Hi Idle

[scottskill]

Help, I have a dilemma! Just finished porting the intake system not including the cylinder head, recalls the chip,headers, and unfortunately cleaned the throttle body! At this point in time I'm having Hi idle problems, 2k rpm start up lowering to 1100/1500 rpm. Placed cardboard in front of airhorn while engine running and continues to run @ Hi idle. Used propane around the vacuum fittings, gasket mating areas,injectors with no increase in Hi idle rpm. My question is what steps shall I try to accomplish next to get this idle corrected?

[We Gone]

Go back and recheck all your work, I'll bet its a vacuum issue, double check all the lines.

[Paul Workman]

Go back and recheck all your work, I'll bet its a vacuum issue, double check all the lines.

Vacuum for sure! No/little change w/ a piece of cardboard blocking the air horn?

the brake booster hose?
the PVC line to the plenum and the
the purge vacuum line next to it?
the HVAC line or SPT line(s) - one on either side of the center plenum
the vacuum line (90s) under the plenum on the air horn
check the fuel pressure regulator hose @ back of the plenum
PVC housing and hoses (back of plenum)
secondary port throttle vacuum

And, then there's the plenum gaskets, IH gaskets and the Throttle Body gaskets...

Any of the above. (In RED are some that caused the problem on mine, specifically.)

[XfireZ51]

Help, I have a dilemma! Just finished porting the intake system not including the cylinder head, recalls the chip,headers, and unfortunately cleaned the throttle body! At this point in time I'm having Hi idle problems, 2k rpm start up lowering to 1100/1500 rpm. Placed cardboard in front of airhorn while engine running and continues to run @ Hi idle. Used propane around the vacuum fittings, gasket mating areas,injectors with no increase in Hi idle rpm. My question is what steps shall I try to accomplish next to get this idle corrected?

I'm assuming you disconnected the throttle cable and removed the IAC motor.
The Min Air adjustment at idle of the throttle blades may be required. Also a reset of the IAC motor if it was removed from the throttle body. That's a good place to start.

[scottskill]

Yes I removed the IAC, however I can't find a thread on how to reset the IAC? Also the thread for throttle blade clearance?

[Racinfan83]

MAP sensor hose connection at rear of plenum was leaking causing my high idle issue....

[Billy Mild]

Sounds like a vacuum leak more so then a throttle blade issue.

Do you have a mityvac to test with?

[XfireZ51]

Sounds like a vacuum leak more so then a throttle blade issue.

Do you have a mityvac to test with?

Min Air adjustment IS a vacuum leak.

[Billy Mild]

Min Air adjustment IS a vacuum leak.

I'm talking about a vacuum hose, not a throttlebody issue. If he used a piece of cardboard to cover the airhorn and the idle was still high that points to a vacuum leak AFTER the throttle blades.

[scottskill]

Yes, I have a mityvac. Next step isolate each vacuum line independently.

[XfireZ51]

I'm talking about a vacuum hose, not a throttlebody issue. If he used a piece of cardboard to cover the airhorn and the idle was still high that points to a vacuum leak AFTER the throttle blades.

And I was simply pointing out that throttle plate openings are, technically speaking, vacuum leaks. IACs create regulated vacuum leaks also.

[scottskill]

Accomplished the task of isolating each vacuum line independently and found several joint connection blocks leaking. Repaired the connections with silicone, no leaks noted. Reassembled intake runs like a LT5 should with 19 inches of vacuum! Thanks guys for the help!

[Billy Mild]

Accomplished the task of isolating each vacuum line independently and found several joint connection blocks leaking. Repaired the connections with silicone, no leaks noted. Reassembled intake runs like a LT5 should with 19 inches of vacuum! Thanks guys for the help!

Did you replace the rubber connections with Silicone hose?

[scottskill]

No, applied silicone to the hard line after cleaning then inserted to the end coupling let it semi cure reinstalled.

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