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Hesitation at tip-in 700

posted by  LoveMy240Wagon on  Wed Jan 7 14:11 CST 2015
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last visit: Tue Dec 31 09:52 CST 2013
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Hi, I'm still having some issues with my '92 740 which seem to be related to cold, or at least loosely related.

The car will be idling fine and then as soon as I depress the gas pedal, even just slightly, RPM's drop fast, it nearly stalls out. If I continue pressing the gas pedal the engine barely runs, nearly dies, bucks and kicks, I would swear it's running rich but I don't really know. Then I let off the gas and after running at very low RPM for a few seconds the engine will recover and run fine. To avoid all this I have learned to let off the gas when it first hesitates, RPM's recover quickly, then I can give it gas and go. This all happens in a matter of a second or two, the car behind me at a light never notices the hesitation. This problem seems to be worse when the car is cold and it is VERY cold out right now. After driving for a few minutes the issue gets much more infrequent but never goes away completely.


I checked the function of the TPS but I did not check it with a meter. Throttle body was just cleaned and the ECT was replaced recently although I suppose I should check it anyhow. The rubber intake boot is in good condition with no leaks. No codes.

Any ideas for me?
--
'89 240 wagon, '90 740 sedan, '92 740 wagon








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    Hesitation at tip-in 700

    posted by  LoveMy240Wagon on  Tue Jan 27 21:29 CST 2015
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    last visit: Tue Dec 31 09:52 CST 2013
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    Well it turned out to be the ECT (Engine Coolant Temp) sensor.

    I eventually got a 2-2-4 code from the OBD.

    The sensor is for the computer and it is on the driver side of the block towards the back, the one that's really hard to get at! The sensor that is easy to reach in the front is for the dash gage I believe.

    I didn't take off the intake manifold, just the clean air tube going to the throttle body and the Idle Air Bypass valve to give me some room to work.

    Only lost a cup of coolant in the process and didn't take longer than 45 minutes from start to finish.

    Thanks for the help!
    --
    '89 240 wagon, '90 740 sedan, '92 740 wagon








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    Hesitation at tip-in 700

    posted by  Milanomike on  Wed Jan 7 18:42 CST 2015
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    last visit: Sat Oct 11 22:27 CST 2014
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    If it does the hesitation all the time, I'd run thru the throttle position adjustment routine, it needs to be spot on. When you press the accelerator, the TPS clicks, which tells the ECU you want to go. If out of adjustment, you will get the stumble. Also, check for vacuum leaks. Finally, if intermittent as happened on my 93 once, I'd check the crank position sensor for fraying cover/insulation. This turned out to be an intermittent hesitation I'd get from time to time. Again, if it always does, check TPS adjustment. Also verify TPS works all the time. Good luck.








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    Hesitation at tip-in 700

    uid 46171's pic
    posted by  kittysgreyvolvo on  Wed Jan 7 15:01 CST 2015
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    last visit: Sat Oct 18 15:23 CST 2014
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    Your 1992 740-series Volvo, I'm rather certain, includes OBD-1 diagnostic function.

    https://www.brickboard.com/FAQ/700-900/EngineOBDCodes.htm

    Throttle Position Sensor can fail at any time.

    Do own a multimeter? How did you verify TPS function? By ear? Continuity, or unwanted conductivity, can happen no matter the symptoms heard.

    Id suggest you available yourself to the many article in the FAQ.

    https://www.brickboard.com/FAQ/700-900/

    - Fuel Injection System Relay (reflow all broken solder welds)
    - Air intake system leak downstream of the air filter, inclusive of all vacuum lines and duting.
    - Faulty Wire Harness or Faulty Wire Harness Connector.
    - Faulty coolant temperature sensor.
    - The need for a tuneup. (Rotor, dist. cap, spark plugs or correct spark plug gap, air filter).
    - Faulty EVAP

    And more ....

    Please diagnose your 740 for fault conditions.

    Report results here to your thread.

    Brickboard members shall reply with diagnostic suggestions and perhaps a solution.

    Questions?

    cheers,

    Mac Cheesed Duff.








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      Hesitation at tip-in 700

      posted by  LoveMy240Wagon on  Wed Jan 7 17:21 CST 2015
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      last visit: Tue Dec 31 09:52 CST 2013
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      Thanks for the tip but OBD is showing all clear, no codes.

      I only verified that the TPS was clicking and doing so when the accelerator is depressed. I figured that if the TPS had completely failed I would have bigger problems than this and given that it seems temperature related I was giving the TPS a low probability.

      The FAQ is great and I use it often, I was hoping someone with a similar experience might be able to narrow it down a bit from the all inclusive list of potential failures.

      --
      '89 240 wagon, '90 740 sedan, '92 740 wagon







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