Fast Idle Problem Continues
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
Fast Idle Problem Continues
This is getting frustrating. I took off the Vararam PowerWedge and I still have fast idle, though now it is down around 1300 rpm, about 200 less than with PowerWedge. Maybe that says the PowerWedge actually does increase airflow. However, that is neither here nor there.
The car runs fine, just idles fast until you come to a complete stop, then idle drops to normal 600. Also is temperature dependent. When cold, the fast idle is only 1100 rpm. Once temps exceed 200, idle goes up to 1300. Could this be a problem with the throttle body? Throttle control actuator/position sensor?
Here is how this started. CAr was running fine, then a CEL for throttle position sensor happened. I cleaned the MAF and remove the throttle body and cleaned it, both with MAF sensor cleaner. Reassembled with PowerWedge and suddenly fast idle problem. The CEL cleared on its own after about 50 miles of driving. I have tried the idle relearn procedure with no luck. I disconnected battery to reset computer, no luck.
Does disconnecting the battery reset the computer?
Any help is greatly appreciated.
The car runs fine, just idles fast until you come to a complete stop, then idle drops to normal 600. Also is temperature dependent. When cold, the fast idle is only 1100 rpm. Once temps exceed 200, idle goes up to 1300. Could this be a problem with the throttle body? Throttle control actuator/position sensor?
Here is how this started. CAr was running fine, then a CEL for throttle position sensor happened. I cleaned the MAF and remove the throttle body and cleaned it, both with MAF sensor cleaner. Reassembled with PowerWedge and suddenly fast idle problem. The CEL cleared on its own after about 50 miles of driving. I have tried the idle relearn procedure with no luck. I disconnected battery to reset computer, no luck.
Does disconnecting the battery reset the computer?
Any help is greatly appreciated.
Race Director
Joined: May 2004
Posts: 16,667
Likes: 1,209
From: Raleigh, NC
St. Jude Donor '15
100% stock tune?
If so, vacuum leak would be my first guess. Once you get under 2km/h adaptive idle kicks in and that's why it's correcting then.
Do you have access to HP Tuners, a scan tool or ELM327, or something else so you can see what's going on? If you have a smart phone, elm327's will plug into the OBD port and then you can do some basic logging with your phone. And they're like $20 (can read/reset codes too). Not as good as HP Tuners, but better than nothing and a whole lot cheaper.
If so, vacuum leak would be my first guess. Once you get under 2km/h adaptive idle kicks in and that's why it's correcting then.
Do you have access to HP Tuners, a scan tool or ELM327, or something else so you can see what's going on? If you have a smart phone, elm327's will plug into the OBD port and then you can do some basic logging with your phone. And they're like $20 (can read/reset codes too). Not as good as HP Tuners, but better than nothing and a whole lot cheaper.
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
100% stock tune?
If so, vacuum leak would be my first guess. Once you get under 2km/h adaptive idle kicks in and that's why it's correcting then.
Do you have access to HP Tuners, a scan tool or ELM327, or something else so you can see what's going on? If you have a smart phone, elm327's will plug into the OBD port and then you can do some basic logging with your phone. And they're like $20 (can read/reset codes too). Not as good as HP Tuners, but better than nothing and a whole lot cheaper.
If so, vacuum leak would be my first guess. Once you get under 2km/h adaptive idle kicks in and that's why it's correcting then.
Do you have access to HP Tuners, a scan tool or ELM327, or something else so you can see what's going on? If you have a smart phone, elm327's will plug into the OBD port and then you can do some basic logging with your phone. And they're like $20 (can read/reset codes too). Not as good as HP Tuners, but better than nothing and a whole lot cheaper.
Someone said something about a GM tool and then idle relearn procedure. Is the GM tool the same as disconnecting the battery or erasing codes with a code reader?
Race Director
Joined: May 2004
Posts: 16,667
Likes: 1,209
From: Raleigh, NC
St. Jude Donor '15
eh, I don't really think that's going to do anything. Can't hurt, but not sure it's your problem.
Do you have an iPhone or iPad? If so I would use an app called dash command. You can use it to make a basic log. Make sure to get RPM, throttle position, any of the airflow stuff you can get (MAF airflow, MAF hz, whatever else you can find), ignition timing and fuel trims (long, short, bank 1 and bank 2.. all 4). Probably some more I'm forgetting but that will help me get an idea what's going on
Just to ask the dumb question.. the car did NOT do this originally, correct?
