John

 The problem is most likely related to the Idle Stabilizer Valve (ISV) circuit.
The stabilizer valve operates when the engine is cold to keep the engine from
dying. Once the engine is warm, and the ECU gets a "warm" signal from the Temp
II sensor, the idle stabilizer is isolated from the circuit. The engine should
idle smoothly at that point.

Try removing and cleaning it with some carb cleaner. Also remove and reseat the
Idle Stabilizer Control ( a box located behind the right tail-light - remove
the light housing to get to it). This action will help by removing any slight
corrosion that may have occured over time.

The ISV should hum and you should feel a slight vibration when it is operating.

John Rodgers
88 GL Driver

john Runberg wrote:

> Can anyone help me diagnose this?
>
> When I start my 90 bus in the morning it wants to run really rough - no
> power, hesitates, etc... Exhaust seems to have moisture in it and it leaves
> a slight damp mark on the pavement. If I let it idle for a few minutes it
> runs OK (after the OX sensor has kicked in?). Once it's moving it runs
> great. If I start it in the afternoon it doesn't seem to exhibit the same
> behavior. Odd.
>