Idle swing!

I have a 94 Transport with a major problem of the idle swinging so bad the engine dies. I have taken it to 3 repair shops and none can fix it. It only does it when cold, after the engine gets past 160' it runs great. New parts include egr valve, idle air motor, o2 sensor, plugs and wires, coolent temp sensor, cam sensor, crank sensor and
upper intake gasket. Any ideas would help. Thanks

 

[ivymike]

I'd start with detailed diagrams of the IAC and EGR systems (try a shop manual, perhaps available at

http://www.helminc.com).

It sounded to me like you were on the right track with the coolant temp sensor and the idle air control motor. What other components are in the idle air control system on that vehicle? Is there more than one IAC valve? Is the IAC valve getting an appropriate signal from whatever controls it (test with multimeter)?

Alternatively, is there a temperature measurement device in the EGR control system?

 

[TheBlacksmith]

Not sure if this applies, but is the intake manifold straight and torqued properly. Had a lot of engines where the manifold was aluminum two piece and torqued to 140 IN-LBS max. People would overtighten it, warp it and the surfaces needed a skim cut to get a good seal. Also, are the throttle plates set properly? Some people try to adjust or correct idle speed by closing the throttle plates a little, then there is not enough airflow and the IAC valve opens fully without affecting the speed enough. Once the engine is warm, the IAC (just barely) has enough travel.

Blacksmith