C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Crazy idle almost tuned

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Old Jan 29, 2015 | 04:15 PM
  #21  
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Originally Posted by chevyowner
Not entirely sure. It will be blue and black, or blue and grey. They will just change resistance in different directions.
Re check now you was right.. Right couple blu/grey either blu/black,
Blu always need to be is signal to computer

Well test result is from 2.68 k ohm to 7.61 k ohm

Could works properly? Or its a bad TPS sympthom

http://www.ehow.com/how_5832553_chec...on-sensor.html

Some instructions here
They say any sudden drops or increase in the reading indicates a bad tps

Its hard to say

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Old Jan 29, 2015 | 11:11 PM
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The one I have ranges from 2.8k-7kohms the throttle body is not on anything.

PS
Have you checked the IAC?
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Old Jan 30, 2015 | 05:54 AM
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Originally Posted by chevyowner
The one I have ranges from 2.8k-7kohms the throttle body is not on anything.

PS
Have you checked the IAC?
IAC is new, just Replaced, possible to do a multimeter test on IAC wiring?
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Old Jan 30, 2015 | 10:32 AM
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Yes you can ohm test the IAC, but I don't have any links for it.
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Old Jan 30, 2015 | 07:04 PM
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Originally Posted by chevyowner
Yes you can ohm test the IAC, but I don't have any links for it.
i've re-tested TPS with omh scale, slowly rotating the shaft, and i've got a good response in omh scale, the slowest movement the slowest increase in reading, no sudden drop or rise, so TPS shuold properly works,

Also Tested the IAC wiring is very simply, 4 connectors two external 0.35V two internal 11.55V, So think IAC is working properly too

probabily the issue is about IAC count, how said from Bjankusky, but i've no scanner and no tuning program

DAMN IT

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Old Feb 7, 2016 | 03:39 PM
  #26  
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Default could be here the problem

Last contact between screw and TB shaft occur at 0,61 v at TPS, unscrew again and TB shaft doesn't follow screw. It stay there.

Supposed to be ok?? Seems not be stucked

I have not datamaster or any other scantool unfortunately yet
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Old Feb 7, 2016 | 04:27 PM
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Originally Posted by Christi@n
Last contact between screw and TB shaft occur at 0,61 v at TPS, unscrew again and TB shaft doesn't follow screw. It stay there.

Supposed to be ok?? Seems not be stucked

I have not datamaster or any other scantool unfortunately yet
That simply means that the butterflies in the opening of the TB have closed completely and you cannot go back from there. It also means that any air going to the motor comes from one of two places. The "metered air leak" aka IAC or an unmetered air leak which is the leak from a broken hose, leaking gasket, etc.

Without a scantool, there is no way to see what is going on. So if you have a high idle, it could be that there is a leaking gasket or hose which allows unmetered air into the engine. For instance, if the TB is in the position you mentioned and the IAC counts are 0, it means the engine is getting too much air. Usually that signifies a leak from a hose or gasket.

On my L98, I get everything hot and running and the temps stabilized. Shut everything but the motor off and see what the IAC counts are. If it is more than 20, it means the engine is not having enough air and the IAC is being commanded to open up more. In which case, you have to turn the screw in to get the throttle plates or butterfly to open up more. Rev it and recheck. If it is less than 20 and the TB is in the current state you mentioned, it means too much air is coming in and the IAC is unable to shut down the air leak enough. At which point, you go hunting for the leak.

PS. I forget which year is the bastard year where it is between OBD1 and OBD2 and some have had difficulties reading the ECM except with a Tech 1 or a Snap On scanner. Someone else will chime in. Regardless, you need a scanner to do anything. This is not the carb style where you can simply throw parts and get it working. You need to understand more about the car and have a scanner.

Last edited by aklim; Feb 7, 2016 at 04:29 PM.
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Old Feb 8, 2016 | 05:54 AM
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Originally Posted by aklim

PS. I forget which year is the bastard year where it is between OBD1 and OBD2 and some have had difficulties reading the ECM except with a Tech 1 or a Snap On scanner. Someone else will chime in. Regardless, you need a scanner to do anything. This is not the carb style where you can simply throw parts and get it working. You need to understand more about the car and have a scanner.
that bastard year is my year (1995) i have OBD 2 plug coupled with OBD 1 software,
So i would assume taht the only thing i can get is tuner cat datamaster


My idle is not so high, but it won't go under 900 rpm, in place of 750 rpm.

Last edited by Christi@n; Feb 8, 2016 at 05:56 AM.
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Old Feb 8, 2016 | 10:04 AM
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Originally Posted by Christi@n
that bastard year is my year (1995) i have OBD 2 plug coupled with OBD 1 software,
So i would assume taht the only thing i can get is tuner cat datamaster


My idle is not so high, but it won't go under 900 rpm, in place of 750 rpm.
That or Tech 1? I would think that a Snap On scanner might work. Ask around. I have an older "The Brick" that I bought off ebay. I have a 91 so IDK.

