My idle is around 900-1000 in park and 800 in gear. I replaced the intake gaskets and the tbi gaskets. The car idles smooth and runs good. I've checked for vacumm leaks and couldn't really find any. Is it correct that the computer sets the idle ? Is it anything besides a vacumm leak that could be causing this. It runs o.k., I just don't like the hard shift into gear or the wanting to surg ahead when your stopped.

 

The computer sets the idle speed based on information given by several engine sensors. The idle speed is changed via the IAC (Idle Air Control) motors. Perhaps one or both are gummed up or weak. Check the Computer (ECM) for error codes. As you know, a vacuum leak can cause a high idle, perhaps too high for the ECM to correct.

 

After changing gaskets, you need to balance your TBs at 6" WC and set the base idle at 525 rpm using the throttle-stop screw on the driver's side TB. The computer works from there to fine tune the idle with the IACs. If you need instructions on this, search the Corvette Fever website and/or Crossfire Injection Forum.

If you've already done all this, I'd look for a hidden vacuum leak.

Peter

 

You may or may not need to balance the TBI's. The air /gas mixture is very sensitive. First see if the the caps on the TBI's to access the adjustment screws are out. Previous owners sometime mess with the balancing to adjust for a gasket leak. If this was done before then yes you do need to balance them.

The TBi's come balanced from the factory adjusting them is a bandaid solution for other vaccum leaks. So if you caps are there don't adjust. the cause is something else.

I assume you unplugged the IAC's to get at the gasket. You realize the IAC's will not reset until you go for a drive at about 35 mph for about 5 miles. Your idle will be higher until you do so.

Did you plug all the hoses back in? Including the one that goes to the air cleaner?

Look for other causes. Is the EGR solenoid okay? No leak?

Not the idle adjustment screw on the front TBI. It comes welded to the shaft from the factory. Is the weld grinded off? If so someone has probably played with it. So if the caps are on and that weld is broken its probably been tampered with. Back it off a 1/4 turn at a time until you get the idle down to about 600.

If the caps are there and the weld is there. No other apparent problem. I would grind the weld off and start with backing off on the idle screw. Remember your starting point incase that isn't the cause.

Did you move the TPS? It needs to be set at .525 volts.

Lastly, how are the throttle shafts? Do you have play in them? Could be a cause of a vaccum leak.

Jim

 

Jim is correct. We have both tuned our cars. Check out this link it will tell you how to do it correctly.

http://www.corvettefever.com/techart...ing/index.html

Also, try replacing the coolant temp sensor (not expensive $30) in the front of the engine above the waterpump. I replaced mine and it made a world of differance. My car Idles at 750 in park and 650 in gear which is a little fast but the car seems to like it there and it idles relatively smooth. I also advanced my timing a little 10 degrees btdc.

 

If it were me, I'd check the TPS setting as suggested by Jim because the ECM has to know where the TB plates are to make accurate calculations. .525v is the correct setting. Next is to check the TB shafts for play...also suggested. If they move at all, they are worn and need to be bushed...PERIOD! Some say they only move a little and thats ok...NOT! A little is too much and means they are leaking to atmoshpere or a vacuum leak. If the shafts are leaking it makes it impossible to balance the TBs correctly becaue when you set it perfect and move the throttle, the setting is now off again because of the (small) play in the shafts. you will be chasing your tail around and around on that one and get nowhere.

You don't need to rebalance or balance the TBs if you replace the manifold gaskets unless of course you suspect that someone else has tappered with the balance or you did for some reason.

The IACs also like Jim as mentioned be be another reason IMO. So recheck everything and post your results.

 

Wow, where to start. First, the car has been drivin about a 1000ml. since the gasket change. All the hoses are on, even the one under the air cleaner and none seem to leak. The plugs are out, so I assume the previous owner screwed with them to compinsate for the bad gasket. I will start there and keep you posted. Oh, EGR is o.k..

 

"Bump"...any news yet?