[bobstanster]

2004 Deville with 40k miles. Engine is idling and running rough , almost like a cylinder is not firing. Cleaned throttle body but no change . No codes . Any ideas ?

 

[Ranger]

Plugs?
Coil?
Partially stuck open EGR valve?
Vacuum leak?

 

[bobstanster]

Wouldn't there be a code

 

[Submariner409]

Depending - maybe, maybe not.

Spark and fuel delivery checks and diagnosis work.

 

[TheFlash]

with 40,000 miles on the garage queen when was the last time it was driven and then what happened?

 

[kaov]

Check the vacuum line coming out of the right (passenger) side of the intake manifold. If this line cracks it causes the engine to idle poorly. Due to the location it is difficult to see the crack. I found my leak by pushing in on the hose and closing up the leak, I could tell right away as the idle went back to normal immediately.