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Old March 27th, 2012, 08:14 PM   #1 (permalink)
1974 DELTA 88
 
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Idle Speed (IN PARK)

I was adjusting my idle today and found that setting it to the service manual spec of 650 rpm in DRIVE ends up being around 1200-1300 rpm in PARK. Seems too high to me. This is with vacuum advance on ported vac, it was more of an extreme difference running off of manifold vac. I cannot detect any vacuum leaks.

I do like how the car feels with the 650 rpm idle in drive though, seems more responsive. My concern is the high idle in park.

What do you guys idle at in park?
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Old March 28th, 2012, 07:08 AM   #2 (permalink)
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Are you checking the RPMs with a factory tach, if so are you sure it is correct. Also what convertor do you have stock? Seems like if the RPMs drop in half, that is a big drop off.
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Old March 28th, 2012, 07:19 AM   #3 (permalink)
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Yes on manifold vacuum it will bump your idle higher, so after you switch ports you would then need to lower it and then re-adjust your air/fuel mixture.

I would think that 650 RPM, in drive, and A/C on, would usually get you around 8-850 RPM in Park. If you feel it is too high and you can get away with it, lower it to an RPM to where the car just creeps in gear with the A/C on and not stall out or run rough. Ensure your engine is completely warmed up and the choke is completely disengaged.
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Old March 28th, 2012, 09:24 AM   #4 (permalink)
1974 DELTA 88
 
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I use a tach/dwell meter to hook up under the hood while I am working.

I know manifold vacuum will cause the idle to be much higher in park as the vacuum is higher and pulling more vacuum advance in park, but I was amazed how even on ported (or disconnected) it drops in half.

Not sure the stall of the converter, it is extremely low though.

I can easily get the car to idle around 500 rpm in gear while maintaining close to 900-1000 rpm in park (which I am much more comfortable with), but it takes a lot of throttle to overcome the torque converter beyond around 500 rpm. So when I set it for 650 in drive and drop it back in to park it revs way up.

I guess I will leave it around 500/900 since the car runs fine like that. I was just pleased with the extra responsiveness I felt with the in drive idle set around 650 and was looking for a way to keep it there without having to slam it into gear each time.

Thanks,
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Last edited by AZ455; March 28th, 2012 at 09:30 AM.
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Old March 28th, 2012, 10:49 AM   #5 (permalink)
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Well... I am going to set the idle mixture in drive like the manual implies. Always done it in park before.

Will post results.
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Old March 28th, 2012, 03:13 PM   #6 (permalink)
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Thumbs up Update

If anybody is interested, here is how everything ended up.

  • Idle mixture: ~4 turns from all the way in
  • Idle: 600 RPM - Drive / 1000 RPM - Park
  • Timing: 12 @ 1100 RPM
  • Vacuum Advance switched to ported
  • ~17" vacuum @ idle

I would prefer to run the vacuum advance off of manifold vac for the extra cooling at idle, but it is what was causing the HUGE drive/park idle difference. It is alright though, maybe creep up to 210 idling, but will come down quickly when driving.

Using this with 87 octane gas.
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Old March 28th, 2012, 03:13 PM
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