Warm Temperature, High Idle
Thread Starter
Instructor
Joined: Sep 2007
Posts: 233
Likes: 0
Warm Temperature, High Idle
I have an 86 Vette and I have been searching here and the net in general for what could cause this problem.
But First here are some known issues I think may or perhaps may not be related.
1. Coolant Temp sensor has no reading on the console constantly displays (LO)
2. Coolant level sensor (in radiator) needs replacing.
Here is what happens: Car starts great and does what I believe is called and "open loop" warm-up the idle usually hold at about 1000rpm both Oil and temp gauges read "LO"
Next: THe idle drops down to 700rpm with intermittent drops to 600rpm. This after 5 minutes or so depending on the ambient temps.
In drive the car idles at 600rpm.
After the oil Temp gauge starts to read above 200 remember my coolant temp is still reading "LO" so I do not know what that gets to.
Or even faster if I take the freeway, either scenario the idle changes.
I am assuming the Vette is now warm and in "closed loop" operation.
This is when my idle rises up 900-1000rpm in drive and up to 1300rpm in park or neutral.
If I shut the car down for as little as a minute or more the idle goes back to normal for while and eventually rises again.
Please I appreciate your thoughts and theories. Hopefully a fix!!!
But First here are some known issues I think may or perhaps may not be related.
1. Coolant Temp sensor has no reading on the console constantly displays (LO)
2. Coolant level sensor (in radiator) needs replacing.
Here is what happens: Car starts great and does what I believe is called and "open loop" warm-up the idle usually hold at about 1000rpm both Oil and temp gauges read "LO"
Next: THe idle drops down to 700rpm with intermittent drops to 600rpm. This after 5 minutes or so depending on the ambient temps.
In drive the car idles at 600rpm.
After the oil Temp gauge starts to read above 200 remember my coolant temp is still reading "LO" so I do not know what that gets to.
Or even faster if I take the freeway, either scenario the idle changes.
I am assuming the Vette is now warm and in "closed loop" operation.
This is when my idle rises up 900-1000rpm in drive and up to 1300rpm in park or neutral.
If I shut the car down for as little as a minute or more the idle goes back to normal for while and eventually rises again.
Please I appreciate your thoughts and theories. Hopefully a fix!!!
Melting Slicks
Joined: Jul 2006
Posts: 2,151
Likes: 0
From: Strongsville Ohio
a guess cause no one has responded. Check your coolant level. Replace the sensors that are missing. 200 degrees is normal. check the connection on your idle control sensor or switch whatever its called.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
I would definitely replace the coolant temp sensor. That should allow you to see the coolant temp displayed on the dash.
Does the fan come on? Is the coolant level at the top of the filler cap opening? Is there coolant in the recovery bottle and at the appropriate line?
Oil temps typically are 15-30 degrees above coolant temps once everything is up to normal operating temp. So with a 200 degree oil temp, the coolant temp should be around 180-200 and that would be normal cooling temps.
Does the fan come on? Is the coolant level at the top of the filler cap opening? Is there coolant in the recovery bottle and at the appropriate line?
Oil temps typically are 15-30 degrees above coolant temps once everything is up to normal operating temp. So with a 200 degree oil temp, the coolant temp should be around 180-200 and that would be normal cooling temps.
Thread Starter
Instructor
Joined: Sep 2007
Posts: 233
Likes: 0
I would definitely replace the coolant temp sensor. That should allow you to see the coolant temp displayed on the dash.
Does the fan come on? Is the coolant level at the top of the filler cap opening? Is there coolant in the recovery bottle and at the appropriate line?
Oil temps typically are 15-30 degrees above coolant temps once everything is up to normal operating temp. So with a 200 degree oil temp, the coolant temp should be around 180-200 and that would be normal cooling temps.
Does the fan come on? Is the coolant level at the top of the filler cap opening? Is there coolant in the recovery bottle and at the appropriate line?
