BBK 58mm throttle body idle issues....
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 2,547
Likes: 46
From: NJ
BBK 58mm throttle body idle issues....
Well ive search numerous other threads on this and have also found plenty of helpful info but Im still having issues.
Ill start with the problem first.
Car starts with NO issues and drops idle to about 800-1000 rpm (cold start) quickly. Throttle response and blips of the throttle is NO problem for the first 15-30 seconds. Then when it hits a specific time frame idle climbs to approx 3000rpms and hangs there. It will not drop.
Now the basics.
- intake mani was gasket matched and there is no throttle blade interference.
- I set the TPS to .50 vdc as stated in multiple threads I read. (some I read .5 and some I read .54 but its plus or minus .07 so either way Im in the clear.)
- Checked all my vacum conections and made sure that everything is nice and buttoned up.
What am I missing? Anyone with any experience with this issue?
Thanks
Oh yeah 1993 lt1 6spd.
Ill start with the problem first.
Car starts with NO issues and drops idle to about 800-1000 rpm (cold start) quickly. Throttle response and blips of the throttle is NO problem for the first 15-30 seconds. Then when it hits a specific time frame idle climbs to approx 3000rpms and hangs there. It will not drop.
Now the basics.
- intake mani was gasket matched and there is no throttle blade interference.
- I set the TPS to .50 vdc as stated in multiple threads I read. (some I read .5 and some I read .54 but its plus or minus .07 so either way Im in the clear.)
- Checked all my vacum conections and made sure that everything is nice and buttoned up.
What am I missing? Anyone with any experience with this issue?
Thanks
Oh yeah 1993 lt1 6spd.
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 2,547
Likes: 46
From: NJ
Oh yeah and I just went out to the car real quick and just noticed. The throttle blade arm that attaches to the throttle cable isnt touching the throttle stop? Is that normal? Is there a way to adjust the length of the throttle cable?!!?!?!
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
Maybe it's running "normal" for the first few seconds while the TB blades are open so far that its acting like a choke but with too much air. Then, as it gets warm, it starts speeding up because the throttle isn't sitting down as it should.
Seems like we had someone with a "short" throttle cable this year. If only I could remember what they bought to make it work.....cause I don't believe it's adjustable.
Maybe you have the wrong TB linkage config as compared to the original from your car?
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 2,547
Likes: 46
From: NJ
No. I don't think there's any adjustment.
Maybe it's running "normal" for the first few seconds while the TB blades are open so far that its acting like a choke but with too much air. Then, as it gets warm, it starts speeding up because the throttle isn't sitting down as it should.
Seems like we had someone with a "short" throttle cable this year. If only I could remember what they bought to make it work.....cause I don't believe it's adjustable.
Maybe you have the wrong TB linkage config as compared to the original from your car?
Maybe it's running "normal" for the first few seconds while the TB blades are open so far that its acting like a choke but with too much air. Then, as it gets warm, it starts speeding up because the throttle isn't sitting down as it should.
Seems like we had someone with a "short" throttle cable this year. If only I could remember what they bought to make it work.....cause I don't believe it's adjustable.
Maybe you have the wrong TB linkage config as compared to the original from your car?
Le Mans Master
Joined: Feb 2005
Posts: 6,485
Likes: 566
From: Clearwater Florida
..... I see you have ASR set-up ... I assume the cable in question is the one from the ASR to the throttle body ? ... I am unfamiliar with the operation of the ASR ... is there an adjustment or troubleshooting guide for it ? ... Have you tried the battery disconnect re-boot , re-learn procedure ? ... The LT motors may not have the same ECM settings , but on the MAF L98's there is a spark advance hold back built in to the program that kicks approx 20 degrees advance in at around 113 degrees ... cold start emissions .....
Last edited by C409; Sep 5, 2011 at 08:41 AM.
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 2,547
Likes: 46
From: NJ
Someone sudgested disconnecting the cable from the TB and starting it and see if the RPMs climb. If they still do then I will have to look deeper into this OR I can just diagnose it as a short cable 
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Team Owner
Joined: Jan 2003
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From: Summerland B.C. Canada
I'm not familiar with the LT1, but from what I have read over the years, the TPS is non adjustable. ECM is happy with something like .3v to .9v.
The set screw doesn't mean much if it was never set.
What does the FSM suggest for setting minimum idle ?
The set screw doesn't mean much if it was never set.
What does the FSM suggest for setting minimum idle ?
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 2,547
Likes: 46
From: NJ
TPS is adjustable if you ovlong the mounting holes which in the directions for the BBK throttle body it tells you to do...
