Slow returning to Idle? - Cadillac XLR Forum: XLR and XLR-V Forums
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post #1 of 20 (permalink) Old 03-28-2010, 11:02 AM Thread Starter
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Slow returning to Idle?

Has anyone experienced a very slow or lazy return to idle (800 or so RPM). After removing my foot from the accelerator the idle will solwly drop to about 1200-1300 RPM and stay there until I come to a complete stop. I can hear and feel the transmission flaring as it downshifts which is usually a symptom of high idle. Is there an aux air or idle valve that might be sticking or dirty. The local dealer tech says its "normal", I don't think so... does anyone have experience with this condition in a V,
Thanks,
Bill
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post #2 of 20 (permalink) Old 03-28-2010, 12:59 PM
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Originally Posted by BILLS_XLR View Post
Has anyone experienced a very slow or lazy return to idle (800 or so RPM). After removing my foot from the accelerator the idle will solwly drop to about 1200-1300 RPM and stay there until I come to a complete stop. I can hear and feel the transmission flaring as it downshifts which is usually a symptom of high idle. Is there an aux air or idle valve that might be sticking or dirty. The local dealer tech says its "normal", I don't think so... does anyone have experience with this condition in a V,
Thanks,
Bill
How many miles?
What condition is the battery in?
A dirty throttle body can cause mild sticking of the butterfly valve, if so easy to clean.
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post #3 of 20 (permalink) Old 03-28-2010, 01:02 PM
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post #4 of 20 (permalink) Old 03-28-2010, 02:52 PM
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I think some WD-40 in the right place will fix this issue.
Ah - where? These cars have an electronic throttle, so there is no cable to lubricate? Just the throttle body motor?

Just curious as to where you were thinking of applying it. I would avoid WD-40 anyway, but that is more of a personal thing. I do use the stuff for some applications, true, but prefer to use the correct lubricant if I am lubricating a specific item.
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post #5 of 20 (permalink) Old 03-28-2010, 03:17 PM Thread Starter
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How many miles?
What condition is the battery in?
A dirty throttle body can cause mild sticking of the butterfly valve, if so easy to clean.
28K.... New 2 months ago....
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post #6 of 20 (permalink) Old 03-28-2010, 03:24 PM
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28K.... New 2 months ago....
OK. Shouldn't be either of those then, however I was thinking of a possible low battery condition holding the revs up to aid recharging. I would have a close look at the throttle body. Occasionally throttle body motors do fail (this is a general observation, not specifically XLR related).

Last edited by xlrlist01; 03-28-2010 at 03:36 PM.
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post #7 of 20 (permalink) Old 03-28-2010, 03:38 PM Thread Starter
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OK. Shouldn't be either of those then, however I was thinking of a possible low battery condition holding the revs up to aid recharging. I would have a close look at the throttle body. Occasionally throttle body motors do fail (this is a general observation not XLR related).
LIST,
Thanks That's where I'm going to start...I've ordered the repair manuals but they haven't arrived. Do you know if there is any kind of Auxiliary air supply valve where it might be located?
Thanks,
Bill
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post #8 of 20 (permalink) Old 03-28-2010, 03:45 PM
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LIST,
Thanks That's where I'm going to start...I've ordered the repair manuals but they haven't arrived. Do you know if there is any kind of Auxiliary air supply valve where it might be located?
Thanks,
Bill
I don't think so. All the best!
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post #9 of 20 (permalink) Old 04-09-2010, 08:14 AM Thread Starter
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I don't think so. All the best!
Cleaned the throttle body, which is quite an adventure. Condition still exists!!
Has any one experienced a hesitiation about 1500 RPM when decellerating. My throttle holds at 1200 while decelerating, with or without taping the brakes, with or without the AC on and with leaving it in drive or shifting to neutral. As soon as the speed (speed signal) goes to 0 the idle drops to 800 or so. Something is reading the 0 speed signal and dropping the idle. I have thoroughly cleaned the throttle body (that's another story) and checked for vacumn leaks with none found. The local dealer said this is normal on supercharged cars but I don't buy it! There may be some slight compensation for the additional air volume when the throttle first closes but but I don't think it should "high idle" all the way down to 0 MPH. Its definately effecting Gas mileage, brake wear and It could be considered a safety issue as simply llifting off the throttle does not generate anywhere near the engine braking effect that you would expect.
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post #10 of 20 (permalink) Old 04-09-2010, 09:44 AM
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Has your dealer run diagnostics with a Tech 2?

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post #11 of 20 (permalink) Old 04-09-2010, 02:46 PM
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Cleaned the throttle body, which is quite an adventure. [snip] llifting off the throttle does not generate anywhere near the engine braking effect that you would expect.
What is the throttle reading (actual and commanded) with your foot lifted off the throttle pedal? You will need a Tech-2 for this. Sometimes the position feedback fails and can cause odd behaviors. (This is a generic observation.)
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post #12 of 20 (permalink) Old 04-09-2010, 03:02 PM Thread Starter
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Has your dealer run diagnostics with a Tech 2?