Without data, we can guess all day long but I don't know how you know you have 900 RPM. I really don't trust the tach you have in the car. I prefer to see what the ECM says because my tach was over 300 RPM faster than it should be. On my F-body the tach was spot on but on the Vettes, I haven't read much that says they are accurate. Mine is reasonably accurate now that I have sent it in for calibration. I verify RPM with my timing light that has a tach and the scanner readout. I only use the stock tach for when I am driving.
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Old Feb 8, 2016 | 10:20 AM
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Originally Posted by aklim

Without data, we can guess all day long .
Yes... I had to take something has soon as possible or dataster or scanner
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Old Feb 8, 2016 | 10:22 AM
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Originally Posted by aklim
That or Tech 1? I would think that a Snap On scanner might work. Ask around. I have an older "The Brick" that I bought off ebay. I have a 91 so IDK.

Without data, we can guess all day long but I don't know how you know you have 900 RPM. I really don't trust the tach you have in the car. I prefer to see what the ECM says.
Yes from tach
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Old Feb 8, 2016 | 10:23 AM
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Originally Posted by Christi@n
Yes from tach
I wouldn't trust it until I get a scanner of some sort. Can you check whether the scanner at Autozone can help?
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Old Feb 8, 2016 | 10:26 AM
  #33  
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I've already seen a lot of scanner around, and I've definetly decided for tunercar data master, that is a more complete platform.

Just I had to wait a little, due I havent't 200$ to spent at the moment
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Old Feb 8, 2016 | 10:41 AM
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Originally Posted by Christi@n
Yes... I had to take something has soon as possible or dataster or scanner
If the Autozone one will work, check out IAC counts when you are there with ONLY engine running. Also check out the Ambient air temp and the engine temp so you can see if the values are plausible. So if it says your ambient air temp is 20 degrees and it is 75, you have a problem. If it says your IAC count is 0, you also might have an air leak since you backed it all the way close.

Not sure how to do this with MAF but with SD I take off the hose going to the TB if the counts are 0 and plug off the IAC physically and see if it changes. If the engine still runs, there is definitely an air leak.
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Old Feb 8, 2016 | 10:42 AM
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Originally Posted by Christi@n
I've already seen a lot of scanner around, and I've definetly decided for tunercar data master, that is a more complete platform.

Just I had to wait a little, due I havent't 200$ to spent at the moment
I bought the cord and downloaded the free system since I am not going to tune my own car ever.
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Old Feb 8, 2016 | 10:57 AM
  #36  
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Originally Posted by DanielRicany
That's not the proper way to adjust the idle. You need to do an idle reset procedure. The ECM controls the idle not you at the throttle body. You're forcing a higher idle than what it should be.
Get the screw back to where it was.

Originally Posted by Christi@n
I'm close to properly tune my lt1 1995 idle.

At this moment idle at 900 rmp, if car is stopped in neutral (man trans),
Obtained by idle regulation screw on TB

The Only one issue remain is on running

As instance: go 3rd engine 900 rpm, step on clutch and go neutral for a while idle doesn't come back to 900 rpm, but stay up, about 1100-1200 rpm,
Until car is stopped Again, then slowly come back to 900 rpm


Any idea? Seems like to be something related to the speed.

ASR cable, speed sensor on transmission?
Already check for vacuum leaks seems not to be, even since that if idle works properly with car stopped should works properly on run too.

Have you ever considered the IAC being defective. Although not for sure but this is one of a common symptom of a defective IAC motor. You might be trying to adjust or compensate for something without finding the root cause.

I would first clean the throttle body real well before I replace the IAC. As well as the IAC passages. You could try the clean the IAC for test purposes and if there is a marked difference I would then replace it.

** Just saw the IAC is replaced, missed it sorry, whatever.

Last edited by pcolt94; Feb 8, 2016 at 11:01 AM.
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Old Feb 8, 2016 | 11:14 AM
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I agree on the TB. I think he can remove the TB, remove the IAC and remove the IAC housing and clean everything and should be done every few years. That mandates new gaskets.
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Old Feb 8, 2016 | 03:27 PM
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Originally Posted by pcolt94
.

** just saw the iac is replaced, missed it sorry, whatever.
:d:d
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Old Feb 8, 2016 | 03:31 PM
  #39  
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Well, all considered from your experiences

At this point this trouble can be three thing:

1.Unmetered air from a broken hose or gasket

2.Iac count

3.defective tach
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Old Feb 8, 2016 | 03:32 PM
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Originally Posted by aklim
I agree on the TB. I think he can remove the TB, remove the IAC and remove the IAC housing and clean everything and should be done every few years. That mandates new gaskets.
Recently made. New gaskets. New Iac and Blu loctite on all screws to avoid any unmetered air from there.

Last edited by Christi@n; Feb 8, 2016 at 03:33 PM.
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