91 Lc Low Idle Problems, Low Idle Problems Options

[David K]

I've got a 91 LC that has about 188,000 mi on the 4.0 engine. In the past month it has begun to have a nasty engine shake that happens when the truck is idling. It usually sits around 900 - 1000 RPM's, and then when warm, it'll jump around between 500 - 800 rather erratically. The shake disappears when I increase the RPM's. Other than that and being gutless with 33" tires, the motor runs great.

I recently had the truck looked at before going to Mexico, and the technician said something about the timing chain being really loose and having adjusted the tensioner as much as he could. I know that timing chains wear and get loose with age, but would an old timing chain throw the timing off so much as to cause the truck to idle so rough? What are some other possibilities that are worth looking into?

Thanks for your help!

David

[FZJ Alaska]

I would consider folowing up with the part where the irratic idle begins with a warm engine. If the ECU is getting an unreliable temperature reading it will vary the timing accordingly. There are other condiderations of course, this is just a place to start.

[diagnostica]

CHECK YOUR IAC VALVE IF STICKING.

[Derrick]

Another quick fix would be just to up the idle speed to 1,000 or so.

[QUARTERS]

I have this same problem with my 1991 turbo diesel (auto) 80 Series, running rough between 600 - 800 rpm. I have replaced injectors, fuel pump, timing belt + tensioner, adjusted valve lifters..... with no success. Do diesels have an ECU? anymore suggestions??

Cheers