CC
CC I brought it in for the idle issue and a nonfunctioning exhaust sound baffel(it was stuck on LOUD). The service advisor said the tech didn't find any codes and test drove it and found it "normal" for supercharged cars. I believe that he had to hook up Tech2 to get the diagnosis for a faulty solenoid so there probably were no codes present.
LIST: You're right I'll need a Tech2 to access these readings.
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post #13 of 20 (permalink) Old 04-09-2010, 07:01 PM
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Check your service ticket and see if there is a notation by the mechanic regarding the Tech2 analysis outcome.



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post #14 of 20 (permalink) Old 04-13-2010, 02:54 PM
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Cleaned the throttle body, which is quite an adventure. Condition still exists!!
Has any one experienced a hesitiation about 1500 RPM when decellerating. My throttle holds at 1200 while decelerating, with or without taping the brakes, with or without the AC on and with leaving it in drive or shifting to neutral. As soon as the speed (speed signal) goes to 0 the idle drops to 800 or so. Something is reading the 0 speed signal and dropping the idle. I have thoroughly cleaned the throttle body (that's another story) and checked for vacumn leaks with none found. The local dealer said this is normal on supercharged cars but I don't buy it! There may be some slight compensation for the additional air volume when the throttle first closes but but I don't think it should "high idle" all the way down to 0 MPH. Its definately effecting Gas mileage, brake wear and It could be considered a safety issue as simply llifting off the throttle does not generate anywhere near the engine braking effect that you would expect.
1/ Get a comparison with another V.

2/ It is possible for a failing throttle controller unit to start to fail but not necessarily set a fault code, or it could set an obscure fault code. I diagnosed a defective throttle control unit (in a F*rd, I know ) using a fairly basic reader. By observing the actual position I could see it was making improbable jumps (because the unit's position sensor was failing) while somebody else was driving. I forget what fault code set in the end but it was a weird one. The driver symptom was sudden severe surging forward at lowish speeds or total loss of power at higher speeds. Better still the local dealer diagnosed this as 'normal' (it was mildly chipped car) but observed that the car ran very 'rough' (incredible considering that the factory program had been reinstalled while they diagnosed this driveability problem). We sent it to another dealer at that point as it was interesting that even with a car that was close to undriveable at times a dealer was capable of returning the car 'no fault found'. (Useful learning experience here.) (I might add that the dealer which solved it spent a lot of time looking at the wrong things, some faults can be less than obvious, IIRC it took about a day of labor in the end.)

It can take considerable care to investigate all the symptoms to diagnose what is wrong in modern cars, don't ever forget that the ECM does not 'know' what is wrong, it has to guess based on a combination of out of kilter readings and then set a fault code or two based on that mis-match; the absence of a code does not automatically mean everything is good either.

Last edited by xlrlist01; 04-13-2010 at 02:59 PM.
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post #15 of 20 (permalink) Old 04-15-2010, 07:04 AM Thread Starter
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1/ Get a comparison with another V.

2/ It is possible for a failing throttle controller unit to start to fail but not necessarily set a fault code, or it could set an obscure fault code. I diagnosed a defective throttle control unit (in a F*rd, I know ) using a fairly basic reader. By observing the actual position I could see it was making improbable jumps (because the unit's position sensor was failing) while somebody else was driving. I forget what fault code set in the end but it was a weird one. The driver symptom was sudden severe surging forward at lowish speeds or total loss of power at higher speeds. Better still the local dealer diagnosed this as 'normal' (it was mildly chipped car) but observed that the car ran very 'rough' (incredible considering that the factory program had been reinstalled while they diagnosed this driveability problem). We sent it to another dealer at that point as it was interesting that even with a car that was close to undriveable at times a dealer was capable of returning the car 'no fault found'. (Useful learning experience here.) (I might add that the dealer which solved it spent a lot of time looking at the wrong things, some faults can be less than obvious, IIRC it took about a day of labor in the end.)

It can take considerable care to investigate all the symptoms to diagnose what is wrong in modern cars, don't ever forget that the ECM does not 'know' what is wrong, it has to guess based on a combination of out of kilter readings and then set a fault code or two based on that mis-match; the absence of a code does not automatically mean everything is good either.
Got some feedback from a couple of other V owners and at least I'm confident of two things, 1.) this condition is not "normal" as theirs vehicles do not experience this condition and 2.) It is NOT a sticking throttle plate. I'm going to try another dealer and insist on a test drive with me demonstrating the condition. If I scare the [email protected]#% out of the tech or SA when it wont slow down as it should I think that they will "get it!".
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