Oil temps typically are 15-30 degrees above coolant temps once everything is up to normal operating temp. So with a 200 degree oil temp, the coolant temp should be around 180-200 and that would be normal cooling temps.
Thank you all very much for the replies.
Yes, the fan turns on. Yes, the coolant level is at the top of the filler cap.
Yes, there is coolant in the recovery tank.
As for the OIL TEMP reading it actually goes higher than 200. It will read as high as 220-230. In the summer when it gets up in the 80's or more it was 240. What I have noticed is that anytime the OIL TEMP reading is 200 or above is when the idle rises.
Just purchased a COOLANT TEMP SENSOR so I will put that on hopefully
tomorrow.
Any ideas why the idle is rising?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Coolant Temp Sensor has nothing to do with the Display. Display sender is between 6 & 8 on the passenger head. LO usually means it's not connected. If you take the wire and ground it against the engine, you should see 300 or so.
ECM Targeted Idle is a function of the Coolant Temp Sensor Signal which is mounted below the throttle body - you'll need a Scanner to see what it is, but doubt the Sensor is faulty because the numbers you're seeing aren't a normal target for what's burned into the ECM, even if the Coolant was below zero. Sounds more like it's got an IAC or throttle cable hangup or maybe an air leak around the throttle shaft (which seems to be common for this Year). Scan it first to see what the ECM targets for idle, Actual Idle, IAC counts and verify that the TPS is somewhere between .48 and .62 volts (or idle voltage) and that will tell you where to look next. Without that info, it's difficult to say what the problem is.
ECM Targeted Idle is a function of the Coolant Temp Sensor Signal which is mounted below the throttle body - you'll need a Scanner to see what it is, but doubt the Sensor is faulty because the numbers you're seeing aren't a normal target for what's burned into the ECM, even if the Coolant was below zero. Sounds more like it's got an IAC or throttle cable hangup or maybe an air leak around the throttle shaft (which seems to be common for this Year). Scan it first to see what the ECM targets for idle, Actual Idle, IAC counts and verify that the TPS is somewhere between .48 and .62 volts (or idle voltage) and that will tell you where to look next. Without that info, it's difficult to say what the problem is.
Thread Starter
Instructor
Joined: Sep 2007
Posts: 233
Likes: 0
Coolant Temp Sensor has nothing to do with the Display. Display sender is between 6 & 8 on the passenger head. LO usually means it's not connected. If you take the wire and ground it against the engine, you should see 300 or so.
ECM Targeted Idle is a function of the Coolant Temp Sensor Signal which is mounted below the throttle body - you'll need a Scanner to see what it is, but doubt the Sensor is faulty because the numbers you're seeing aren't a normal target for what's burned into the ECM, even if the Coolant was below zero. Sounds more like it's got an IAC or throttle cable hangup or maybe an air leak around the throttle shaft (which seems to be common for this Year). Scan it first to see what the ECM targets for idle, Actual Idle, IAC counts and verify that the TPS is somewhere between .48 and .62 volts (or idle voltage) and that will tell you where to look next. Without that info, it's difficult to say what the problem is.
ECM Targeted Idle is a function of the Coolant Temp Sensor Signal which is mounted below the throttle body - you'll need a Scanner to see what it is, but doubt the Sensor is faulty because the numbers you're seeing aren't a normal target for what's burned into the ECM, even if the Coolant was below zero. Sounds more like it's got an IAC or throttle cable hangup or maybe an air leak around the throttle shaft (which seems to be common for this Year). Scan it first to see what the ECM targets for idle, Actual Idle, IAC counts and verify that the TPS is somewhere between .48 and .62 volts (or idle voltage) and that will tell you where to look next. Without that info, it's difficult to say what the problem is.
Also the green wire is attached to the Coolant sensor between 6&8.
Going to look into the IAC and continue searching for vacuum leaks.
Lots to work with now. Thanks again!
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