High idle

[boomdriver]

The open loop issue is no longer happening. I had a prom from a camaro in the ecm and I switched back to the original.

hmmm
Can't do that. Although the engines are almost the same,. the tuning is lots different.

As far as the throttle plate...vac cannot possibly hold it open unless the spring is missing. If there is nothing thats holding it open, like a bent linkage part or set screw, a build-up of oxidized aluminum can sometimes grow around where the butterfly normally seats. This might keep it cracked open. Get some fine emory cloth and try to polish the bore clean. Be certain to blow out any grit or debris afterwards. If you;re really adventurous, get yourself a dremmel,a sack of buff wheels, some brown tripoli jewelers rouge and about 2 days, and polish the bore of the TB to a mirror finish. That will prevent future corrosion and oxidation AND even aid in performance a hair...maybe a little. Looks nice if nothing else.
You can also polish up the butterfly and bevel the edges of the plate so it can't stick.
For now, clean the crud out of the spring and linkage, clean out the bore, and try it.

 

[tmkassin]

hmmm
Can't do that. Although the engines are almost the same,. the tuning is lots different.

As far as the throttle plate...vac cannot possibly hold it open unless the spring is missing. If there is nothing thats holding it open, like a bent linkage part or set screw, a build-up of oxidized aluminum can sometimes grow around where the butterfly normally seats. This might keep it cracked open. Get some fine emory cloth and try to polish the bore clean. Be certain to blow out any grit or debris afterwards. If you;re really adventurous, get yourself a dremmel,a sack of buff wheels, some brown tripoli jewelers rouge and about 2 days, and polish the bore of the TB to a mirror finish. That will prevent future corrosion and oxidation AND even aid in performance a hair...maybe a little. Looks nice if nothing else.
You can also polish up the butterfly and bevel the edges of the plate so it can't stick.
For now, clean the crud out of the spring and linkage, clean out the bore, and try it.

It is a newly rebuilt throttle body.

 

[boomdriver]

was'nt rebuilt right?

warranty claim?

 

[boomdriver]

does the throttle plate close completely when its disconnected from the cables? or only if you help it with your finger?
if it stays cracked open a hair no matter what, the rebuild may be defective.

While its all apart, check for the smooth operation of all the cables. if one is hanging up due to a broken wire strand, that can hold it open. But, if the cables are all off, then it has to be the throttle body itself, assuming everything else mechanically is ok.

 

[tmkassin]

Today I used a greenie pot scrubber and rubbed where the butterfly contacts the bore just to make sure it isn't binding. Then I lubed it with wd-40. After that I added a second spring to the throttle. It closes completely now but still idles high. Hooked up the scan tool, idle is 750. IAC is at 0? Vacuum leak? Now I'm back to square 1. Tomorrow I will retest all the vacuum circuits.

 

[ex-x-fire]

Is there a idle screw on the t-body? If so adjust it down, check the manual for minimum idle speed procedure . Sometimes the min. idle screw is capped off w/ a plug. Post some pics if you can.

 

[boomdriver]

I am not sure about the IAC measurement on yours, but on mine, if its too loose, and the pintle cannot travel far enough it will leak air and cause a high idle. Too much extended and the pintle gets damaged or bent when you screw the motor in the TB.

 

[G Winter]

With the engine not running check if there is any front to rear or vertical play. Any at all will cause the throttle plates to hang. I looked for high idle problem on my 90 for months before I discovered this. On mine if I would burp the throttle it would idle down some almost to normal.
You can not move the shaft with the engine running.

Glenn

 

[tmkassin]

Found the last ground terminal on the back of the motor today and cleaned it. It still refuses to idle down until I come to a complete stop. Hooked up the scan tool for the drive home. Left oxygen sensor jumps all over the place, from 120's to over 800. Very erratically. Bad sensor? Right sensor reads around mid 300's and fluxuates only a little bit. While I was under the car I noticed the plug for the 1st to 4th celenoid was unplugged and no skip shift eliminator. Can this cause any problems? Checked again for any vacuum leaks and there are NONE. I love my Vette!

 

[Schrade]

Hooked up the scan tool, idle is 750.

exxfire is in the neighborhood, but I think adjustment of the idle stop screw is the last thing to check, ESPECIALLY on a new TB. You haven't adjusted already, it have you? Some people do this to compensate for an undiagnosed problem, but that is not the right thing to do...

750 warmed up? STEADY 750???

