1984 corvette idle problem - PART 2
Thread Starter
Heel & Toe
Joined: Apr 2011
Posts: 22
Likes: 0
1984 corvette idle problem - PART 2
Hello again,
I am still having trouble lowering my idle speed on my 84 vette. I tried the procedure to set the TBI settings, grounded the ALDL to set the IACs, set the TPS.....still runs about 900-1100 at idle and engine hot. When I remove the PCV valve and plug the vacuum port, the idle drops to 700-800. Thats where it should be - right? Any suggestions about what else to check or test. Feel free to be as technical as you want - I can understand it - THANK YOU
I am still having trouble lowering my idle speed on my 84 vette. I tried the procedure to set the TBI settings, grounded the ALDL to set the IACs, set the TPS.....still runs about 900-1100 at idle and engine hot. When I remove the PCV valve and plug the vacuum port, the idle drops to 700-800. Thats where it should be - right? Any suggestions about what else to check or test. Feel free to be as technical as you want - I can understand it - THANK YOU
Racer
Joined: Nov 2010
Posts: 460
Likes: 1
From: Oliphant Ontario
Sounds like you have a vacuum leak somewhere since plugging the PVC reduces the amount of air going in. A vacuum leak can allow enough air that the IAC can't close down enough to limit idle speed..
That said, what are you basing your idle RPM on? On my 87 slash 90, I was trying in vain to lower my idle.... until I finally got datamaster working right and found out my tach reads over 200rpm high.
That said, what are you basing your idle RPM on? On my 87 slash 90, I was trying in vain to lower my idle.... until I finally got datamaster working right and found out my tach reads over 200rpm high.
Racer
Joined: Nov 2010
Posts: 460
Likes: 1
From: Oliphant Ontario
On mine they seemed to be everywhere 
Main ones were intake manifold to plenum was loose on passenger side, tubes to base was leaking at #5 and #7. PVC and line to brakes, hard and leaking around nipples. EGR grossly gummed up and not closing fully (this will usually cause rough idle more than high)..
Also if the IAC is defective, wrong or sticking it won't close all the way.
Sorry, just noticed your an 84, don't know much about the cross ram engines......
Main ones were intake manifold to plenum was loose on passenger side, tubes to base was leaking at #5 and #7. PVC and line to brakes, hard and leaking around nipples. EGR grossly gummed up and not closing fully (this will usually cause rough idle more than high)..
Also if the IAC is defective, wrong or sticking it won't close all the way.
Sorry, just noticed your an 84, don't know much about the cross ram engines......
Thread Starter
Heel & Toe
Joined: Apr 2011
Posts: 22
Likes: 0
i checked the IACs. I removed them and cleaned them and adjusted them to close the port. I know they are closed because I can spray carb cleaner into the IAC ports and it does not change RPMs. They are shut tight. I just am trying to locate a "common" place to check before pulling off the plenum and intake....
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Pro
Joined: Jul 2002
Posts: 703
Likes: 0
From: Milwaukee Wi
did you close down the butterflies with the set screw?
Melting Slicks
Joined: May 2010
Posts: 2,082
Likes: 3
From: Conowingo Maryland
These throdle bodies are well know for coming loose and blown gaskets. Take a socket and try to tighten them down if they are loose. It is a 2 min check and you may be surprised at what you find.
