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Old 04-27-2021, 02:05 PM   #1
snowkilts
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Default High idle when car is warm

Hi, can anyone give me some suggestions as to what to look at for high idle that only occurs when the vehicle is fully warmed up?

I've seen a few threads on this, but none seem to be spot on to my issue.

I have a (new to me) 2007 Aura XE with the 3.5L V6. Approx. 140K miles.

From a cold start, the idle is between 700-800 rpm. As it warms up, when I touch the throttle, the rpms go up normally, then come back down to a higher level. When fully warmed up, the idle settles at around 2350 and stays there.

I did remove and clean the throttle body a few weeks ago. Unfortunately I did not really drive it before this, so I don't know if the problem was already happening. I did not use a new gasket on the throttle body.

I have a Bluedriver scan tool which shows me that the accelerator is returning fully, it's not stuck or anything. Also the throttle is being commanded to higher levels, so it's not sticking.

I've tried several times to do the "throttle relearn", but I'm not seeing it happen. Not sure what's going on there.

I would appreciate any suggestions of things to look at.
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Old 04-27-2021, 06:07 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: High idle when car is warm

No expert on Auras but do have knowledge of EFI systems and still learning from these forums. If I'm not mistaken, Auras replaced L300s mainly for GM to have a domestic engine. L300s ancestry came from Europe as either Saabs or Vectras. The first to adopt the euro 3.0L V6 engine here was the Cadillac Catera, the baby Cadillac. It had a short run before Saturn decided to bring over the Vectra with USA mods to comply with american vehicle configurations different from europe, creating the L200/L300.

Auras with 3.6L V6 engines have more power than the 3.0L. And I see rockauto listing replacement throttle position sensors for Auras. The L300 throttle bodies are not serviceable - the entire throttle is replaced as one unit.

On virtually every engine starting up cold, the idle rpm is higher to account for the extra fuel needed for cold engine startup. As the engine warms up, the ecm monitors sensors and continually brings the high idle down until reaching normal warm idle rpm. Your descriptions seems to be a reversal with a normal idle at startup and rising (incorrectly) after warm up. This is odd and either requires a complicated diagnosis or not. I think everyone wants to easy diagnosis over a complicated one.

The coolant sensor is a key part for the ecm in determining startup idle rpm whether in subfreezing or desert heat temperatures. If you have a reader to display data, examine cold coolant temps before starting by just turning on ignition. Coolant temps should be very close to ambient outdoor temps. After a warm up, coolant should be between 185F-200F. These two values, cold engine reflecting ambient temps, warm engine temps reflecting thermostat regulating operating temps, ensures the coolant sensor is operating as designed.

The ecm uses the coolant sensor as the main input to adjust engine rpm. The throttle position sensor tells the ecm throttle opening. The S-series forums are littered with faulty tps' raising idle rpm. The test for it is to shut off the engine when a high idle occurs then restart. If idle returns to normal, the tps is the problem as the high idling returns at random. Replacing it solves the problem. I do not know if Auras suffer from this too as no one in the Aura forums have posted about it. None of the other Saturn models suffer from worn throttle position sensors. There may be a way to monitor tps via a reader displaying tps position.

Using your reader, check tps position after turning on ignition, engine off then after starting up. Note cold engine or warm. Check tps position after warm up. Your normal idle should display tps value for reference against a higher rpm. Examine the throttle plate position too, at cold engine startup and again after high idle occurs.

A test for a vacuum leak from reusing a throttle body gasket would be spraying solvent or plain water on the gasket area. Any major change in rpm would indicate a vacuum leak.

Some suggestions given are a start. What's standby battery voltage? voltage with normal idle and high idle? There may be more troubleshooting if nothing is revealed during these troubleshooting suggestions.
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Old 04-28-2021, 08:59 AM   #3
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Default Re: High idle when car is warm

Quote:
Originally Posted by fdryer View Post
On virtually every engine starting up cold, the idle rpm is higher to account for the extra fuel needed for cold engine startup. As the engine warms up, the ecm monitors sensors and continually brings the high idle down until reaching normal warm idle rpm.
Hi, thanks for responding. My car is in fact doing this part correctly.

I did two runs logging various parameters with my Bluedriver, one without coolant temp, and one with. In the run 1, I started the car with the logger connected, and the idle does go up for a couple of minutes and then back down.

