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High idle and snappy throttle after full throttle acceleration 850 1994

posted by  adrian on  Mon Nov 15 12:56 CST 2010
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last visit: Sun Jul 21 12:55 CST 2013
[RELATED]

Hi all,

I'm kind of stumped with this one. I recently aquired a 1994 850 5 speed Volvo. When driving normally (light footed, moderate acceleration) the engine runs great. No problems at all. But when I press the accelerator to the floor to merge onto a highway, the throttle is very snappy from accel to decel and vice versa. Once off the highway and at a stop light or stop sign, the car idles high (~1500 rpm or higher) and does this until I turn the car off for more than 20 seconds or so. Once I start it up, the engine idles fine and throttle response is normal again - not snappy.
This leads me to believe there is something electronic that i'm triggering and it is sticking.

This weekend I did a lot of troubleshooting. I have done the following...

- Cleaned IAC and tested with known good one. Problem still exists.
- Tested TPS simply by unplugging it. Got the typical backfire on decel so i'm assuming its good. Problem still exists.
- Replaced oxygen sensor and fixed vacuum leaks. Problem still exists.
- Removed intake manifold to clean out and clean/test egr valve. Bought a vacuum pump and tested egr - held vacuum quite well and was fairly clean. Cleaned intake, egr, flame trap and throttle body. Problem still exists.

I'm kind of stumped now. I tested the vacuum solenoid going to the egr valve and it holds vacuum. After a significant amount of reading on turbobricks, brickboard and my chilton manual, I feel it has something to do with the egr system but I just can't pinpoint it.

Any help on this matter would be fantastic as i'm at my wits end with this thing.

Thanks a bunch,

Adrian








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    High idle and snappy throttle after full throttle acceleration 850 1994

    posted by  mbliss on  Tue Nov 16 08:28 CST 2010
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    last visit: Tue Oct 21 20:49 CST 2014
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    I don't know anything about EGR systems, but I would think that would set a code. Sure sounds like a mechanical problem with the throttle, though. With the engine off, have you tried stomping on the accelerator and checking for proper return action?

    --
    '96 850T and '83 244 DL both at about 200K, '97 850T5; gone but not forgotten '81 245 and '64 Amazon








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      High idle and snappy throttle after full throttle acceleration 850 1994

      posted by  adrian on  Tue Nov 16 14:46 CST 2010
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      last visit: Sun Jul 21 12:55 CST 2013
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      I tried this several times - both with the car running (just a quick snap of the throttle to see if the idle would change) and with the engine off. No difference though...the problem is still there.

      I cleared the codes last week. I will check again tomorrow to see if any have been stored.








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    High idle and snappy throttle after full throttle acceleration 850 1994

    posted by  someone claiming to be fixit2002 on  Tue Nov 16 02:24 CST 2010 [RELATED]

    Maybe check the air filter box thermostat. Alot of them go bad and fail always with the heated air intake stuck open. If this happens the MAS may be getting a blast of hot air when you accelerate and upsetting the output. They can be removed and the air control vain wedged to not allow heated air.








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      High idle and snappy throttle after full throttle acceleration 850 1994

      posted by  adrian on  Tue Nov 16 14:42 CST 2010
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      last visit: Sun Jul 21 12:55 CST 2013
      [RELATED]

      I checked the air box thermostat and it seems to be working. Just in case it wasn't, I removed it. The problem still exists.








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        High idle and snappy throttle after full throttle acceleration 850 1994

        posted by  someone claiming to be fixit2002 on  Wed Nov 17 02:06 CST 2010 [RELATED]

        Have you tried just disconnecting the battery for 15 minutes to reset the fuel table settings?








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          High idle and snappy throttle after full throttle acceleration 850 1994

          posted by  adrian on  Wed Nov 17 05:07 CST 2010
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          last visit: Sun Jul 21 12:55 CST 2013
          [RELATED]

          Tried this today and there is no difference. The car ran rough for a little bit and eventually smoothed out. I am going to try blocking the egr pipe at the header.







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