Do you have an iPhone or iPad? If so I would use an app called dash command. You can use it to make a basic log. Make sure to get RPM, throttle position, any of the airflow stuff you can get (MAF airflow, MAF hz, whatever else you can find), ignition timing and fuel trims (long, short, bank 1 and bank 2.. all 4). Probably some more I'm forgetting but that will help me get an idea what's going on
Just to ask the dumb question.. the car did NOT do this originally, correct?
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
What is best way to check for vacuum leak? I tried propane and throttle body cleaner around the throttle body and MAF with no effect. Do I need to get some starter fluid and just spray over the engine?
Race Director
Joined: May 2004
Posts: 16,667
Likes: 1,209
From: Raleigh, NC
St. Jude Donor '15
Best way is with a smoke machine.. but most of us don't have those laying around
I've also pressurized the intake before with compressed air and sprayed soapy water all over everything. You'll see/hear bubbles if there is a leak. I took a coupler that fit the throttle body, capped off the other end and used that to seal the engine off.. then put compressed air in through the brake booster hose (keep it low, like 5psi max)
I've also pressurized the intake before with compressed air and sprayed soapy water all over everything. You'll see/hear bubbles if there is a leak. I took a coupler that fit the throttle body, capped off the other end and used that to seal the engine off.. then put compressed air in through the brake booster hose (keep it low, like 5psi max)
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
eh, I don't really think that's going to do anything. Can't hurt, but not sure it's your problem.
Do you have an iPhone or iPad? If so I would use an app called dash command. You can use it to make a basic log. Make sure to get RPM, throttle position, any of the airflow stuff you can get (MAF airflow, MAF hz, whatever else you can find), ignition timing and fuel trims (long, short, bank 1 and bank 2.. all 4). Probably some more I'm forgetting but that will help me get an idea what's going on
Just to ask the dumb question.. the car did NOT do this originally, correct?
Do you have an iPhone or iPad? If so I would use an app called dash command. You can use it to make a basic log. Make sure to get RPM, throttle position, any of the airflow stuff you can get (MAF airflow, MAF hz, whatever else you can find), ignition timing and fuel trims (long, short, bank 1 and bank 2.. all 4). Probably some more I'm forgetting but that will help me get an idea what's going on
Just to ask the dumb question.. the car did NOT do this originally, correct?
I have Vararam intake and PowerWedge. though PowerWedge is now removed with no improvement. The only issue I had with the Vararam is that when letting off the throttle the idle would momentarily rise to about 1000, then drop down to normal 600, all in about 1-2 seconds.
What is odd to me is if I have a vacuum leak that drives the idle up to 1300, how does the engine get the idle back down to 600 when the car stops moving? The vacuum leak still exists, so it should continue to fast idle, right?
Race Director
Joined: May 2004
Posts: 16,667
Likes: 1,209
From: Raleigh, NC
St. Jude Donor '15
It retards ignition timing and closes the throttle blade further to bring idle speed down.
I don't want to explain this wrong.. But, my suspicion is when adaptive idle kicks in at < 2 km/h, it's able to compensate for the extra air then. I wish I knew for sure how it works, but I was hoping to see something obvious on a log. C6's use ignition timing to help control idle speed as well as the throttle blade.. but don't have an idle air control circuit like older cars.
I've seen on my own car when I had some of the idle tables setup wrong that it would undershoot the idle and barely stay running.. then as soon as I stopped moving it would slowly correct itself. In the log you could see it was opening the throttle blade slowly.
There's a table in the computer that sets how far the throttle blade can close. I have a feeling if you could change that it would probably fix it too.. but I still think the real problem is a vacuum leak. You'd need HP Tuners to change it though.
Regardless.. vacuum leak fits the symptoms IMO
I don't want to explain this wrong.. But, my suspicion is when adaptive idle kicks in at < 2 km/h, it's able to compensate for the extra air then. I wish I knew for sure how it works, but I was hoping to see something obvious on a log. C6's use ignition timing to help control idle speed as well as the throttle blade.. but don't have an idle air control circuit like older cars.
I've seen on my own car when I had some of the idle tables setup wrong that it would undershoot the idle and barely stay running.. then as soon as I stopped moving it would slowly correct itself. In the log you could see it was opening the throttle blade slowly.
