Question about 1991 Buick LeSabre

8 Answers

1991 Buick LeSabre,wont return to idle frequently list of new parts include ecm,coolant temp sensor tps cleaned egr&iac also will idle at 15-1800 rpm switch off&restart &it idles like it should what causes this ?

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  • timhockaday Jul 31, 2009

    this car does not have electronic climate control

  • timhockaday Jul 31, 2009

    No trouble codes set, when problems first occured code 26 showed on diag. test, replaced purge canister solenoid,tps,coolant temp sensor,cleaned egr,&iac valve (not sure how to test iac for working cond. though)also installed new 02 sensor and reman ecm. trans fluid/filter will be changed first of coming week did have bad drivability problems but this rash of parts I threw at the car has almost fixed the problem if I could get it to idle down. this occurs on a frequent basis and will sometimes correct itself.

  • timhockaday Jul 31, 2009

    Car seems to have idle speed issue hot or cold when it does this sometimes it will correct itself but you can switch off and immediately restart and it will idle as it should but you can drive again and stop and engine will hi idle. have driven 20 mi at 70mph after reconnecting battery this makes no difference

  • timhockaday Jul 31, 2009

    have replaced pcv valve and already hunted for any vacuum leaks could fuel pressure reg be a possible culprit? because as soon as you turn off engine and residual vac leaves restart and it idles fine. am going to clear memory on pcm and try to let it relearn a new home as well.

  • timhockaday Jul 31, 2009

    well if map/maf sensor is bad how will i check this? my prior exp is if map/maf is bad car might run but any related given symptoms will be constant,not intermittent. havent seen one of these go half-way bad. has anyone else?

  • timhockaday Jul 31, 2009

    I need to know how to check iac for proper operation on this 91 lesabre anyone know the correct steps to take?

  • timhockaday Jul 31, 2009

    to last inquiry car does not stall. it is iac solenoid.fount my old orig gm shop manual (thought i'd lost it) so i've done all diagnostics and found out what the problem really is thanks for all your help,it is much appreciated!!!

  • timhockaday Aug 01, 2009

    thanks for the additional input on the situation I found the prom to be defective as well as a couple other parts also after fureher diag. testing. Thanks for your help

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8 Answers

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If you have electronic climate control try moving the lever to something other than off. I have seen on tese cars the button off position be defective. No load would allow the the car to idle high because the climate is sending false info.

Posted on Jul 31, 2009

  • Ernset ( Skip ) Bouvette

    After further study and going to a mechanics forum site and and getting insight from people from all over the word everyone stated a new computer fixed this. I see you stated you already replaced yours. Did you replace the removable prom also. Did you get a junkyard, reman, or new replacement.

    They replaced the prom also. Their symptoms were the same. Shut the car off and restart and it was fine.



    If you had a big vacuum leak which could cause this also it would not correct itself on a key cycle which leads me also to think a PCM problem. Also make sure alll fuses especially the ones that say Ignition or ECM are good. As I remember there is a fuse on some for the keep alive memory. If you loose this the computer will not retain all it has learned.

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You may want to check the timing of the engine. It could be advanced. You may need to have a timing light to get the correct timing for your car. Check if adjusting the idle control valve or fast idle control valve would help bring down the idling. If not see if cleaning it would help. Other than that you may have to have the ECU tested. If there is a spare ECU from another known working car, have it swapped for a while to see if it is on the ECU or on the engine. Even faulty wiring can be a cause of this issue.

Posted on Jul 31, 2009

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I don't quiet understand your question, Im guessing that the engine run as long you keep it above 1500 to 1800 rpm and when let off the gas pedal the engine drop below idle and quit or dies. Being 1991, if you have high miles thing you can do.
1 clean throttle body with pray cleaner while engine off and running
2 check plugs make sure they all good and have proper gap
3 check air flow mass sensor, if you need to replace it get one from the
junk yard for cheap.
4 some of your injectors may be clog, run high test 93 and mix it with
fuel injector cleaners, if that don't work, you may have to replace it.
5. Hope this is not the problems, Cam Sensor going bad or
sensor may be covered up with dirt, grease, and grimes its a pain to
replace.

Posted on Jul 31, 2009

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Idle air control valve/ swithch. Its a small little unit on the side of the throttle body itself. It control the amount of air needed for idle by the PCM.

