'91 exessive idle?
Thread Starter
Instructor
Joined: Oct 2005
Posts: 143
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From: Lincolnshire,ENGLAND
'91 exessive idle?
Yesterday my 1991 L98 started idleing at 2000 rpm ! 
At first start up it idles at 1600 rpm then after warm up it drops to 1100 rpm ?, but then on a jurney it will idle at 2000 rpm.
Before this problem started it use to warm up at 1100 and drop to about 850 rpm which is fine.
Water temp is fine.
Checked for hose leaks and throttle linkage/cable problems- all seem fine.
Ecm & ccm not throwing any codes.
Also fitted a new IAC valve three weeks ago after low idle/cutting out problems.Cleaned throttle body and check for correct pintle length when installing new IAC,started up as per workshop manual to set new IAC valve-no problems then drve better than ever and had a steady idle.
I have no idea whats causing this?
Any ideas?
At first start up it idles at 1600 rpm then after warm up it drops to 1100 rpm ?, but then on a jurney it will idle at 2000 rpm.
Before this problem started it use to warm up at 1100 and drop to about 850 rpm which is fine.
Water temp is fine.
Checked for hose leaks and throttle linkage/cable problems- all seem fine.
Ecm & ccm not throwing any codes.
Also fitted a new IAC valve three weeks ago after low idle/cutting out problems.Cleaned throttle body and check for correct pintle length when installing new IAC,started up as per workshop manual to set new IAC valve-no problems then drve better than ever and had a steady idle.
I have no idea whats causing this?
Any ideas?
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
My first two guesses are the engine coolant temperature sensor (test it, don't blindly replace it) and a vacuum leak. Every time that happens to me, it's an intake manifold epoxy patch that has failed.
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Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by Casethecorvetteman
with a digital volt meter, im not sure what reading youll be looking for though, someone else will know the procedure for that. Did you check all the wiring for any shorts?
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Le Mans Master
Joined: May 2005
Posts: 5,214
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From: Queensland, AUSTRALIA
Originally Posted by CFI-EFI
I think think the desired numbers are in the FSM, but simply observing that the resistance changes with the temperature changes will confirm that it is operating.
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Thread Starter
Instructor
Joined: Oct 2005
Posts: 143
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From: Lincolnshire,ENGLAND
Originally Posted by CFI-EFI
I think think the desired numbers are in the FSM, but simply observing that the resistance changes with the temperature changes will confirm that it is operating.
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Thanks, I'll check that out.All i could find in the FSM is what to look for with a tech1.
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Thread Starter
Instructor
Joined: Oct 2005
Posts: 143
Likes: 0
From: Lincolnshire,ENGLAND
checked the coolant temp sensor/wireing/connections etc. all fine.
Had a good look at all the throttle body linkages and it looks like the blades arnt returning back all the way?
At the front/drivers side of the throttle body near the top, a part of the linkage sits againts a small adjuster screw-after giving the engine a few revs it returns back,but not all the way-stands about 1mm off the screw.
If i stab the throttle it will return back all the way though?
So i guess its binding or something.The center section of the return spring also seems slack-is this supposed to be like this?
Are their any adjustments i can make? or is their anything else that i can do to remedy this problem?
BTW thanks for all the info up to now.
Had a good look at all the throttle body linkages and it looks like the blades arnt returning back all the way?
At the front/drivers side of the throttle body near the top, a part of the linkage sits againts a small adjuster screw-after giving the engine a few revs it returns back,but not all the way-stands about 1mm off the screw.
If i stab the throttle it will return back all the way though?
So i guess its binding or something.The center section of the return spring also seems slack-is this supposed to be like this?
Are their any adjustments i can make? or is their anything else that i can do to remedy this problem?
BTW thanks for all the info up to now.
Drifting
Joined: May 2005
Posts: 1,370
Likes: 1
From: Raleigh NC
Sounds like a vacuum link. Carefully spray some starting fluid around the intake and TPI and see if the rpms increase. If so, you have a leak. Be careful, starting fluid is flammable...but you will find a leak...just don't go crazy with it.
Advanced
Joined: Oct 2005
Posts: 84
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From: Vancouver British Columbia
WOW you have the exact same problem as me.
"high idle started "out-of-the blue", why?"
It started one day, idles at 1,200 at start, moves quickly to 1,800 as it warms up and it is at 2,000 when hot.
But it is not my throtle body linkage for sure.
"high idle started "out-of-the blue", why?"
It started one day, idles at 1,200 at start, moves quickly to 1,800 as it warms up and it is at 2,000 when hot.
