89 348ts, how to adjust idle

I don't believe there is an actual "idle speed screw" on a 348 for simple adjustment. The idle speed is controlled by the Motronic ECU, through the idle stabilizer units. If the system is working correctly, and no one has messed with it, you should always have a steady idle around 950rpm.

There are numerous situations which could cause the idle to run higher than normal. If you have had the battery disconnected recently, or the battery has run down, you could start by "re-initializing" the Motronics. You should check for vacuum leaks due to loose clamps, or deteriorating rubber boots. If someone has messed with the throttle synchro linkage, you may have an imbalance between the two banks. You could have something as simple as a badly adjusted or sticking throttle cable, or even a floor mat under the pedal that is preventing the pedal from returning fully to rest.

Check the simple things first!

 

Not sure if you know or not, but these cars idle around 950-1000 RPM.

You dont have your floor mat wedged under the gas pedal do you?

Perhaps you have a sticking throttle cable?

More info please.