Rough Idle with AC on
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Laughing Gas
Joined: Dec 2003
Posts: 751
Likes: 30
From: North Carolina
Rough Idle with AC on
2010 F150 4.6L 2V, 50k miles. Have recently developed an issue with an extremely rough idle with the AC on and trans in Drive. If in park, the idle is high enough that it is much less noticeable. I have cleaned my throttle body, and MAF sensor ? After this , I disconnected battery for about 30mins and let the computer reset. After a long drive today, it is still happening. This engine has the servo controlled throttle body, and therefore no IAC valve that I can identify. I would assume that the idle increase necessary for the AC to be on would come from the servo controlled throttle body itself with no need for an external IAC. The idle in Drive with the AC on will drop to 500 RPM or less and it is very rough. Is there a procedure for a recalibration of the servo throttle body that I could try ? Just looking for ideas at this point and thanks in advance for your replies.
Elder User
Joined: Jan 2010
Posts: 790
Likes: 3
From: Ontario, OH
i believe i read somewhere that if you turn the key to run, wait for all the warning lights to go out, then slowly push your gas pedal all the way to the floor and slowly let it return to normal, and then turn the ignition to off , that is supposed to recalibrate your throttle. Not sure if it works or not though.
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Laughing Gas
Joined: Dec 2003
Posts: 751
Likes: 30
From: North Carolina
Okay, looking to resurrect a dead horse . This issue has continued with no answer to be found. Then , last week I changed the plugs, and found this. This is a pic of one of the NGK platinums I took out. They were all virtually identical, so no need to post em all. This plug has about 50k on it. I noticed some slight gap growth (about .005") but nothing terrible. My point is this, it appears I am running very lean. This plug had virtually no deposits, no color...nothing. The truck is stock except for an aftermarket muffler, same diameter pipe, single outlet...basically just got it for the sound, it's a Magnaflow with an 18" long body, very mellow sound and may or may not flow better than stock. When I disconnect battery and let the computer reset, it seems to run much smoother with more power, I assume because it's operating off of a preset fuel and timing map until it "learns" more. Have had no codes or other issues. I used an entire can of throttle body cleaner trying to find a vacuum leak...but struck out. What are the thoughts on the plugs and the lean issue ? Why could I be so lean ? Why no codes ? [IMG]
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Posting Guru
Joined: Jun 2002
Posts: 2,091
Likes: 3
From: Suffolk, VA USA
A couple of thoughts. Run the leak test again, but use propane instead of TB cleaner. It can be a little more noticeable. Also, a bad O2 sensor or ECT sensor can be running out of range but not throw a code. Either of those will affect fuel mapping.
Thread Starter
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Laughing Gas
Joined: Dec 2003
Posts: 751
Likes: 30
From: North Carolina
Propane is a good idea, the only thing else I had was ether.... and I did not feel like blowing up that day 
How could I narrow down the which O2 without throwing parts at it ? Thanks for the input !
How could I narrow down the which O2 without throwing parts at it ? Thanks for the input !
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Posting Guru
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From: Suffolk, VA USA
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Cargo Master
Joined: Nov 2011
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From: Northern California
Besides giving a good visual test, here's a video that shows a good bench test.
How To Test An Oxygen Sensor - Old Vs. New - YouTube
How To Test An Oxygen Sensor - Old Vs. New - YouTube
Thread Starter
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Laughing Gas
Joined: Dec 2003
Posts: 751
Likes: 30
From: North Carolina
Okay, was able to get one off on passenger side, in the cat, 4 wire type. Tested it , and only got up to .7 volts. Could not get to others before it started to rain.. :/ The two upstream sensors are wideband type with what looks like maybe 6 wires. I will search for info on those two and how to test. I doubt I am lucky enough to get the bad one , out of 4, the first time out. Will keep all posted and any additional input is greatly appreciated.
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Laughing Gas
Joined: Dec 2003
Posts: 751
Likes: 30
From: North Carolina
Well...have not found any info on testing the wideband sensors, at least not that I can pull off. Will test the ECT tomorrow, as I suspect it could be a problem, considering both banks of plugs look the same. I don't think that one O2 sensor on one side would cause that.... but who knows.
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Laughing Gas
Joined: Dec 2003
Posts: 751
Likes: 30
From: North Carolina
Tested the ECT today, seems to work normally, high resistance cold (51k) and low when hot (2.8k) . Did a little experiment after warm up. Turned on AC, idle is rough when compressor cycles...unplugged the MAF sensor and the RPM rose slightly...maybe 150 RPM or so, and the roughness is gone. Now for your insight, is this caused by the computer resorting to a preset map or possibly because the MAF has an issue ? I also still wonder about the TPS that I assume is incorporated into the servo throttle body...any and all inputs appreciated.
Thread Starter
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Laughing Gas
Joined: Dec 2003
Posts: 751
Likes: 30
From: North Carolina
Well , replaced the MAF today and reset the computer.... no obvious change yet. I guess the search goes on. Anybody replaced their servo throttle body with a bigger one and want to sell theirs ... ?