There's a table in the computer that sets how far the throttle blade can close. I have a feeling if you could change that it would probably fix it too.. but I still think the real problem is a vacuum leak. You'd need HP Tuners to change it though.
Regardless.. vacuum leak fits the symptoms IMO
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Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
It retards ignition timing and closes the throttle blade further to bring idle speed down.
I don't want to explain this wrong.. But, my suspicion is when adaptive idle kicks in at < 2 km/h, it's able to compensate for the extra air then. I wish I knew for sure how it works, but I was hoping to see something obvious on a log. C6's use ignition timing to help control idle speed as well as the throttle blade.. but don't have an idle air control circuit like older cars.
I've seen on my own car when I had some of the idle tables setup wrong that it would undershoot the idle and barely stay running.. then as soon as I stopped moving it would slowly correct itself. In the log you could see it was opening the throttle blade slowly.
There's a table in the computer that sets how far the throttle blade can close. I have a feeling if you could change that it would probably fix it too.. but I still think the real problem is a vacuum leak. You'd need HP Tuners to change it though.
Regardless.. vacuum leak fits the symptoms IMO
I don't want to explain this wrong.. But, my suspicion is when adaptive idle kicks in at < 2 km/h, it's able to compensate for the extra air then. I wish I knew for sure how it works, but I was hoping to see something obvious on a log. C6's use ignition timing to help control idle speed as well as the throttle blade.. but don't have an idle air control circuit like older cars.
I've seen on my own car when I had some of the idle tables setup wrong that it would undershoot the idle and barely stay running.. then as soon as I stopped moving it would slowly correct itself. In the log you could see it was opening the throttle blade slowly.
There's a table in the computer that sets how far the throttle blade can close. I have a feeling if you could change that it would probably fix it too.. but I still think the real problem is a vacuum leak. You'd need HP Tuners to change it though.
Regardless.. vacuum leak fits the symptoms IMO
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
Best way is with a smoke machine.. but most of us don't have those laying around
I've also pressurized the intake before with compressed air and sprayed soapy water all over everything. You'll see/hear bubbles if there is a leak. I took a coupler that fit the throttle body, capped off the other end and used that to seal the engine off.. then put compressed air in through the brake booster hose (keep it low, like 5psi max)
I've also pressurized the intake before with compressed air and sprayed soapy water all over everything. You'll see/hear bubbles if there is a leak. I took a coupler that fit the throttle body, capped off the other end and used that to seal the engine off.. then put compressed air in through the brake booster hose (keep it low, like 5psi max)
I guess one advantage is that the engine is not running so you can hear an air leak much easier.
Race Director
Joined: May 2004
Posts: 16,667
Likes: 1,209
From: Raleigh, NC
St. Jude Donor '15
Yep, you got it. It's much easier to hear them without the engine running.
I don't see why the propane trick wouldn't work, though newer cars ability to adjust ignition timing extremely quickly to correct idle speed is probably a bit less sensitive to it. Honestly I've never tried it, so I don't really know if it works on newer cars or not.
I don't see why the propane trick wouldn't work, though newer cars ability to adjust ignition timing extremely quickly to correct idle speed is probably a bit less sensitive to it. Honestly I've never tried it, so I don't really know if it works on newer cars or not.
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
OK, here is some new info. I was checking the coolant system pressure at a friend's. Coolant system holds 18 psi solid. Then I went to start the car and just a single click. Battery is only about one year old. Odd was that the dash would display like it does with the car running - all gauges working and lit up. Friend puts his jumper on it and car starts right up. Not only that, but seems that the idle problem is gone - until I get a ways down the road and the problem starts again. Now I wonder if it is an electrical issue like a battery. Voltage is at 13.8 volts.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
You have a ls3 with the blade maf. Aftermarket air cleaners had a lot of problems with that blade maf for a long time, I would have thought it would be fixed by now however.
I don't think you have a vacuum leak. A leak big enough to cause a high idle would set a CEL for running lean.
I'd suggest you put your stock air cleaner back on, unhood the battery for a minute or two and then see what happens.
Make sure you don't have any air leaks around the maf when you reinstall it.
If this fixes your car, you can do the free cold air mod and prop your shroud open with toggle bolts.
