]

7mmSTW & anyone else that thinks their truck has this rough idle problem...is your truck a 6 speed?
If so I may have found the cause. Please post whether you are driving a Standard or auto ASAP and I will get back to you. The tech from the dealership called today asking me more questions so I need to find out if any Autos are doing this.

Thanks

[DucksnDiesel]

Yes, mine has it and I have the Allison (18K miles). It will do it one or two days a week. It is not consistant enough to take in for service yet.

[mackin]

How rough is rough? Mine isn't smooth all the time ....... It will not appear on tac,but yet heard, and slightly felt...... Nothing compared to cold LOP, not to bring that up..........Mostly in hot weather it is noticeable......

MAC

[ 07-17-2002: Message edited by: mackin ]</p>

[SID6FIVE]

IN REGARDS TO CRAFTY'S TRUCK,I LOOKED AT THE SCAN DATA PROVIDED-THE BALANCING RATE FOR HEALTHY INJECTORS IS PLUS OR MINUS 2.5MM.ANY HIGHER THAN THAT IS A SYMPTOM OF BAD INJECTORS-OF WHICH YOU HAVE SEVEN.I'VE SEEN THIS COUNTLESS TIMES(I'M IN MINNEAPOLIS MN)DUE TO THE LOUSY FUEL QUALITY IN THE MINWEST...SHOULD STILL BE COVERED BY WARRANTY,THOUGH...

[crafty]

With the data that was provided, GM powertrain told the dealership to replace the flywheel to solve my rough idle problem. It is being worked on as we speak. I should know by later this week if that was the cause of the problem. I have asked to see all parts etc so that I can tell everyone else what the problem may have been. Apparently I'm not the first one to have this happen and it always seems to show up at about 28,000 to 30,000 kms, just when mine did.
As for the idea of bad injectors, that was the techs first thought. If so, why does the roughness disappear as soon as you touch the throttle only a hair? Also, wouldn't you get some loss of power or smoking from the tailpipe? I have none of that. Both the tech and I had no real idea and I was surprised when the order to replace the flywheel came through. All of my fuel has come from a very busy truck stop that I've been using for almost 20 years so I'm very sure it's not bad fuel.
I will post more info once I talk to the dealer.

[ 07-29-2002: Message edited by: crafty ]

[ 07-29-2002: Message edited by: crafty ]</p>

[MEP]

I got my truck back from being serviced on Jul 12. The repair slip stated that the processor was recalibrated to the latest GM update. This is the first time that the truck had a software rev downloaded. The truck has been running great except one day last week, while in traffic w/AC on, the rough idle appeared again. The idle problem was excactly as before the software download. I continued on home and refused to think about the idle for the rest of the night. The next day the problem was gone and has not occured since but I know it will come back again.

Some history: The engine idles so rough the whole cab shakes! A car beside you at a stop light would notice the anntena shaking! It idles exactly like a 440 Chrysler I tuned up once where I forgot to connect the 4 plug wires on the RH bank then started it.

If you touch the gas pedal OR the truck is moving the idle smothes out to normal. How many accessories you hav running or if your foot is on the brake has no effect on the rough idle, only pressure on the accelerator or the vehicle moving makes the problem go away.

My truck is a manual box and I do not think the flywheel has anything to do w/this problem.

JB, member #739.

[crafty]

MEP,

I agree that it seems like the flywheel is a far out solution but that is what GM Powertrain said after reviewing the data that was sent to them. The service tech is only doing what they say. I agree 100% that the vibration will go away when the throttle is touched or you move in gear. For that reason I think it has nothing to do with the injectors or fuel system. The truck runs great otherwise. With any luck I will have the truck on the road tomorrow. The rough idle was showing up on average about once a week, sometimes twice so I should know if the new flywheel makes any difference pretty soon. This whole thing, including a rental car is being covered by GM so I'm not out much while they do this. I'll keep you posted as to what happens. :D :D :D

[MEP]

Crafty,
It was hot as hell in Boston today and my rough idle returned. My idle smooths out when I take my foot off the brake and the truck starts rolling. It does not have to be in gear.

GM might be on to something w/ the flywheel. When you touch the gas, the fuel rate to the injectors increases. When the vehicle starts rolling, the ECM may take this signal as an increase in load to the engine and respond to that by increasing the fuel rate. (like that vehicle surge you get when idling along in gear and loading down the engine, ie:touching the brake or turning a tight corner). When the engine speeds up slightly, this may cause a defective dual mass fly to go back into "balance". In my case, the hot weather may have some dramatic effect on the flywheel. When The mechanic down loaded the new ECM configuration, this slightly changed the idle characteristics of my engine, which probably changed the idle speed slightly.

[ 07-30-2002: Message edited by: MEP ]</p>

[letsgo]

crafty-- I thought all Canadian DURAMAX'S had ON-STAR If yours does you could have down loaded the engine fault with the operator while while sitting or driving in traffic, and had it forwarded to the GENERAL for analasis
At least thats what the book says
good luck.

GMC 2002 DURAMAX SLT EXCAB SHORT BOX 2500HD 4X4 AUTO.

[crafty]

MEP,
I'm supposed to be able to pick up the truck tonight after work, assuming everything works when they get it back together, so I will be asking to see the old flywheel etc to find out what was wrong with it. Seems to me I recall some discussion last fall about some trouble with the flywheels but I'm not sure.
As I said before, I doubt that the trouble is fuel related since all vibration disappears once the truck is in motion. I'm travelling to western Ontario this weekend so I should know how things are by the time I get back.

Letsgo,

Not all Dmaxes have ON Star. You only got it if you ordered an SLT and mine is an SLE. The tech was able to take a reading with the scan tool while it was running rough and that was where the posted info came from.

[crafty]

As promised, I was able to pick up the truck after work. The work order reads as follows:
Complaint: Rough Idle
Cause: Flywheel
Correction: Scan test - Call TAC - Install Updated Flywheel
Parts used, 1 flywheel
9 Bolts
2 Litres Fluid
4 Retainer
So far so good, no vibration so only time will tell. The mechanic is away on holidays so I can't ask him what exactly GM told him is wrong with the old flywheel. He returns on the 12th so I'll talk to him then. I'll keep you posted as to whether the vibration returns.
Boy it's nice to be back in the truck. That Sunfire made me feel like I was sitting on the ground ...and it had no POWER!!!!!! :D :D :D