Melting Slicks
Joined: Feb 2009
Posts: 2,072
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From: Oklahoma City OK
St. Jude '10
I'm kinda going through the same thing right now. After the rebuild I put on a Summit 58 mm and was having a problem finding a good idle. I tried a Holley 52 mm and discovered it was more trouble yet. The past couple of days I've been trying to get the idle correct but it isn't working. There is a procedure for adjusting the TB cable, accelerator cable and TV cable (if auto) all at once but it doesn't sound like your problem as it's not mine either. How did you check your TPS volts? I have learned that the 93 is not adjustable but have heard of using a dremmel to elongate the holes and make them adjustable.
Race Director
Joined: Jun 1999
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From: Merritt Ils Fl
Not sure you can absolutely say short cable but disconnecting will help eliminate some possibilities.
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 2,547
Likes: 46
From: NJ
It was because the throttle cable is too short. I disconnected the throttle cable. re-adjusted the TPS and fired her up. Idled reved and acted completely normal.
Is there an adjustment on the throttle cable length!? If not I am just going to ovlong the holes in the throttle cable bracket and move it closer to the TB...
Is there an adjustment on the throttle cable length!? If not I am just going to ovlong the holes in the throttle cable bracket and move it closer to the TB...
Burning Brakes
Joined: May 2009
Posts: 1,014
Likes: 7
From: Ft Wayne IN
Your ABS needs adjusted. It took me about half a dozen times to figure out how the manual wanted it done and to get the procedures correct. You will need a manual it explains indepth how to perform all your adjustments including idle air control and your transmission TV cable. They can all have some effect on each other and the overall tune of the engine so you want to get all correct because your tune will depend on it. If you get the TV adjustment off you can ruin your trans fairly quick. It sounds like you got the idle air control figured out but if the blades wern't set correctly and closed (not held open by cable) You will have to perform it again. The manual will also explain which adjustments to do first i.e. idle air control then ABS/TV cable then throttle position sensor etc. Get you a manual if you plan on having your vette for awhile and working on it yourself it's the best money youll ever spend on your car. I buy a manual for almost everything I own that has a motor. Good luck! 
Race Director
Joined: Nov 2003
Posts: 12,221
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From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
I notice if you do a search using "Throttle Cable" in titles only for C4 tech, there are some threads on this topic. (As I suggested earlier). By doing this, you can find a couple of people who've faces this issue, read about there approach, and/or PM them for better feedback.
Melting Slicks
Joined: Feb 2009
Posts: 2,072
Likes: 1
From: Oklahoma City OK
St. Jude '10
Here is a link to a thread with the procedure. If you can't read it let me know and I can scan it and send it to you.
http://forums.corvetteforum.com/c4-t...-problems.html
http://forums.corvetteforum.com/c4-t...-problems.html
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 2,547
Likes: 46
From: NJ
Your ABS needs adjusted. It took me about half a dozen times to figure out how the manual wanted it done and to get the procedures correct. You will need a manual it explains indepth how to perform all your adjustments including idle air control and your transmission TV cable. They can all have some effect on each other and the overall tune of the engine so you want to get all correct because your tune will depend on it. If you get the TV adjustment off you can ruin your trans fairly quick. It sounds like you got the idle air control figured out but if the blades wern't set correctly and closed (not held open by cable) You will have to perform it again. The manual will also explain which adjustments to do first i.e. idle air control then ABS/TV cable then throttle position sensor etc. Get you a manual if you plan on having your vette for awhile and working on it yourself it's the best money youll ever spend on your car. I buy a manual for almost everything I own that has a motor. Good luck!
No TV cable on mine though its stick....
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 2,547
Likes: 46
From: NJ
That's what I thought it was going to be. Your idea to elongate the bracket holes might work...as long as you can also acheive full-blade opening after the modification. At least one poster ran into that problem after his attempt to slide things forward.
I notice if you do a search using "Throttle Cable" in titles only for C4 tech, there are some threads on this topic. (As I suggested earlier). By doing this, you can find a couple of people who've faces this issue, read about there approach, and/or PM them for better feedback.
I notice if you do a search using "Throttle Cable" in titles only for C4 tech, there are some threads on this topic. (As I suggested earlier). By doing this, you can find a couple of people who've faces this issue, read about there approach, and/or PM them for better feedback.
After work today Ill have to see if I can figure out the propper procedure to get this done! Ughh...
Thread Starter
Melting Slicks
Joined: Apr 2007
Posts: 2,547
Likes: 46
From: NJ
Here is a link to a thread with the procedure. If you can't read it let me know and I can scan it and send it to you.
http://forums.corvetteforum.com/c4-t...-problems.html
http://forums.corvetteforum.com/c4-t...-problems.html
Thanks so much.
