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Intermittent High Idle Speeds


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Donald, Thanks for reporting back! Your confirmation will surely help others in the future.

_____________________________________________________________________________________________________________________

BodybyFisher, I agree, I almost replaced the PCM, the TPS was the last component on the input side of the PCM that could cause an idle concern. Below is a list of TPS codes and the conditions for setting that code. My SWAG is that the TPS is failing with a calibrated range, most likly voltage spiking, it's odd that none of them set. The PCM thought the TPS input was legit and commanded the IAC according to the errononeus input from the TPS.

  • P0120 = TP Sensor Performance- MAP signal changes 3 kPa or less in .21 seconds following a 5 degree or greater INCREASE in throttle angle. OR. The MAP signal changes 2.2 kPa or less in .21 seconds following a 4.7 degree or greater DECREASE in throttle angle.
  • P0121 = TP Sensor Circuit Insufficient Activity - The throttle position sensor input is not within its expected range.
  • P0122 = TP sensor voltage too low.-The TP sensor reading is 0.1 volts or less
  • P1121 = TP Sensor Circuit Intermittent High Voltage - Throttle position 4.96 volts or greater.
  • P1122 = TP Sensor Circuit Intermittent Low Voltage - Throttle position 0.1 volts or less

Regards, Frank

Edited by Frank T
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  • 3 weeks later...

I'm having the same problem on a 2003 Deville Northstar. It's been going on for a couple of years with no mechanic work successful. The TPS has been replaced at least once. The throttle body has been cleaned.

The engine idles normally at about 650 rpm some of the time. Then it picks up to 1400-1800rpm while in neutral and, it seems, when in gear and running along at low enough speeds to notice.

There had been a vacuum leak but it's now been days since that got fixed. I'm told there are no codes.

Also: It seems to be running a bit erratically at low speeds (20-25mph).

Also: "Passing gear" downshift at 45-55mph is intermittent. Sometimes it works and sometimes not. When it doesn't then it won't return to normal during that trip or day. Maybe better early in the trip?

Also: lately I've noticed there's a mild hesitation when starting off from a dead stop.

I'm thinking that if the rpm issue is fixed then maybe some of these other things will get fixed as well.... ?

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is your air pump running excessively. (by air pump I mean the emissions pump)that raises the idle

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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I have the same problem on a 2003 Deville Northstar. The TPS has been replaced and the throttle body cleaned. No change. No codes. What should I be looking at next?

If you have access to a scan tool, then look very carfully at the data stream while the problem is occurring, you may be able to pinpoint the problem. Follow these steps:

  1. Look very closely at all of the inputs to the PCM that control idle speeds. I have them listed in a previous post.
  2. If all the inputs including the "TPS at idle" paramerter (it should say YES when the throttle is at idle) are normal, and the PCM is NOT commanding a high idle, ( IAC counts are at approx 650) I would suspect a sticking IAC valve.
  3. If the PCM is commanding the high idle, I suspect the TPS or PCM.
  4. Observe the IAC counts while the problem is occuring, it should be around 650 counts, if its higher than 650 counts, and the TPS you installed is an aftermarket piece, I would replace it again with an OEM part.
  5. Make sure the connections at the TPS and PCM are clean and tight, last resort would be faulty PCM.

Good luck, it took me seven months to figure out my high idle concern.

Regards, Frank

Edited by Frank T
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  • 1 year later...

Frank thank u so much for posting an being so clear, wow I cant believe I found someone in my same situation. My high idle started all of a sudden so I took it to mechanic suppose to be master mechanic, they say it was the throttle air intake control valve so they replaced it an that worked it got the motor from 2400 rpm to 740rpm great but I went home parked for one hr came out cranked up it went back to 2400rpm so I took it back it was late so the mechanic waited until tomorrow to check he said he cranked up an he found no problem so I came an picked up car an he was rite car was at 750 rpm but got home an again 1hr later back up to 2400rpm so he says he thinks its the motor mount wich broke in the process of all of this high idle, he thinks that when the motor moves its disrupt ing the ground

