Hello all,

I have a 94 ford lightning that revs at idle. Doesn't seem to do it until the engine warms. When stopped at a light i have to hold hard on the brakes or it wants to lunge forward.

I also noticed when i have the a/c on going down the highway it changes from defrost to vents. So i was curious if it is a vacuum line. I think i can hear it but i just can't find it. I was thinking it was under the upper intake manifold.

Any help would be nice.

Thanks in advanced
Stephen

 

Two things come to mind that you can try.
The first would be to get a piece of garden/vacuum hose about 3 ft long and with one end at your ear, probe the different areas to pick up the sound of the vacuum leak.
The other would be to pinch off just about every vacuum hose from the manifold taps and see which one provides the greatest difference and that should be your vacuum leak area.

 

Thank you i will give try. The pinching off of the hose might actually cuase more harm though. as these are some old vacuum line, and might be brittle. lol

 

Yes, you are absolutely correct, and that could possibly be one of the reasons for the possible vacuum leak.