Posted on Jul 31, 2009

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Maff or map sensor would be my guess. Also check all those vacuum lines.

Posted on Jul 31, 2009

  • Nate Stansfield
    Nate Stansfield Jul 31, 2009

    leaky vacuum hose, faulty pcv or stuck injector.

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Engine idle is necessary for proper vehicle operation; it allows the engine to operate at the lowest RPM level possible without your foot on the gas pedal. At idle, your engine produces the least amount of emissions than in any other time it is operation. Even when your key is in the off position the vehicle still utilizes electrical power from the battery. The amount of electrical power used is a very small amount; the battery can sustain this usage for many weeks. But, when electrical power is completely removed from the system the natural memory is erased. This natural memory is a result of an accumulative data that has been processed and learned by the ECM/PCM. One of the natural memory events is the engine idle speed. When the car battery is dead or replaced or, if you have swapped the engine CPU, this natural engine idle speed is lost. After the battery is replaced or charged the engine idle will need to re-learn itself, this is normal. In some instances this re-learn procedure is un-noticeable while others are quite noticeable. During the idle-relearn period the engine will stall when in idle mode, but it is not unheard of too idle to high also. Use the steps below to address your issue.

Step 1 - Engine idle low or stall: Once the new battery is installed or charged start the engine. When the engine try's to stall hold your foot on the gas pedal just a little to aid the idle speed. You will need to continue doing this until the engine is warm. When the engine is at operating temperature the basic engine idle setting will engage, the engine should re-gain idle properties. If the engine is still not responding a short drive is sometimes required, both feet will be used to perform this procedure. Put one foot on the throttle and the other on the brake pedal. Continue this until basic engine idle is achieved

Step 2 - Engine idle to high: Once the new battery is installed or charged start the engine. Start the engine and allow to warm up to operating temperature. As the engine warms the engine idle should return to normal. If the engine does not return to idle a short drive will be needed. (Note: if engine idle is extreme do not attempt this step). Drive the car until normal engine speed is engaged

Posted on Jul 31, 2009

  • Michael Masters
    Michael Masters Jul 31, 2009

    If this has already been tried, I would move to the PVC valve and hose. this valve May be clogged or the hose may have collapsed. inspect and replace if needed.

    Another issue could be a bad vacuum connection or leaking vac hose. Check all vac hoses leading to the IAC and Coolant cavity as well. I will post a Minimal idle speed manual adjustment procedure below. follow carefully to manually adjust the idle.




    1. Using an awl, pierce the idle stop screw plug (located on the
      side of the throttle body) and remove it by prying it from the housing.



    2. Using a jumper wire, ground the diagnostic lead of the IAC motor.


    3. Turn on the ignition, DO NOT start the engine and wait for 30
      seconds, then disconnect the IAC electrical connector. Remove the
      diagnostic lead ground lead and start the engine. Allow the system to
      go to closed loop.



    4. Adjust the idle set screw to 550 rpm for the automatic transaxle (in Drive) or 650 rpm for the manual transaxle (in Neutral).



    5. Turn the ignition
      OFF
      and reconnect the IAC motor lead.



    6. Using a voltmeter, adjust the TPS to 0.45-0.65 volt and secure the TPS.


    7. Recheck the setting, then start the engine and check for proper idle operation.


    8. Seal the idle stop screw with silicone sealer.



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Has the car been driven over 45mph for a least 5 miles since the ECM and was replaced or the IAC was cleaned? And does the rpms idle high after a warm restart, say you park the car, go into a store for 10 minutes or so, get in your car and start it. Does the idle go high then?
Is the service engine soon light stay on at times?

I would start by disconnecting the battery for 15 minutes, reconnect the battery and drive the car above 45 mph for a least 5 miles.
Disconnecting the battery will reset the ECM to default status and driving the vehicle above 45 mph for 5 + miles will allow the IAC to relearn its "home" position.
If it is occurring only after a cold start, first time it has been started that day, I would suspect and EVAP issue causing an air leak.
Let me know.
Regards,

Posted on Jul 31, 2009

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When was the last time you changed the transmission oil and the filter? Sometimes bad transmission fluid will cause this. Its pretty simple to do. Also have you tried reading trouble codes at all? Let me know how this turns out.


Benjamin

Posted on Jul 31, 2009

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