IAC stepper count at 0 means the pintle is max'ed into the bypass port, and is blocking all air through the IAC controller. It's stuck with carbon fouling, OR, there's a vacuum leak (not likely, since you say it's steady when WARM), OR, ECM is sending a faulty signal, that's keeping IAC pegged, OR, ECM to IAC harness is shorted of open... Last possibility is the adjuster screw is too far extended, holding the butterfly open too far. Again, I think if you have NOT already adjusted this, it's probably where it is supposed to be :confused

Pull the IAC, work GENTLY the IAC pintle shaft. Feel for any 'grit' that's impeding the action. Spray in some THIN lube, and blow it through with compressed air, or a vacuum attachment, to pull the excess.

Re-install, and watch the stepper count on a scan.

If still at 0, pull it again, and test the IAC connector voltage, like so:

Block the IAC port with tape or something, making sure you see how you're blocking it - since this is what it's doing anyway, with a 0 count.

With it out, port blocked, get the spec IAC VOLTAGE at idle from FSM, and put your multimeter on the IAC connectors while it's idling. Look for variation as you work the throttle linkage.

If it dies show voltages at or near spec, connect the IAC to the connector (with the IAC port still blocked), and see if you get pintle movement while working the throttle linkage.

FSM test for IAC function, and voltages might be slightly different here...

 

[tmkassin]

exxfire is in the neighborhood, but I think adjustment of the idle stop screw is the last thing to check, ESPECIALLY on a new TB. You haven't adjusted already, it have you? Some people do this to compensate for an undiagnosed problem, but that is not the right thing to do...

750 warmed up? STEADY 750???

IAC stepper count at 0 means the pintle is max'ed into the bypass port, and is blocking all air through the IAC controller. It's stuck with carbon fouling, OR, there's a vacuum leak (not likely, since you say it's steady when WARM), OR, ECM is sending a faulty signal, that's keeping IAC pegged, OR, ECM to IAC harness is shorted of open... Last possibility is the adjuster screw is too far extended, holding the butterfly open too far. Again, I think if you have NOT already adjusted this, it's probably where it is supposed to be :confused

Pull the IAC, work GENTLY the IAC pintle shaft. Feel for any 'grit' that's impeding the action. Spray in some THIN lube, and blow it through with compressed air, or a vacuum attachment, to pull the excess.

Re-install, and watch the stepper count on a scan.

If still at 0, pull it again, and test the IAC connector voltage, like so:

Block the IAC port with tape or something, making sure you see how you're blocking it - since this is what it's doing anyway, with a 0 count.

With it out, port blocked, get the spec IAC VOLTAGE at idle from FSM, and put your multimeter on the IAC connectors while it's idling. Look for variation as you work the throttle linkage.

If it dies show voltages at or near spec, connect the IAC to the connector (with the IAC port still blocked), and see if you get pintle movement while working the throttle linkage.

FSM test for IAC function, and voltages might be slightly different here...

Using the scan tool I can see the IAC counts changing as it idles down. When I stop it is idleing around 1200 and the IAC steps down till the idle is around 650. But it will not do this till I am completely stopped. At that point the count is about 14 if I remember correctly. It is a new IAC in a brand new throttle body. The car runs flawlessly other than the idle issue.

 

[tmkassin]

New injectors, IAC, EGR, TPS, plugs, wires, MAP and a 52mm throttle body. Now today a left oxygen sensor. BINGO! it finally idles down. So I spent a little money trying to figure this out. And I was looking for any excuse to get the 52mm throttle body. It was still much cheaper than the dealership and I got a real education. The injectors were necessary too. This car runs fantastic now.

 

[shortej]

New injectors, IAC, EGR, TPS, plugs, wires, MAP and a 52mm throttle body. Now today a left oxygen sensor. BINGO! it finally idles down. So I spent a little money trying to figure this out. And I was looking for any excuse to get the 52mm throttle body. It was still much cheaper than the dealership and I got a real education. The injectors were necessary too. This car runs fantastic now.

Now just for clarification, when you say left side, is that drivers side or passinger side? The reason I ask is I have the same issue with with my 94 coupe, and I have replaced the drivers side already for a rich condition, the passinger O2 sensor code went away after I changed the drivers side. Wondering idf I need to change the passinger side as well? Thanks ES

 

[tmkassin]

I ended up replacing them both. It still idles about 1000 when cold and 750 when warmed up. Not the right numbers according to the FSM. I even re-set the min idle screw according to factory specs. It is way better than 1500 when cold and 900 when warmed up. I think it has to do with my airbox and exhaust mods.

 

[John Lupulio]

Hello

Nice car have high idle problem been through my 88 corvette my mechanic too its crazy idles 1300 disconnect mas air runs like have cam high performance connected mas air idles back up to high rpms everything is good car no leaks ecm new injectors 58mm throttle body air control motor no vacum leaks ect.....