Ok I swaped a 95 lt1 into a 87 fire bird, and everything is great exept when I start the car the idle is fine around 750 or so and then about a minute later or as sone as I give it some gas the idle jumps up to about 1000 rpm. Any ideas what could cause this?

If it is true that the oxygen sensors do not work untill they hit about 600 degrees it cant be them because the car never got that hot. I only ran it 30 seconds or so at a time.

PCMforless did my tune so I do not think it is that!

could it be?
iac valve adjustment?
tps sensor?
oxygen sensors?

ANY IDEAS?

 

Do you have all of the air inlet pieces hooked up? MAF plugged in? They should idle at around 850 stock. Mine idled up high when I didn't have any of the air inlet hoses hooked up and a bare TB. The O2's are heated in the LT1's so that isn't really a problem, however until the car gets to around 190* it stays in open loop instead of closed but the idle is usually the same.

 

The air intake is hooked up. Could it be that the computer just needs time to learn the idle with all of the new components? The longest that it has run so far was untill the second fan kicks on. And the batery is aways being disconnected.

 

The computer learning doesn't have anything to do with the idle. I can unhook the battery, come back hours later hook it back up, start it up and it will idle at 1k for about 30 seconds, then drop to 850 like it should. I would say you have a vacuum port off as well maybe, that will make it idle higher, or a vacuum leak.

 

I spend hours today going over the car and found nothing.

-No vacuum leak checked with starting fluid!
-Checked: MAF,IAT,TPS,MAP: all seemed fine with a multimeter!
-Tried to check oxygen sensors not sure about results, I also unpluged the oxygen sensors and it still idled high?
-Unplugged the ignition and ran off stock opti, with same results!

When I start the car the idle is about 800 or so for about a minute or two,or when I pump the throttle the idle goes to around 1000-1200!

The car seemed to idle great with open headers and no alternator (I think),then I put them on and the idle went high.

ANY IDEAS?
THANKS

 

Do you have the hose hooked up that goes around to the bottom of the TB? I was beating my brains out trying to figure why mine was idling high until someone asked me if it was hooked up. It is the one that goes around to the PCV valve.

 

Ya everything is hooked up!

I am out of ideas!

Do you think that I sould just adjust the iac valve or throttle stop bolt?

 

I don't think you can adjust the iac, it's bolted on solid with no adjustment.

 

Today I went over all of the sensors again, and bench tested the oxygen sensors, every sensor reads fine. I replaced the coolant temperature sensor because I thought it was bad, but it was not! I also sprayed more carb-choke cleaner, and found no vacuum leaks. When the engine goes into closed loop the idle jumps to 1000-1200 rpm. There is also no check engine light on, but it comes on when I unplug a sensor, does that mean that all of the sensors are fine?

Any ideas????
(this is making me crazzzzy)

 

One thing I did think of....look at the end of the TB and see if the plug has been taken out to gain access to the set screw. If it has been, someone may have turned it in raising the idle up.

 

Its a brand new holley throttle body, and it is set the way that it came. I am thinking that it has to be a sensor because it only happens in closed loop, But it is not throwing the service engine soon light?

Thanks Klortho for all of your help and any ideas that might still think of.