High idle

Tiny
CIVEY64
  • MEMBER
  • 1998 CHEVROLET TRUCK
  • 5.0L
  • 200,000 MILES
Truck constantly runs at around 1500-2000 rpm's. I have replaced the ICV as well as removed the throttle body and cleaned it. Still having the same issue. What do you suggest?
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Monday, February 22nd, 2016 AT 9:04 AM

3 Replies

Tiny
CARADIODOC
  • EXPERT
Check for a vacuum leak. Start by looking for dry-rotted or cracked vacuum hoses. Next, spray water over the engine while it is still cold and running to see if it gets sucked in anywhere, particularly around the intake manifold. You can also pinch off vacuum hoses to see if one brings the idle speed down. If you find one, work your way down that hose to where it branches apart, and do that on each branch.
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Monday, February 22nd, 2016 AT 9:37 AM
Tiny
CIVEY64
  • MEMBER
I have pinched the hose coming from the intake (about a three to four inch hose) I think and it bring down the idle tremendously, but I am by myself so I am not sure what the reading is. What is that indicating?
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Monday, February 22nd, 2016 AT 10:01 AM
Tiny
CARADIODOC
  • EXPERT
If idle speed drops when a hose is pinched, that is because you are blocking the leaking air from getting into the engine. Without knowing exactly which hose you are on, it is impossible to say if the lower engine speed is normal or if you are blocking a controlled and expected "leak". You typically do not get two, three, or four leaks all occur at once. You are looking for a single unintentional leak, as in a loose or cracked hose, or a leaking gasket. When you block that leak, engine speed will drop to normal; about 800 rpm's. If you are blocking a hose that is expected to have air flowing through it, engine speed likely won't drop all the way down to normal.

If blocking the hose you are on does bring engine speed down to where it should be, follow it to where another hose branches off, then pinch one of those to identify which one has the leak. Keep doing that to hopefully find the cause.
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Monday, February 22nd, 2016 AT 10:26 AM

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