# 1990 d21 HB rough idle after warm- yes i searched



## joeysmurf (Oct 24, 2007)

I am new here and have run into the most frustrating issue. My truck, with 130k that i have put on it since new, has been sitting for about 4 years. I got it running the other day and seemed to be okay. I changed all fluids, twice, have run 3 tanks of fuel through her, and changed the coil, wires, plugs, rotor, and cap. I also replaced thermostat. It seems to be fine, maybe a little tired but runs pretty darn good. Then this issue. Once warm the engine while idle will start to run rough, you can hear the idler catching it and a large amount of air being sucked through the throttle body. Most of the time the idler catches it and it will idle again fine, then rough and stall. When it is about to stall if you give it gas, it boggs down badly. Then you feather it and it will catch. Now if you yo yo the throttle while sitting in traffic it will be fine, no issue. I have tried to run the self diagnostic on the ecu and no codes show. The only down side is when i set the ecu into function 3, self diagnosis, i set the idle to high, but have solved that. Then i replaced all the vacum hoses around the EGR, and it feels as if it moves fine under vacum. 

So in summary, the truck does fine idling until the engine is warm and then it starts to rough idle. Which is a pain because if you do not yo yo the throtle it will shut off in traffic, then very hard to restart.

please help!

joey


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## scout (Aug 24, 2007)

So in summary, the truck does fine idling until the engine is warm and then it starts to rough idle. Which is a pain because if you do not yo yo the throtle it will shut off in traffic, then very hard to restart.

I don't know anything about the 90 specifically but it sounds like the extra fuel needed during a cold start is not being terminated after operating temp is reached. By yo-yoing the the throttle you are increasing the engine speed and it is able to absorb the extra fuel with the higher rpm. 
Hope that is of some help.


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## joeysmurf (Oct 24, 2007)

Thanks Scout, I had never thought of it as a fuel supply issue. I, assumed, and i do mean assumed, that the flow of gas to the rail was constant, so no matter hot or cold it never changed. However the other sensors, EgR, IAC, MAT, all changed based on the engine temp, and not the fuel. It seems though to be lack of air as you stated, just never thought of it as too much gas. 

The really wierd part is when i say engine warm, does not mean every time. But as an example, drove for 30 minutes in very tight stop and go crappy ass traffic. It did very very good, no isssue, no blip of throttle, no yo yo, then it started. As the light changed i tried to give her the juice, and she crapped out. So frantically i tried to start back, 3 times it finnaly hit, and boom i was gone. Then next light, same thing she wanted to die, so this time i made sure she stayed above idle and yo yo the whole way home while sitting still. 

joey


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## veesix (Jul 18, 2004)

Did you notice the exhaust, when the engine started to struggle?

Black exhaust means the mixture is rich. It's a suprise that there are no error codes.


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## joeysmurf (Oct 24, 2007)

No Black Smoke noticed. I did however, with the help of some others, remove the old O2 sensor and retap and replace with a new one. This seemed to have helped the over all running, smoothness, of the engine, but sadly did nothing for the idle issue once warm. 

The next thing that was suggested was to look at the injecters. I have run cleaner through the tank twice, but due to the time it sat, may need a more robust job on them. Again we looked at the EGR, did not replace, and inspected all hoses. So going to look at fuel dilivery next. One suggestion is a flooding of one of the injectors. I really do not think it is a clog issue because there is not hesitation under accel. 

I will post findings.

thanks 

joey


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## joeysmurf (Oct 24, 2007)

as an update... pulled all plugs for visual inspection. All plugs (less than 3 weeks old) look good, they appeared same in coloration, nothing obviously different between them. So injectors appear to have same behavior. 


Friend of mine found this

“
Section:
Engine Mechanical

Reference:
Technical Bulletin NTB95-017

Date:
February 8, 1995

ENGINE OIL LEVEL AND GRADE

APPLIED VEHICLES:
All

SERVICE INFORMATION

The cause of some driveability incidents is incorrect oil level or
viscosity. Whenever you evaluate a vehicle for a driveability problem,
check the oil level first. (It is a good practice to check oil level on
every vehicle that you work on.)

 Overfilling may cause engine vibration or valve train clatter on vehicles
with hydraulic lash adjusters due to oil aeration when the crankshaft hits
the oil. Using the wrong viscosity oil can cause rough or low idle
resulting from improper operation of the hydraulic lash adjusters.

When you add or change the engine oil, follow the service manual
recommendations regarding proper oil fill level. Do not overfill the
crankcase. If you find a vehicle to be overfilled with oil, drain the
excess oil and dispose of properly. Remember to wait ten (10) minutes
after refilling before checking. This allows time for the oil to drain
back to the pan.

Always use the proper viscosity oil specified by the service manual for
the temperature range in your geographic area. The viscosity
specifications ensure proper engine operation and best engine efficiency.”

........

I found the oil to be over filled by half a qrt or so. Removed oil until measured amount is between low and high on the stick. Motor stumbled at light on way to work this morning but it caught itself at light. Will post more as it happens…

Please if you can help..


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## joeysmurf (Oct 24, 2007)

So a couple of days have passed and no changes to report, except i broke the centershaft bearing, and that is a very bad noise for those of who have not experienced it before. 

So still at a lost on the idle issue. 

I also here what i think is timining change slap, noise, coming from the engine. So i may have to pull the front cover soon and replace that. 

joey


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