Idles at 5000rpm

[IOWNJUNK]

Ok. Before I junk it, I'll ask here. 5.7/4l60. Truck shut off and wouldn't start. Fuel pressure 62 psi, had codes for crank and cam sensor, and no spark. Replaced cap, rotor and coil, IAC valve, cam sensor and now starts right up and revs to 5000rpm then dies. If I disconnect mass airflow sensor it starts then immediately revs to 5000rpm and stays there until I shut it off. No codes present now. Any other direction to go in would be appreciated. Thanks.

 

[BNielsen]

What engine and transmission?

 

[IOWNJUNK]

What engine and transmission?

****. Leave it to me to leave out the important parts....
5.7/4l60e

 

[BNielsen]

It could be the IAC valve being faulty? Do you still have the old one?

 

[IOWNJUNK]

It could be the IAC valve being faulty? Do you still have the old one?

I do, same results with both iac valves

 

[BNielsen]

I do, same results with both iac valves

Hm, maybe check the TPS? Is it a Vortec 5.7 or a TBI 5.7?

 

[618 Syndicate]

5000 rpm off the start sounds like a throttle linkage stuck.

 

[Caman96]

Broken or disconnected vacuum hose?

 

[Komet]

The problem in a general sense is the engine is getting a LOT more air than it should, so look for a problem with air entry.

 

[L31MaxExpress]

To get to 5,000 rpm is far more airflow than the IAC or a vacuum hose can move. The throttle is either hung open or the plenum exploded and cracked. Also could have had one of the rubber orings that seal the spider or plenum give out.