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L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

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Old 04-27-2010, 09:26 PM   #1
steve40th
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Default UPDATE #2, Still idling high. LT1 Idle is too high...1993

Hey Guys. Well after getting my transmission done, I drove her home and parked her. No issues technically.
Well I went to drive it today, and whether it is cold or hot the idle is between 1200-1300 rpms. If I turn the AC on the idle drops 200 rpm. I can put it in gear and it wont die with/without AC. I Ohmed the IAC, good. I reset IAC according to standard OP of years I have done it. No dice. I looked for vacuum leaks with bubbly water solution, no vacuum issues. I then replaced the chip, 1993 Vette, with 3 different programs I have from different tuners. No change.
I then opened the throttle body a quarter turn at a time, and closed it to where it was not even touching the lever.
No change.
The IAC is a year old, and is very clean, as I never drive the damn thing.
So, what else can cause a high idle, as I have no codes?
Can a throttle body be sticking? Should I taake it off and clean it?
I am open to suggestions.
Thanks, Steve

Last edited by steve40th; 05-01-2010 at 03:28 AM.
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Old 04-28-2010, 01:29 AM   #2
surfer92
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Did they reset the TV cable?

You checked ALL vacuum hoses and connections, not just by the intake?

Did you check the 2 ground straps, to see if they were connected to the bellhousing?

My 93 had a high idle and it was a combination of a vacuum leak at the FPR and I had to take off the IAC and turn the pintle under a 1 1/8" and reinstall as new. It was like the IAC lost its place or was sticking.
I did clean it w/throttlebody cleaner.
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Old 04-28-2010, 02:07 AM   #3
steve40th
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Quote:
Originally Posted by surfer92 View Post
Did they reset the TV cable?

You checked ALL vacuum hoses and connections, not just by the intake?

Did you check the 2 ground straps, to see if they were connected to the bellhousing?

My 93 had a high idle and it was a combination of a vacuum leak at the FPR and I had to take off the IAC and turn the pintle under a 1 1/8" and reinstall as new. It was like the IAC lost its place or was sticking.
I did clean it w/throttlebody cleaner.
It ran fine when I brought it home a couple/three weeks ago. It idled fine etc. Its when I ran it today, it all of a sudden ran high.
I will re-check all vacuum lines, even though it is a MAP car it shouldn't affect it.
I set the TV cable via FSM and with pan off to verify the compliance at idle and WOT.
I will re-clean the IAC too.
I just re-cleaned the throttle body off of the engine. It was dirty, but not sticky or clogged.
The IAC is exactly at 1 1/8" right now.
Ground straps were installed as I did it myself.
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Old 04-28-2010, 02:32 AM   #4
Ramrod92
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Steve, do you have access to a good scan tool that will show realtime readings?
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Old 04-28-2010, 04:17 AM   #5
steve40th
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Quote:
Originally Posted by Ramrod92 View Post
Steve, do you have access to a good scan tool that will show realtime readings?
Yes, I have TTS Datamaster. I may do it tomorrow night. I also reprogrammed another chip where idle is 900 in P/D and neutral. I will do that last. I really cleaned the heck out of the T body and all associated housing and IAC/. Test it tommorow and datalog.
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Old 04-28-2010, 12:33 PM   #6
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IAC pintle needs to be under 1 1/8" and check for a leak at the MAP sensor. I had one there once, drove me crazy trying to find that one.
Check for a leak at the power booster, I have a leak there now.

FSM says to check:
PCV operation
IAC
MAP
EGR
Check A/C operation, if ECM thinks A/C is on, it will raise the idle.
Crankcase ventilation, i.e. tube running from pass. side valve cover to TB
PNP switch circuit, Park/neutral switch.
AIR system
Altenator putting out > 16v or < 9v
EVAP system - see my post about this
O2's
leaking FI
fuel in FPR
Leaking exhaust manifold

This should keep you busy for a while!!
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Old 04-28-2010, 01:00 PM   #7
steve40th
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PCV operation-GOOD
IAC-CHecked electrically and its clean
MAP-Will Check
EGR -DOnt have one
Check A/C operation, if ECM thinks A/C is on, it will raise the idle. Will check Datamaster while running
Crankcase ventilation, i.e. tube running from pass. side valve cover to TB-New hose.(MAP car doesnt affect it anyways
PNP switch circuit, Park/neutral switch.-Car wont start unless in Park
AIR system-Dont have one
Altenator putting out > 16v or < 9v-New Battery alternator 13.25-13.5
EVAP system - see my post about this
O2's-New, no leaks and will re-verify with Datamaster. They are fairly new and heated
leaking FI-Nope
fuel in FPR-Nope, smells good
Leaking exhaust manifold-Nope
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Old 04-28-2010, 02:33 PM   #8
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Car should start in neutral and if switch not working properly, could fool ECM into thinking it is in gear, when not.

How did you check the IAC, hope not through Datamaster, as that just shows what the ECM wants the IAC to do, not what it is doing.
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Old 04-28-2010, 11:32 PM   #9
steve40th
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Quote:
Originally Posted by surfer92 View Post
Car should start in neutral and if switch not working properly, could fool ECM into thinking it is in gear, when not.

