How do I lower the engine idle speed?
Le Mans Master
Joined: Feb 2000
Posts: 7,032
Likes: 2
From: Newburgh NY
I would check the IAC's (Intake Air Controllers). There is one in each Throttle Body. Many times they go bad and the "Pintle" or plunger inside gets stuck.
They are easy to change but no cheap. I forget if it was $50 eaxch or $100 each but make sure that's it before hand.
Others have also had it happen becuase the Coolant Temp Switch at the front of the intake was bad so the motor did not know it was warmed up.
I've seen IAC's go bad and the engine will idle about 2000rpm. If it's idling fast about 1000-1200rpm I'd check the coolant circuit.
If you don't have one, I'd consider a service manual.
They are easy to change but no cheap. I forget if it was $50 eaxch or $100 each but make sure that's it before hand.
Others have also had it happen becuase the Coolant Temp Switch at the front of the intake was bad so the motor did not know it was warmed up.
I've seen IAC's go bad and the engine will idle about 2000rpm. If it's idling fast about 1000-1200rpm I'd check the coolant circuit.
If you don't have one, I'd consider a service manual.
Thread Starter
Intermediate
Joined: Dec 2008
Posts: 43
Likes: 1
i will check for vacuum leaks
and check timing tomorrow,
then tap in the IAC units... hopefully if something is stuck it will unstick
it does lower speed after warms a bit, but still it's too high and idle,
but will check coolant ciorcuit also.
well some more things to do tomorrow,
thanks!
and check timing tomorrow,
then tap in the IAC units... hopefully if something is stuck it will unstick
it does lower speed after warms a bit, but still it's too high and idle,
but will check coolant ciorcuit also.
well some more things to do tomorrow,
thanks!
I would check the IAC's (Intake Air Controllers). There is one in each Throttle Body. Many times they go bad and the "Pintle" or plunger inside gets stuck.
They are easy to change but no cheap. I forget if it was $50 eaxch or $100 each but make sure that's it before hand.
Others have also had it happen becuase the Coolant Temp Switch at the front of the intake was bad so the motor did not know it was warmed up.
I've seen IAC's go bad and the engine will idle about 2000rpm. If it's idling fast about 1000-1200rpm I'd check the coolant circuit.
If you don't have one, I'd consider a service manual.
They are easy to change but no cheap. I forget if it was $50 eaxch or $100 each but make sure that's it before hand.
Others have also had it happen becuase the Coolant Temp Switch at the front of the intake was bad so the motor did not know it was warmed up.
I've seen IAC's go bad and the engine will idle about 2000rpm. If it's idling fast about 1000-1200rpm I'd check the coolant circuit.
If you don't have one, I'd consider a service manual.
Race Director
Joined: Jan 2000
Posts: 13,018
Likes: 2,262
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Used to see them leak at the gasket between the upper plate and the lower intake manifold even when they were new.
JIM
JIM
Thread Starter
Intermediate
Joined: Dec 2008
Posts: 43
Likes: 1
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Le Mans Master
Joined: Apr 2001
Posts: 5,000
Likes: 1
From: Minneapolis, Mn USA
Replace the Coolant Temp Sensor. Its the one at the front of the intake manifold. Get the 84 style connector pigtail, its better for corrosion resistance, and splice it into the existing black and yellow wires.
My guess is this will take care of a lot of your idle issues. It did wonders for mine.
My guess is this will take care of a lot of your idle issues. It did wonders for mine.
Thread Starter
Intermediate
Joined: Dec 2008
Posts: 43
Likes: 1
so I should get a 1984 CTS (coolant temp sensor) ?
thanks!
thanks!
Replace the Coolant Temp Sensor. Its the one at the front of the intake manifold. Get the 84 style connector pigtail, its better for corrosion resistance, and splice it into the existing black and yellow wires.
My guess is this will take care of a lot of your idle issues. It did wonders for mine.
My guess is this will take care of a lot of your idle issues. It did wonders for mine.
Le Mans Master
Joined: Apr 2001
Posts: 5,000
Likes: 1
From: Minneapolis, Mn USA
I got the Napa Echlin TS4015 which had the temp sensor and the small yllw/blk pigtail. I think it even had sealant in the threads as bought.
Splice it into the ylw/blk wires to match the pigtail colors.
Splice it into the ylw/blk wires to match the pigtail colors.
Thread Starter
Intermediate
Joined: Dec 2008
Posts: 43
Likes: 1
Hello,
I ran the car again today,
i think the stock idle caps are still in place, if i was looking at the correct thing.
idle on cold start is 2000 to 2200, slowly goes down to 1400 to 1600 after fully warmed up.
Would this mean the IAC is OK as it is functioning to lower the idle?
I used carb cleaner and propane to check for vacuum leaks, could not find any.
Where exactly is the CTS (coolant temp sensor) located?
Will someone post a pic of it?
My check engine lamp still does not work,
is there anything else that could cause the high idle?
Thanks!
.
I ran the car again today,
i think the stock idle caps are still in place, if i was looking at the correct thing.
idle on cold start is 2000 to 2200, slowly goes down to 1400 to 1600 after fully warmed up.
Would this mean the IAC is OK as it is functioning to lower the idle?
I used carb cleaner and propane to check for vacuum leaks, could not find any.
Where exactly is the CTS (coolant temp sensor) located?
Will someone post a pic of it?
My check engine lamp still does not work,
is there anything else that could cause the high idle?
Thanks!
.
Thread Starter
Intermediate
Joined: Dec 2008
Posts: 43
Likes: 1
Hi,
Ok, I replaced the CTS and the idle seemed a bit higher at first then went down as before to maybe a bit higher than it was before the change.