I don't think you have a vacuum leak. A leak big enough to cause a high idle would set a CEL for running lean.
I'd suggest you put your stock air cleaner back on, unhood the battery for a minute or two and then see what happens.
Make sure you don't have any air leaks around the maf when you reinstall it.
If this fixes your car, you can do the free cold air mod and prop your shroud open with toggle bolts.
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
You have a ls3 with the blade maf. Aftermarket air cleaners had a lot of problems with that blade maf for a long time, I would have thought it would be fixed by now however.
I don't think you have a vacuum leak. A leak big enough to cause a high idle would set a CEL for running lean.
I'd suggest you put your stock air cleaner back on, unhood the battery for a minute or two and then see what happens.
Make sure you don't have any air leaks around the maf when you reinstall it.
If this fixes your car, you can do the free cold air mod and prop your shroud open with toggle bolts.
I don't think you have a vacuum leak. A leak big enough to cause a high idle would set a CEL for running lean.
I'd suggest you put your stock air cleaner back on, unhood the battery for a minute or two and then see what happens.
Make sure you don't have any air leaks around the maf when you reinstall it.
If this fixes your car, you can do the free cold air mod and prop your shroud open with toggle bolts.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
I misunderstood, I thought you just added the Vararam.
Did anything else change between when it was running fine and when this started? Any mods?
Did anything else change between when it was running fine and when this started? Any mods?
Last edited by Joe_G; Sep 19, 2015 at 09:56 PM.
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
No mods. I had a CEL for throttle position sensor (P0121), so I took the throttle body off and cleaned it and the MAF sensor with MAF cleaner. Reassembled and fast idle happened immediately.
Safety Car
Joined: Nov 2007
Posts: 4,537
Likes: 1,403
From: Bethesda MD
I'd take the throttle body off and again and make sure there is nothing causing the blade to not fully shut. When cleaning, did you remove the blade and accidentally rotate it 180* ? It takes only a tiny opening to have the idle jump up. Is the TPS set properly? IIRC, the MAF is directional too; make sure that is not backward.
Also double check that you didn't crimp the gasket between the TB and intake manifold.
Also double check that you didn't crimp the gasket between the TB and intake manifold.
Tech Contributor
Joined: Jul 2002
Posts: 14,950
Likes: 264
From: St. Louis, MO
St. Jude Donor '08
I'd take the throttle body off and again and make sure there is nothing causing the blade to not fully shut. When cleaning, did you remove the blade and accidentally rotate it 180* ? It takes only a tiny opening to have the idle jump up. Is the TPS set properly? IIRC, the MAF is directional too; make sure that is not backward.
Also double check that you didn't crimp the gasket between the TB and intake manifold.
Also double check that you didn't crimp the gasket between the TB and intake manifold.
The throttle bodies are incredibly finicky, I spoke to a well known porter about how many he ruined by taking too much off. Stosjcp, how did you clean it? Any chance the blade got bent or over extended? You might want to pull it off again and double check everything.
Oh and pull your map sensor and make sure it is clean and didn't get oil in it and is properly seated and connected. I have had that problem before with mine getting oil on it and screwing it up (not a p0121 code though).
It's also possible your throttle position sensor went bad, it happens. It happened to my Harley and I had the exact same symptoms as you. New tps sensor and it's been great ever since. That was only $35 so I'm not suggesting you swap your throttle body yet, you can't buy the TPS separately.
Check also for a pinched or shorted wire in the connector when doing Ragtop's tips. Also check for any codes with your reader, some don't set a CEL.
The dead battery is odd, but did you have the doors open and radio playing for a long time while fooling around with the radiator? I'm thinking that was a fluke since your alternator seems to be fine...
Last edited by Joe_G; Sep 20, 2015 at 09:05 AM.
Thread Starter
Burning Brakes
Joined: Apr 2008
Posts: 1,190
Likes: 68
From: Woodland Hills California
I'd take the throttle body off and again and make sure there is nothing causing the blade to not fully shut. When cleaning, did you remove the blade and accidentally rotate it 180* ? It takes only a tiny opening to have the idle jump up. Is the TPS set properly? IIRC, the MAF is directional too; make sure that is not backward.
Also double check that you didn't crimp the gasket between the TB and intake manifold.
Also double check that you didn't crimp the gasket between the TB and intake manifold.