Run 1 -- no coolant temp

Run 2 -- with coolant temp

Quote:
Originally Posted by fdryer View Post
The coolant sensor is a key part for the ecm in determining startup idle rpm whether in subfreezing or desert heat temperatures. If you have a reader to display data, examine cold coolant temps before starting by just turning on ignition. Coolant temps should be very close to ambient outdoor temps. After a warm up, coolant should be between 185F-200F.
It's not in the logging data, but I just checked the coolant temp with the engine off and cold, and it reads 63F, which is very close to the present outside temp. The coolant temp in "Run 2" topped out at 198F after 20 minutes of operation, so it sounds like this is about right.

Quote:
Originally Posted by fdryer View Post
The ecm uses the coolant sensor as the main input to adjust engine rpm. The throttle position sensor tells the ecm throttle opening. The S-series forums are littered with faulty tps' raising idle rpm. The test for it is to shut off the engine when a high idle occurs then restart. If idle returns to normal, the tps is the problem as the high idling returns at random.
In "Run 1", I turned off the ignition at time index 1530. After turning in back on, the idle returned to normal. Later at around time index 1650, I blipped the throttle and the idle went up to 2350 or so. Would you say I need to replace the throttle body based on this? I'm a little puzzled by this, because it appears to me from looking at the log that the throttle is being commanded to go up. For example:

time 1640.4 rpm 712 commanded throttle 5.5% actual throttle 16.9

Then a few seconds later:

time 1668 rpm 2328 commanded throttle 23.1% actual throttle 29

I would have thought that a high idle would be caused by the TPS saying that the throttle did not go up when told to, but that does not appear to be the case.

I will also check the other items you suggested.
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Old 04-28-2021, 09:10 AM   #4
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Default Re: High idle when car is warm

One piece of information. I've seen other posts indicating that there is a "throttle relearn" that's supposed to happen when the ignition is turned on but no pedal inputs occur within 30 seconds. I've tried several times to observe this (looking at the butterfly), but have been unable to get it to happen.
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Old 04-28-2021, 01:08 PM   #5
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2003 L-Series 3.0L Sedan
Default Re: High idle when car is warm

I'm a little slow at examining spread sheets. It'll take some time to absorb data then draw a picture in my mind. Perhaps others can interpret the data quicker.

Your brief descriptions of cold engine startup with a high idle returning to normal after some minutes pass indicates a normal function. This says the ecm is operating correctly, commanding throttle up, monitoring sensors and gradually lowering high idle back to normal idle. The feedback circuits between throttle position sensor and ecm seem correct at this point and should be no different at other throttle positions when pressing the gas pedal. Can we presume the check engine light is off with zero error codes?

It would be great to have service manuals rather than rely on online hearsay unless information is from a reliable source. There's always possibilities of misinformation disseminated as facts when it's wrong after careful research. I try relying on GM service manuals and reprint verbatim when possible to leave no room for misinterpretations. L300s have throttle relearning procedures as you've described and I've performed it several times. I don't know if Auras with similar drive by wire throttle and pedal have this feature. It would make sense to have it but again, without service manuals or a third party expert with ASE certification offering help online, sources of info must be held with a certain amount of scepticism until proven factual. There is another easy alternative to checking throttle and pedal operation.

Testing throttle and pedal from home isn't any different from older carburetor systems. Electronic drive by wire just means pedal is sending signals to the ecm with the ecm commanding the electric throttle to open or close the throttle plate in direct proportion to pedal travel. Have someone in the car move the pedal as you observe throttle plate movement. Pedal is master telling ecm to move throttle. Pedal and throttle have feedback sensors to the ecm for safety against any unforeseen unintended acceleration situations. Even when battery power is interrupted in a crash, the throttle has a built in strong return spring to close throttle against a runaway engine. You can, with ignition OFF, depress the throttle plate with fingers to feel the resistance against opening. Since its geared, depress the throttle plate slowly. I've done on my L300 without issues despite incorrect hearsay against doing this. Never manually move throttle plate with ignition On as the EFI system is live and the ecm presets throttle for starting. This means power is holding the throttle plate in position and cannot move when pressed. Damage can result if pressure is applied with ignition on as the throttle is set according to pedal position. With ignition off, moving throttle plate manually for cleaning ensures damage won't occur.
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Old 04-28-2021, 10:05 PM   #6
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Default Re: High idle when car is warm

I'm maneuvering the spreadsheet header down to startup and again as high idle warm up began lowering. I don't see anything standing out with what appears to be normal data. I may be going out on a limb but think there may too much data - getting lost in a sea of it. Before this thread, I'm accustomed to a log of one point in time, described as freeze frame data where a snapshot of info is captured. This can be baseline data before starting, after startup, then after the engine reaches operating temperature. Three lines of data. When an error occurs illuminating the engine light, the OBD II system captures data at the moment the error occurred for display when retrieved by readers capable of displaying them. Your spreadsheet shows data every two tenths of a second. This may be great for lab rats hungry for data or others keen to see this but I find this a bit overwhelming to determine any radical change occurring such as an error code with the OBD II system capturing only a moment with data.