I connected a Snap-On MT2500 scanner,
"NO CODES PRESENT"
exhaust is reading "RICH"
i noticed the TPS (Throttle Position Sensor) was reading 2.67 and the scanner said it should read 0.51 (+-0.05)
I had a used TPS i picked up, 'just in case', I replace the TPS and adjusted to spec 0.51 the idle came down slightly, but still in the 1425 rpm range.
If i unplug the MAP (manifold absolute pressure) sensor the idle gets rough and increases.
if i unplug the vacuum hose to the MAP sensor and cap the t/b orfice it connected to, idle drops to a more normal 950 rpm.
any ideas or thoughts on what could be the problem?
another note; the car was knocking (pinging loud) quite a bit the time i drove it, i attibuted that to bad gas as this car sat for unknown months before i got it.
thank you!
Ok, I replaced the CTS and the idle seemed a bit higher at first then went down as before to maybe a bit higher than it was before the change.
I connected a Snap-On MT2500 scanner,
"NO CODES PRESENT"
exhaust is reading "RICH"
i noticed the TPS (Throttle Position Sensor) was reading 2.67 and the scanner said it should read 0.51 (+-0.05)
I had a used TPS i picked up, 'just in case', I replace the TPS and adjusted to spec 0.51 the idle came down slightly, but still in the 1425 rpm range.
If i unplug the MAP (manifold absolute pressure) sensor the idle gets rough and increases.
if i unplug the vacuum hose to the MAP sensor and cap the t/b orfice it connected to, idle drops to a more normal 950 rpm.
any ideas or thoughts on what could be the problem?
another note; the car was knocking (pinging loud) quite a bit the time i drove it, i attibuted that to bad gas as this car sat for unknown months before i got it.
thank you!
Hello,
I ran the car again today,
i think the stock idle caps are still in place, if i was looking at the correct thing.
idle on cold start is 2000 to 2200, slowly goes down to 1400 to 1600 after fully warmed up.
Would this mean the IAC is OK as it is functioning to lower the idle?
I used carb cleaner and propane to check for vacuum leaks, could not find any.
Where exactly is the CTS (coolant temp sensor) located?
Will someone post a pic of it?
My check engine lamp still does not work,
is there anything else that could cause the high idle?
Thanks!
.
I ran the car again today,
i think the stock idle caps are still in place, if i was looking at the correct thing.
idle on cold start is 2000 to 2200, slowly goes down to 1400 to 1600 after fully warmed up.
Would this mean the IAC is OK as it is functioning to lower the idle?
I used carb cleaner and propane to check for vacuum leaks, could not find any.
Where exactly is the CTS (coolant temp sensor) located?
Will someone post a pic of it?
My check engine lamp still does not work,
is there anything else that could cause the high idle?
Thanks!
.
Le Mans Master
Joined: Apr 2001
Posts: 5,000
Likes: 1
From: Minneapolis, Mn USA
Vacuum leak somewhere is my guess.
Try spraying carb cleaner around the edges of the top plenum gasket and TB base gaskets to see if there is an increase in idle.
Plug off the brake vacuum booster and then the headlights manifold vacuum fittings to see if this changes your idle-one at a time.
Try spraying carb cleaner around the edges of the top plenum gasket and TB base gaskets to see if there is an increase in idle.
Plug off the brake vacuum booster and then the headlights manifold vacuum fittings to see if this changes your idle-one at a time.
Thread Starter
Intermediate
Joined: Dec 2008
Posts: 43
Likes: 1
and the propane make it speed up?
If i spray carb cleaner in the TB engine slows down.
that is why i tried propane too, that make the engine speed up if put in the TB.
I removed the vac lines one by one, each increases the idle until i cap them off,
no decrease in idle below the problem higher idle speed,
EXCEPT when Unplugging the MAF vac line
resulted in lower idle when unplugged, and even lower when capped off.
.
Thread Starter
Intermediate
Joined: Dec 2008
Posts: 43
Likes: 1
Thread Starter
Intermediate
Joined: Dec 2008
Posts: 43
Likes: 1
Hi,
I rechecked all vacuum hoses, i removed all and capped w/exception of the MAP hose. = NO change.
I replaced the MAP hose. = NO change, Still high idle 1425-1500 rpm.
I replaced the MAP with what should be a good used part from a salvage yard. = NO change.
I replaced all other vacuum hoses I could find, as expected = NO change.
I ran the car and unplugged the IACs on operating temp running engine. = NO change.
THEN, I put my hand over a 3/4 inch aluminum tube that comes out of the passenger side valve cover, and VOILA, the idle drops to 900 rpm!
This tube connects from the valve cover to the air cleaner.
So, my question now is;
WHY?
What can be the problem?
Does this connect to the EGR in any way?
Thank you!
.
I rechecked all vacuum hoses, i removed all and capped w/exception of the MAP hose. = NO change.
I replaced the MAP hose. = NO change, Still high idle 1425-1500 rpm.
I replaced the MAP with what should be a good used part from a salvage yard. = NO change.
I replaced all other vacuum hoses I could find, as expected = NO change.
I ran the car and unplugged the IACs on operating temp running engine. = NO change.
THEN, I put my hand over a 3/4 inch aluminum tube that comes out of the passenger side valve cover, and VOILA, the idle drops to 900 rpm!
This tube connects from the valve cover to the air cleaner.
So, my question now is;
WHY?
What can be the problem?
Does this connect to the EGR in any way?
Thank you!
.