wires some were, because wen I was troubleshooting the car before I took it to the mechanic I changed the tps cleaned throttle body checked for leaks by spraying intake cleaner around intake an listening for changes in the sound of the motor if the motor was suckin it would have picked up some of the throttle cleaner an raised the motor, I never checked the mas air intake sensor but the mechanic changed the air contol throttle so we chaged everything, an still having these how u say intermitted episodes, wow gonna run me crazy, so I checked everything again all wires connectors cleaned intake again an this time bought a new mas intake sensor I unplugged everything I could an checked for corrosion an cleaned an put back craked car back to 750rpms how long I dont no???? THIS IS SO NERVE RECKIN TO ME. im scared to drive it cause after all the money I spent it still might go back to a high idle but I will wait till tomorrow to crank an se if the new mas air intake sensor works its for a 2000 cadillac deville. Please excuse my long rant but I thought I was the only one with this intermittent problem, also I need to add that wen I got the car back from mechanic the first time it ran at 750rpm but when I would put it in drive or park it would have a terrible jerk I mean really strong jerk front wards or backwards he blamed it on the motor mount witch I thought that even with a bad motor mount the jerk was to strong, ok so I took the car back to him because of the returning high idle an wen I picked it up with a 750rpm the same rpm almost no jerk forward or backward a nice smooth shift but got home cut car off an high idle an strong jerk returned, so I just changed the mas flow air intake an cleaned all again cranked up with a good low idle 750rpm an a smoot shift no strong jerk I will keep u posted to see if the mas air flow intake sensor solved the problem, im so glad that these kinds of sites are here for us to exchange our knowledge thanks everyone for taking the time any thoughts would b appreciated.

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dstone: The first thing to do is to run the OBD codes. You can do it from the A/C buttons. With the key on, press <Off> and <Pass Warmer> together for a few seconds until all the dash lights come on like you just turned on the key, then release both buttons. The car's computer will poll each of the computer modules in the car and report their OBD trouble codes on the driver information center below the speedometer. Write them down and post them back here.

The list will end with the prompt "PCM?" You can turn off the key, or press AUTO (push the A/C temperature knob in). If you miss a code, or want to re-run the codes to check your list, press <Off> and the code list will repeat.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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I have a 2000 deville I dont see a pass 2 warmer I have pass temp up/down then pass off button , the the round off button that can be turned for temp control, I tryed a few sequences withe nothing could u be more Pacific with what I have on how to run obd, I did run a obd with the top left set of buttons the on/off , info/rest, an info buttons but there not on ac bored so I an guessing that is two different obd is that true.THANKS IN ADVANCE.

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Use the Pass Temp Up button with the main <Off> button that is the on/off button.

Sorry for the confusion. I had only one model that worked that way, and the exact terminology of the buttons changes with the model and the year.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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  • 2 weeks later...

Frank thank u so much for posting an being so clear, wow I cant believe I found someone in my same situation. My high idle started all of a sudden so I took it to mechanic suppose to be master mechanic, they say it was the throttle air intake control valve so they replaced it an that worked it got the motor from 2400 rpm to 740rpm great but I went home parked for one hr came out cranked up it went back to 2400rpm so I took it back it was late so the mechanic waited until tomorrow to check he said he cranked up an he found no problem so I came an picked up car an he was rite car was at 750 rpm but got home an again 1hr later back up to 2400rpm so he says he thinks its the motor mount wich broke in the process of all of this high idle, he thinks that when the motor moves its disrupt ing the ground