I don't believe the throttle body is faulty. Something, a sensor/vacuum leak/intermittent connection/whatever, is misleading the ecm to command a higher rpm.

Do you have a reader or scantool capable of capturing freeze frame data?
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Old 05-04-2021, 09:31 PM   #7
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Default Re: High idle when car is warm

For me at least, both links open your no coolant temp spreadsheet. I don't think it matters though. I don't think your problem is caused by coolant temp.
Some things I see in your data:
You throttle position matches the RPM. I proved that by taking readings from my Aura XE with 3.5L. If I press the gas pedal to open my throttle to ~31% I get similar RPM to what you recorded. Therefore it seems your throttle body is being commanded to that position and RPM.
My commanded and indicated throttle actuator positions match, yours don't.
At a normal idle (650rpm), my desired and indicated TP angle% are around 12%.
With my foot off the pedal, my accelerator position reads 0.50%. Yours reads much higher. If I depress my gas pedal to get ~10% accelerator pedal position I get a similar RPM and throttle position sensor reading and your are getting.
Based on all of that, I'm leaning towards your issue being the accelerator pedal position sensor.

With the key to on, engine not running, read the accelerator position with your foot all the way to the floor. Mine reads 100.48% when I do that and 0.5% with foot off. I would think yours should too.


Looking at a pic of the sensor on Rockauto, it looks like it might be adjustable. There may be 2 screws that can be loosened and the sensor can then be rotated while you are watching the reading and turn it to bring the reading back down to close to 0% with no pressure applied to the pedal, then tighten it. Since your reading is stable, it would be worth trying that before buying a replacement. Mark your starting position so you can get it back where it was, just in case.

https://www.rockauto.com/en/moreinfo...sn=877&jsn=877

Edit:
If you have adjustable pedals, there will be a motor on the pedal assembly, don't mess with it.
...
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2000 Saturn SL1 1.9L SOHC (Retired)

Last edited by imaddicted2u; 05-04-2021 at 09:38 PM.
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Old 05-05-2021, 08:54 AM   #8
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2008 AURA XE
Default Re: High idle when car is warm

A couple of more thoughts...
The throttle minimum relearn and diagnostics may not be allowed to run when the indicated accelerator pedal is above a certain value.
The ECM's Throttle Actuator Control (TAC) program may ignore the accelerator pedal position until the vehicle warms up OR if the pedal gets depressed. This may explain why things appear somewhat normal until you press on the gas.
Before trying adjustments, make sure your gas pedal is not stuck on a bit.
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Old 05-05-2021, 09:17 AM   #9
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Default Re: High idle when car is warm

Thank you all for your assistance. I'm going to call this issue solved for now. I am now getting idle speeds in the 600-700 rpm range after warmup.

I followed the procedure shown on this site. I don't know how authoritative it is, but it seemed to help. After several excursions above 44 mph, the idle was down to around 1700 from 2300 rpm.

During one of these drives I finally got at DTC code of P0507 "Idle Control System RPM - Higher than expected". I had not gotten any codes previously. I looked again for vacuum leaks and did not find any. I even vacuum tested the brake booster.

The other recommended action for this code was to clean the MAF sensor. This seemed help a lot, and after a couple more drives the idle now seems to be behaving as expected.

Quote:
Originally Posted by imaddicted2u View Post
I'm leaning towards your issue being the accelerator pedal position sensor.
The APP always returns to the same place when I take my foot off. I've also always been able to get normal idle sometimes (like immediately after initial warmup). So I'm inclined to think that the APP is either ok or not bad enough to cause a problem. In any event things seem to be working now, so I'm not going to mess with it.
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Old 05-05-2021, 10:26 AM   #10
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2008 AURA XE
Default Re: High idle when car is warm

You may be right but the APP is supposed to be 0 to 100%. In any event, if it's working to your satisfaction, don't fix it.
...
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