How did you check the IAC, hope not through Datamaster, as that just shows what the ECM wants the IAC to do, not what it is doing.
I checked he IAC via a meter as I checked it like I have stated for a couple years, with resistance through A-B and C-D terminals. I also am the one who has been preaching that the Datamaster, or any scan tool, can only show what the IAC is being told to do via the ECM, as there is no way I know of where you can actually see what the IAC is doing.
But, I will Datamaster the car in a couple hours, as I dont want to pollute the house causing my wife and daughter to choke on non catted engine.
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Old 04-29-2010, 01:42 AM   #10
steve40th
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Found the smoking gun. A cut ground wire(right O2 sensor), cut in half, as it was pinched by the bell housing by the transmission dipstick tube bracket bolt hold down tab.

Last edited by steve40th; 04-29-2010 at 02:39 AM.
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Old 04-29-2010, 10:14 AM   #11
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Nice find. Don’t think anyone would ever suggest that. I am surprised the effect it did have though. You would think the A/F mixture (fuel trim) would show up different. Go figure.

Does the 93 have heated O2s. Maybe the heater wire was broken………maybe?

Glad you got it right, will store this one in memory.
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Old 04-29-2010, 11:26 AM   #12
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Quote:
Originally Posted by pcolt94 View Post
Nice find. Don’t think anyone would ever suggest that. I am surprised the effect it did have though. You would think the A/F mixture (fuel trim) would show up different. Go figure.

Does the 93 have heated O2s. Maybe the heater wire was broken………maybe?

Glad you got it right, will store this one in memory.
Only had heated o2's on LT5, LT1 was non-heated.
Unless he has headers, then he most likely has heated.

Funny how when you know it should be an easy problem to diagnose, it turns out to be a difficult task, bet ole Murphy had a good laugh.
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Old 04-29-2010, 12:19 PM   #13
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Quote:
Originally Posted by surfer92 View Post
Only had heated o2's on LT5,

??LT1 was non-heated.??

Unless he has headers, then he most likely has heated.
Humm… Even though I have not changed my O2 sensors yet. I believe that the times I have been looking at the FSM in the past for the 94, LT1, it did look that it was heated. (From memory, right now).

I will look again tonight.
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Old 04-29-2010, 12:34 PM   #14
steve40th
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I have long tube headers and Iinstalled heated O2's. The DTC never showed as it was not out of spec, just lean on one O2 sensor. When I reinstalled the transmission a few weeks back the dipstick tube pinched the wire. It was the ground wire.
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Old 05-01-2010, 03:29 AM   #15
steve40th
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Okay, to make a long story short. No vacuum leaks, no DTC's, heated O2's with long tubes. Engine ran sweet about three weeks ago. Came back from TAD, now it wont idle below 1400 rpm. Turn AC on it goes down. O2's are working fine using my scan tool.
I sprayed bubbly water over all hoses etc and nothing changed. No exhaust leaks. Cleaned the living heck out of the throttle body and IAC housing.
IAC is very clean, and I didnt clean it as it is a couple years old.
I checked the pins for resistance and the IAC is within specs. I also connected it and put it in a bag and turned the key on, NOTHINg, it didnt move at all. So, being a 93, I pulled the spring down and turned the IAC out and in for several test to see if it would move. Nothing.
I then put it back in the throttle body at 1", 1 1/8", and 1 3/16 " without the connector and the idle changed, got higher as I went shorter and at 1 3/16 it was at 1100. (My engine chip is set for 850, and I also tried three different older tunes that worked prior to all this and the idle never changed).
So, I reconnected IAC connector, started it up and no change, turned ac on and it brought it down 200rpm.
Took it out and it didnt change length.
Should it change length when it was out and connected and I turn the key on? Should it have changed length within the engine when running and ac turned on?
Can an IAC be bad, yet show its resistance reading being good?
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Old 05-01-2010, 04:07 AM   #16
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It never seems to end does it Steve........What is it about these cars that when you put them to sleep for a while they wake back up in a bad mood!

Anyway, hope you get it squared away.
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Old 05-01-2010, 04:22 AM   #17
steve40th
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Someday it will run okay. I do know they need to be driven. I am thinking the IAC motor is locked up.
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Old 05-01-2010, 04:25 AM   #18
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Have a Tech I? Mine has a test you can run on the IAC.
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Old 05-01-2010, 05:13 AM   #19
steve40th
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Have a Tech I? Mine has a test you can run on the IAC.
Nope, all I have is TTS Datamaster. It just shows you real-time data, with the exception of the IAC of course as all you can see on most scanners is what the ecm is telling it to do.
Does the TECH 1 actually move the IAC motor via pulses to see if it is actually moving?
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Old 05-01-2010, 05:17 AM   #20
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Quote:
Originally Posted by steve40th View Post
Does the TECH 1 actually move the IAC motor via pulses to see if it is actually moving?
Yep, it has several different test that can be run. Of course a Tech II is the way to go but way to pricey for me.
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Old 05-01-2010, 05:17 AM
 
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