i am working on a 1989 Volvo 780 with the 2.3l Turbo. my problem is that it will crank and attempt to fire, but it won't start, although sometimes it will run, but it runs rough and dies almost immediately. it it getting too much fuel and starving for air. i am suspecting either the idle air control valve or the coolant temp sensor.

any thoughts?

 

Do you mean the engine won't idle? Because not enough air is getting past the throttle plate? If so, have you cleaned the throttle plate? You can open the throttle plate with the setscrew and set the idle wherever you want if the idle motor /iac/what ever you want to call it is not opening.

Before idle control valves - the idle speed was set by the opening of the throttle plate. You can easily work around a non functional idle motor.

It's not your coolant temp sensor.