Idle question
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Tuned
Joined: Jan 2013
Posts: 305
Likes: 7
From: Middleburg, FL
Idle question
Is it normal to have a 250 to 300 rpm swing in idle speed when in park or neutral as compared to in drive or reverse? Just installed a new IAC and idle speed in park is 1000 rpm and 700 when in gear. I would prefer the in gear idle to be 750 rpm due to when stopping in gear the rpm's will initially fall to about 600 for a second before leveling off at 700 and actually stalled on me today in a parking lot.
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Tuned
Joined: Jan 2013
Posts: 305
Likes: 7
From: Middleburg, FL
At that rpm, do you ever stall if you quickly stab and release the gas pedal like in a parking maneuver or something similar? So your idle speed remains constant, as in no difference in rpm's between park and in gear?
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Tuned
Joined: Jan 2013
Posts: 305
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From: Middleburg, FL
Thanks Conanski, I checked the TPS voltage prior to replacing the IAC and it was .95 closed and 4.56 wide open. I do have a new motorcraft TPS though so I'll go ahead and replace it since it is probably the original and truck has 150,000. When is it acceptable to adjust the idle screw?
Posting Guru
Joined: Oct 2013
Posts: 1,039
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From: NC
No it doesn't stall and the RPMs stay pretty much constant. I can't imagine idling at 1000 in park is correct. 1000 for me is when the choke is on first thing in the morning. I know it's not a choke, but whatever the cold idle is.
Logistics Pro
Joined: Mar 2005
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From: Mexico, Missouri
Thanks Conanski, I checked the TPS voltage prior to replacing the IAC and it was .95 closed and 4.56 wide open. I do have a new motorcraft TPS though so I'll go ahead and replace it since it is probably the original and truck has 150,000. When is it acceptable to adjust the idle screw?
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Tuned
Joined: Jan 2013
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From: Middleburg, FL
Wrong terminology. Is the idle strictly controlled by the IAC and ECU with no manual adjustment? If so, could this only be corrected with a tune/chip?
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Yes... but with feedback from the TPS and the factory idle speed is 680rpm or so depending if it's in neutral or in gear, AC on or off, etc. If you can confirm the TPS not only measures correctly at closed and WOT but also sweeps evenly with no glitches then it can be eliminated, then you are back to a sticking throttle cable or a small vacuum leak somewhere... could be from a leaking EGR valve or tube, leaking brake booster, cracked vacuum line, or a leaking intake gasket.
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Tuned
Joined: Jan 2013
Posts: 305
Likes: 7
From: Middleburg, FL
Yes... but with feedback from the TPS and the factory idle speed is 680rpm or so depending if it's in neutral or in gear, AC on or off, etc. If you can confirm the TPS not only measures correctly at closed and WOT but also sweeps evenly with no glitches then it can be eliminated, then you are back to a sticking throttle cable or a small vacuum leak somewhere... could be from a leaking EGR valve or tube, leaking brake booster, cracked vacuum line, or a leaking intake gasket.
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Tuned
Joined: Jan 2013
Posts: 305
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From: Middleburg, FL
Update: Installed new motorcraft tps and adjusted to .98 volts, checked vacuum and holds steady at 19.5. Still idles at 1100 rpm in park or neutral and still has random stumble at idle. Also checked for codes with a reader and there are none. EGR valve is 2 yrs. old, TPS, IAC and EVP are new. Truck runs great above idle with no miss. The high idle in P and N doesn't necessarily bother me, but the stumble at idle and occasional dying out does. I have not checked fuel pressure, but I don't think that's the issue. Is it possible I could still have a vacuum leak even though the gauge showed good?
Lead Driver
Joined: Jul 2007
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From: Rhode Island
Update: Installed new motorcraft tps and adjusted to .98 volts, checked vacuum and holds steady at 19.5. Still idles at 1100 rpm in park or neutral and still has random stumble at idle. Also checked for codes with a reader and there are none. EGR valve is 2 yrs. old, TPS, IAC and EVP are new. Truck runs great above idle with no miss. The high idle in P and N doesn't necessarily bother me, but the stumble at idle and occasional dying out does. I have not checked fuel pressure, but I don't think that's the issue. Is it possible I could still have a vacuum leak even though the gauge showed good?
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Tuned
Joined: Jan 2013
Posts: 305
Likes: 7
From: Middleburg, FL
There is enough slack in the holes to slightly twist the unit in either direction to change the voltage. One way I could get it down to .8xx and over 1.0 the other way. I've always heard it's best to get as close to 1.0 as possible without going over.
