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Old 10-02-2016, 08:58 PM   #1
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Default High Idle with my 97 LSS

I have a 97 Oldsmobile LSS with 110k (no supercharger) that has a check engine light for high idle. The code that keeps appearing is p0507 for high idle which makes sense because it constantly runs at 1500 rpm when in park or at red lights.

I started with replacing plugs and wires and air filter (AC Delco). I then cleaned the MAF (used MAF cleaner) and replaced a coolant sensor.

I used the various methods I have read about to diagnose and find engine vacuum leaks (I tried both water and propane methods) and found none. I even clamped off the single vacuum hose that goes to the hvac control flaps to make sure it was not giving a problem.

I borrowed a innova code reader and have reset the code but it continues to return.
One odd think that I found was that the fuel trims vary from -10 to -20 and do not seem to change much when I move up in rpms.
Any advice?
What should be my next move?
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Old 10-03-2016, 08:04 AM   #2
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You probably have a problem with your IAC (Idle Air Control). Do a search for your problem code and you will get pointed in the right direction.
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Old 10-03-2016, 11:46 PM   #3
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I agree....high idle is usually caused by vac leak, bad IAC, dirty throttle plate sticking, cruise cable, etc.
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Old 10-04-2016, 04:29 PM   #4
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Did you ever remove the TPS sensor from the throttle body?
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Old 10-05-2016, 03:34 PM   #5
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Check range of TPS.
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Old 10-06-2016, 07:48 PM   #6
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Thanks for the replies.

Last night I disconnected the cruise control wire at the point where the cable and the accelerator cable attach. The idle continued at 1500 while the engine was at both cold and hot.


GrandpaBuick and Mike both mentioned the TPS. I have never removed the TPS. Should I remove it and inspect? I will search for instructions on how to test the range.
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Old 10-07-2016, 12:12 AM   #7
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Rare for it to be the TPS, although I must admit I did find it to be the problem once, but it was accompanied by a TPS code....you can back probe the tps to get readings......they should increase steadily from 0.4-0.5 volts up to 4.5 volts....if the closed throttle reading is much higher than 0.4-0.5 volts, that is your problem....

Most techs, have a manual IAC tool....you remove the IAC harness, insert the tool harness, which is powered by battery clips....then you have a switch that opens/closes the pintle of the IAC......if you can control the Idle with the tool, then you either have a problem with the harness/wiring or the ECM or data to the ECM(like the TPS data, CTS data, etc.)

If you can't control the idle with the tool, you need an IAC....
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Old 10-07-2016, 05:28 PM   #8
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I asked if he removed the TPS is because most people don't realize you have to reinstall it in a specific way, otherwise, your engine will run like crap.
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Old 10-08-2016, 12:31 PM   #9
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I removed the tps and put it back on again and it actually idled higher (2500-3000 rpm instead of the 1500 it had been doing). I realized that I installed it wrong and followed the instructions I found by user Danthurs on this forum. The idle returned to 1500.

I am not sure what my next move is but TechII'* suggestion to use an IAC tool is a good one. I will ask around to see if I can find one.
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Old 10-08-2016, 01:43 PM   #10
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have we pushed the throttle linkage to make sure its closed? visually look also

is it actually idle fast or just the tackometer showing 1500rpm?
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