But it is not my throtle body linkage for sure.
Thread Starter
Instructor
Joined: Oct 2005
Posts: 143
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From: Lincolnshire,ENGLAND
double checked for vacuum leaks-all seems fine, also checked EGR valve which is fine.
New pcv valve fitted couple of month ago.
rkubara- Same problem! This car is my daily driver,at stop lights etc i've found if i 'stab' the throttle it will drop down to about 1100rpm.Mine is also a stick shift.
Surely if their was some kind of vac leak the rpms wouldnt drop back to normal(ish) with a stab of the accelorator pedal?
New pcv valve fitted couple of month ago.
rkubara- Same problem! This car is my daily driver,at stop lights etc i've found if i 'stab' the throttle it will drop down to about 1100rpm.Mine is also a stick shift.
Surely if their was some kind of vac leak the rpms wouldnt drop back to normal(ish) with a stab of the accelorator pedal?
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by 77vetteuk
Had a good look at all the throttle body linkages and it looks like the blades arnt returning back all the way?
At the front/drivers side of the throttle body near the top, a part of the linkage sits againts a small adjuster screw-after giving the engine a few revs it returns back,but not all the way-stands about 1mm off the screw.
At the front/drivers side of the throttle body near the top, a part of the linkage sits againts a small adjuster screw-after giving the engine a few revs it returns back,but not all the way-stands about 1mm off the screw.
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Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by rkubara
If CFI-EFI is right, then I would think spraying starter fluid at the Throttle body linkage and/or at the TPS (other side) would increase the RPM.
Originally Posted by CFI-EFI
Besides the sticking, there usually is a small vacuum leak between the shaft and the TB casting, adding to the problem.
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Thread Starter
Instructor
Joined: Oct 2005
Posts: 143
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From: Lincolnshire,ENGLAND
Had my suspisions about the throttle shaft/worn throttle body- makes sense though.
Car has only done 64,000 do they wear out this quick?
I will look into this thoroghly before i lay out £££ for a new TB.
Is their a TB rebuild kit or a shaft sleeve kit available? Havent seen any in the usual vette parts cataloges,havent even seen replacement rochester throttle bodys either?
Car has only done 64,000 do they wear out this quick?
I will look into this thoroghly before i lay out £££ for a new TB.
Is their a TB rebuild kit or a shaft sleeve kit available? Havent seen any in the usual vette parts cataloges,havent even seen replacement rochester throttle bodys either?
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by 77vetteuk
I will look into this thoroghly before i lay out £££ for a new TB.
RACE ON!!!
Thread Starter
Instructor
Joined: Oct 2005
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From: Lincolnshire,ENGLAND
OK its not the trottle body,just installed a BBK TB-still have the same problem!
The original was well worn though-in comparasen with the BBK the original TB had a hell of alot of play at the shaft,surprising how much after only 64,000 miles.The BBK closes alot tighter-you can feel it in the gas pedel when you brake oben the butterflys-stiff!
Still returns all the way back with a stab of the throttle pedal like before.Really dont know what to check next?
Could it be the ECM sending B/S info to the IAC valve?
Seen other posts in the past before with this exact same problem,but no-one seems to put a final post saying what caused it?
This has got me beat now
The original was well worn though-in comparasen with the BBK the original TB had a hell of alot of play at the shaft,surprising how much after only 64,000 miles.The BBK closes alot tighter-you can feel it in the gas pedel when you brake oben the butterflys-stiff!
Still returns all the way back with a stab of the throttle pedal like before.Really dont know what to check next?
Could it be the ECM sending B/S info to the IAC valve?
Seen other posts in the past before with this exact same problem,but no-one seems to put a final post saying what caused it?
This has got me beat now
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
You need to see how many counts are being commanded to the IAC, desired idle and actual and from there you can also check the TPS (I'd make sure it's at .54 - though L98 specs are that number +/- .08 - get above .62 and the ECM is going to think it's accelerating and the IAC goes out of the picture). You can also check the CTS signal, so, if you have a scanner, hook it up and capture this data. Otherwise, buy or borrow one. In the interim, depress the accelerator slightly and start it. Let it run for 10 seconds and turn it off for 5 seconds. Restart and see if that cures it.
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
Originally Posted by 77vetteuk
OK its not the trottle body,just installed a BBK TB-still have the same problem!
Originally Posted by 77vetteuk
The BBK closes alot tighter-you can feel it in the gas pedel when you brake oben the butterflys-stiff!
RACE ON!!!