High Idle Issue

[Hammer]

I have had a high idle issue for about a week now. Last weekend I started the Beast and it didn't quite catch, ended with what could be called a backfire, but it was very small. Since then I have searched the forums for anything I could find and it appears a vaccum leak is imminent. I have replaced the common problem, the PCV connector (it needed it) but can't seem to see anything else loose or hissing that would cause this.
I start it and it will idle high at about 2000 RPM and slowly reduce to around 1000.

What else could be causing this issue? Does the Plenum need to come off?

Thanks

[WB9MCW]

Have you determined if your vac pump is constant on this would indicate a leak and pull to investigate further--sorry to say if that is the case.

lets see what the others say!

[A26B]

I'm assuming you've already checked the MAP sensor hose which is notorious for blowing off during one of those start/backfire events.

[Hammer]

I'm assuming you've already checked the MAP sensor hose which is notorious for blowing off during one of those start/backfire events.

That's what it is Jerry. I can see it blown off. I am going to atempt to get it back on without pulling the plenum. I'll post in a bit. Thanks

[Hammer]

Well I got the :cry: Map Sensor:cry: fuel evap system hose back on without pulling the plenum. I removed the aluminum cover over the throttle mechanism and then the fuel injector connection. This gives room to get a coat hanger in there and pull the hose on. There is what appears to be a metal ring around the hose. if you make a loop at the end of the coat hanger and bend it just right it's pretty easy (and ingenious I might add) to get it on. :-D
High idle fixed.

[Jeffvette]

Have you determined if your vac pump is constant on this would indicate a leak and pull to investigate further--sorry to say if that is the case.

lets see what the others say!

Vacuum pump would not run if vacuum leak is present in the manifold. It's only concerns are holding the secondary system at a 12" minimum.

John and you can slide your hand back behind the motor and grab a hold of the map sensor hose and connection with out removing anything. just make sure the motor is cool.

[Jeffvette]

Well I got the Map Sensor hose back on without pulling the plenum. I removed the aluminum cover over the throttle mechanism and then the fuel injector connection. This gives room to get a coat hanger in there and pull the hose on. There is what appears to be a metal ring around the hose. if you make a loop at the end of the coat hanger and bend it just right it's pretty easy (and ingenious I might add) to get it on. :-D
High idle fixed.

That hose is not for the map sensor. It's for the fuel evap system (if you are talking about the one that goes back under the front of the plenum.)

[Hammer]

That hose is not for the map sensor. It's for the fuel evap system (if you are talking about the one that goes back under the front of the plenum.)

Thanks, that's the one. I think they must have put that little ridge around that hose for a reason. :handshak:

I am still a virgin. Time will come soon. You and Rob will know cause the stuff'l (Plenum and Injector Hsings) come your way.

[WB9MCW]

So a fuel evap hose can cause high idle too? Two hoses that can come off and cause high idle--

who would have thunk it?

thnx for the correction Jeff--that is why I told him to wait to see what others had to say.

What would be another symptom of seconday system below 12" besides the constant vac pump running? Any performance issues if a leak in the secondary system?

[Jeffvette]

A small leak in the secondary system (pump cycling with the key in the on position and motor not running) will not cause any other symptoms. The engine provides the initial vacuum for the system and when the car is running the pump will be silent. If the leak is large enough the pump will come on when the secondary system is in use and it drops. The pump will come on and hold vacuum at 12".

[cuisinartvette]

Is it normal for the pump to come on at all with the motor off and the key in "ON" position, should you never hear it?

[1990 quasar blue]

Is it normal for the pump to come on at all with the motor off and the key in "ON" position, should you never hear it?

About two years ago mine would give a quick blip (fraction of a second) every minute or so. I pulled the plenum and replaced the spider assembly. After that it would run once when the key was first turned on and then be silent. I stopped timing it after twenty minutes. Now it's back down to every two minutes again. If you have a leak just get a vacuum gauge and pull the plenum. It's pretty easy to track it down.
http://www.corvetteactioncenter.com/forums/showthread.php?threadid=14272

[cuisinartvette]

Cool...Sounds like I may have a slight leak..
I get a quick blip every few seconds before I turn it on. Runs good though..
Good excuse to port I guess.