wires some were, because wen I was troubleshooting the car before I took it to the mechanic I changed the tps cleaned throttle body checked for leaks by spraying intake cleaner around intake an listening for changes in the sound of the motor if the motor was suckin it would have picked up some of the throttle cleaner an raised the motor, I never checked the mas air intake sensor but the mechanic changed the air contol throttle so we chaged everything, an still having these how u say intermitted episodes, wow gonna run me crazy, so I checked everything again all wires connectors cleaned intake again an this time bought a new mas intake sensor I unplugged everything I could an checked for corrosion an cleaned an put back craked car back to 750rpms how long I dont no???? THIS IS SO NERVE RECKIN TO ME. im scared to drive it cause after all the money I spent it still might go back to a high idle but I will wait till tomorrow to crank an se if the new mas air intake sensor works its for a 2000 cadillac deville. Please excuse my long rant but I thought I was the only one with this intermittent problem, also I need to add that wen I got the car back from mechanic the first time it ran at 750rpm but when I would put it in drive or park it would have a terrible jerk I mean really strong jerk front wards or backwards he blamed it on the motor mount witch I thought that even with a bad motor mount the jerk was to strong, ok so I took the car back to him because of the returning high idle an wen I picked it up with a 750rpm the same rpm almost no jerk forward or backward a nice smooth shift but got home cut car off an high idle an strong jerk returned, so I just changed the mas flow air intake an cleaned all again cranked up with a good low idle 750rpm an a smoot shift no strong jerk I will keep u posted to see if the mas air flow intake sensor solved the problem, im so glad that these kinds of sites are here for us to exchange our knowledge thanks everyone for taking the time any thoughts would b appreciated.

dstone,

Thanks for the reply, and I'm glad I was able to help another Caddy owner. I never got a code, but, the throttle position sensor is what fixed my car, 215,000+ miles and still going. FrankT

Edited by Frank T
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What he said. If there are no Pnnnn codes, look at the throttle position sensor and the idle speed stepping motor.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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2000+ Devilles use the ON/OFF and INFO UP buttons. When ALL? appears on the information center, press the ON/OFF button and the codes will be displayed.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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2000+ Devilles use the ON/OFF and INFO UP buttons. When ALL? appears on the information center, press the ON/OFF button and the codes will be displayed.

Yes you are correct, just like my 99, I have to press the two outer buttons (up/down and on/off) simultaneously to start the self-tests, then the DIC will scroll through the modules and display DTCs, if any are active or stored.

Edited by Frank T
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  • 2 years later...

:welcomesmiley:

The 1994 Fleetwood uses the 350 cid iron V8, regular gas and 260 hp. Can you run the OBD codes? If there is an electrical problem that should tell the tale. If there are no codes, a sticking ISC stepping motor is probably the cause.

Don't replace the PCM just yet. It's expensive and requires a dealer with a Tech II to program it and make it work. Modules themselves almost never go bad in Cadillacs unless you hook jumpers up backwards with a dead battery or get ham-fisted with the wiring harness.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Fleetwood Diagnostics:

Simultaneously press and hold the OFF and WARMER side of the temp rocker. After the segment check, -00 will be displayed. That is the "pointer". Pressing OUTSIDE TEMP will toggle between the pointer and the trouble code. Use the FAN UP/DN to increment/decrement the pointer.

Pointers -00 thru -04 contain the trouble codes. Current codes are two digits and history codes have three digits with a "1" as the first digit. The second and third digits are the trouble code. For example 32 would be a current code and 132 would be the same code although a history code.

Pointer # Parameter Display Range Default value

-00 ECM Trouble Codes

-01 CCM Trouble codes

-02 ECC Trouble codes

-03 SIR (Airbag) trouble Codes

-04 ABS/TCS Trouble Codes

-05 Program number 0-255

-06 Commanded blower motor spd 0-128

-12 Vehicle speed in MPH

-16 Sun load sensor assy 200+ = Dark 240

150- = light

-17 Current temp. valve position 0-255

-19 Temp valve pos. (full hot) 180-250 180

-20 Temp valve pos. (full cold) 5-60 60

-21 Coolant temperature degrees C 90

-22 Commanded temp valve pos. 0-255

-24 Air delivery mode 0-7

-25 Inside air temp sens Value increases as temp. decreases

-28 Outside air temp asm Value increases as temp. decreases

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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  • 3 weeks later...

Check for vacuum leaks on the LT1. Pcv tube tears and leaks, you might also have a pcm code for a lean oxygen on bank 1.

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  • 3 years later...

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