89 C4 Jerks Below 1100 Rpms
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Joined: Dec 2007
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From: Palm Coast Florida www.team-adrenalin.com
89 C4 Jerks Below 1100 Rpms
Where do I start?
Before i replaced plugs,wires,rotor,cap... the car had no throttle respose, well not what I am expected any way.Just bought the car, it has 160,000 miles on it. So did the changes and now the car at idle dips to 500 rmps at times, then idles normal after feathering the throttle up to 750 rpms or so.
Hold the throttle steady about 1200 rmps under NO load,rmps dip to 1000 then back up, this will not stop. It will happen cold or hot.
And last when you try to take off the car will buck if rpms are below 1200... NO CEL Clean MAF and new fuel filter...
Once car is rolling about 1200 it will run smooth.
Got any ideas?
Thanks
Corey
Before i replaced plugs,wires,rotor,cap... the car had no throttle respose, well not what I am expected any way.Just bought the car, it has 160,000 miles on it. So did the changes and now the car at idle dips to 500 rmps at times, then idles normal after feathering the throttle up to 750 rpms or so.
Hold the throttle steady about 1200 rmps under NO load,rmps dip to 1000 then back up, this will not stop. It will happen cold or hot.
And last when you try to take off the car will buck if rpms are below 1200... NO CEL Clean MAF and new fuel filter...
Once car is rolling about 1200 it will run smooth.
Got any ideas?
Thanks
Corey
Team Owner
Joined: Jan 2003
Posts: 20,315
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From: Summerland B.C. Canada
I would check your timing, TPS and min idle. Search for vacuum leaks, also.
89 injectors are also known for causing problems like yours. May be time for new injectors ?? Use the search engine for more info on your injectors. Here is a write up on setting the TPS and min idle.
https://www.corvetteforum.com/techti...D=55&TopicID=2
89 injectors are also known for causing problems like yours. May be time for new injectors ?? Use the search engine for more info on your injectors. Here is a write up on setting the TPS and min idle.
https://www.corvetteforum.com/techti...D=55&TopicID=2
Melting Slicks
Joined: Apr 2002
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From: St. Charles, MO Route 66 Corvette Club
Here is a write up on setting the TPS and min idle.
https://www.corvetteforum.com/techti...D=55&TopicID=2
https://www.corvetteforum.com/techti...D=55&TopicID=2
I attempted to get the author of the above tech tip to modify the procedure a few years ago and he would not agree to make the change.
Here is a similiar procedure from the C4 grand master, Gordon Killebrew on the same topic. Note the statement (item #3) on opening the EST!
I hope this info is helpful to forum members!
Team Owner
Joined: Dec 1999
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
The TPS And IAC adjustment procedures written up by Lars was (IIRC) well-received when it was posted. But Gordon Killebrew is the Guru of all things C4 so I would trust his write-up.
One thing that Gordon's write-up does not show is when the EST wire is re-connected. Is it done before setting TPS voltage or after? Obviously you have to do it before clearing the Code 42 but
What's strange is that my 87 FSM does not specifically state to unplug the EST wire before setting TPS voltage.
One thing that Gordon's write-up does not show is when the EST wire is re-connected. Is it done before setting TPS voltage or after? Obviously you have to do it before clearing the Code 42 but
What's strange is that my 87 FSM does not specifically state to unplug the EST wire before setting TPS voltage.
Melting Slicks
Joined: Apr 2002
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From: St. Charles, MO Route 66 Corvette Club
My 89 FSM has a statement that is preceded by the word IMPORTANT and it describes what can happen if the connecttion is not opened BEFORE the procedure. As for reconnecting the tan wire, the Killebrew procedure did not mention this step??? However, the tan wire should be reconnected before a battery cable is removed to clear the ECM code. This connection does not relate to the setting of the TPS.
Last edited by Sam Lam; Dec 9, 2007 at 01:51 PM.
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From: Palm Coast Florida www.team-adrenalin.com
Thank you for the help. I have read both articles and I will attempt to do the adjustment tis afternoon.
I have not worked on an american car for so long that I have forgotten a lot.
I take for granted the whole electronic tuning with a computer and an obdII imports.
I have not worked on an american car for so long that I have forgotten a lot.
I take for granted the whole electronic tuning with a computer and an obdII imports.
Race Director
Joined: Sep 2000
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From: The Top of Utah
It would be a good idea, before you do the above, to remove the IAC motor and clean both the IAC and the IAC passages in the TB. Make sure you retract the pintle before re-installation.
RACE ON!!!
RACE ON!!!
Melting Slicks
Joined: Apr 2002
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From: St. Charles, MO Route 66 Corvette Club
cscg2340: When you have a few minutes to spare, please consider updating your profile. This info is very helpful to forum members who are trying to help you. If you have questions on this, please post them 
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Joined: Dec 2007
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From: Palm Coast Florida www.team-adrenalin.com
Well I haven't had any luck yet.
Car seems to run a little different now, but not right yet.
No CEL
new Burn off relay
tps .549
idle won't really stay at 450 while doing adjustments, so did the best I could around 500
Car seems to be fine while in the throttle
The problem I have now seems like a vac leak, idles up and down while rolling, and kind of dips while stopped, but not like when the clutch is in while rolling, but if I hold a steady throttle anywhere and the throttle dips, then back up.
I am going to try replacing the cap and rotor again, and look for vac leaks.
Gonna keep pluggin away...
Car seems to run a little different now, but not right yet.
No CEL
new Burn off relay
tps .549
idle won't really stay at 450 while doing adjustments, so did the best I could around 500
Car seems to be fine while in the throttle
The problem I have now seems like a vac leak, idles up and down while rolling, and kind of dips while stopped, but not like when the clutch is in while rolling, but if I hold a steady throttle anywhere and the throttle dips, then back up.
I am going to try replacing the cap and rotor again, and look for vac leaks.
Gonna keep pluggin away...
Melting Slicks
Joined: Apr 2002
Posts: 2,118
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From: St. Charles, MO Route 66 Corvette Club
Just for whats its worth, don't forget to check for a vac leak in the power brake booster. The diaphrams go bad sometimes and a vac leak is hard to detect in this area.
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Joined: Dec 2007
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From: Palm Coast Florida www.team-adrenalin.com
Yah know I saw that information about the brake booster while I was searching forums last night, and I plan on checking it out.
Will that vaccuum leak cause no idle and popping in TB on a cold start?
The other thing that I haven't done is clean the IAC either. I will do that this weekend, maybe that will help.
Will that vaccuum leak cause no idle and popping in TB on a cold start?
The other thing that I haven't done is clean the IAC either. I will do that this weekend, maybe that will help.
