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Super Fast Idle: Code P1120 Throttle Position Sensor???

SyberTiger

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2002 Limited 4x4 4.6L
The last couple of weeks I've noticed my engine idle running a bit fast even after the vehicle is running at optimal temperature. It started out that the idle would be 900 - 1200 RPM (vehicle in neutral) on various days. Then on another day it would be back at it's typical 700 - 750 RPM. It didn't throw an engine code for a couple of weeks but then did the other day under no particular circumstances to note other than what I described above. The code is P1120 - Throttle Position Sensor (F48F-9B989? or F4SF-9B989?). Today the RPM really climbed such that at idle with the vehicle warm but sitting in neutral it jumped up to 2000 RPM and pretty much stayed there the rest of the day no matter how many times I would restart the engine during different times of the day.

The high idle RPM reminds me of when my IAC went out. When that happened the RPM was 2200 -2400 RPM but under that circumstance it never threw an engine code.

Has anyone here had the P1120 code and did your engine behave like I described? Is there an easy way to check the throttle position sensor to figure out if that's the culprit? Is the part so cheap ($20) that I should just replace it and hope the problem goes away?
 
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SyberTiger

Well-Known Member
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2002 Limited 4x4 4.6L
I guess no one has had this issue. Oh well...never mind. I went ahead and cleaned the MAF and IAC then did my version of cleaning the throttle body. It seems like I just did all this 6 - 10 months ago so I'm surprised I would have to do the cleaning again. In addition, I did the crazy reset/recalibrate the PCM thing that some swear by.

Anyhow, my idle is now back to normal (625 - 700 RPM) and the engine hasn't thrown a P1120 Throttle Position Sensor code today. I don't know if this means I'm good to go or the problem will just randomly show up again.
 
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rrgone

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'02 XLT
You have certainly had your share of idle problems. Your thread on replacing the rubber hose elbow is a classic and should be a sticky in here. How many miles are on your Explorer now?
 
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SyberTiger

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2002 Limited 4x4 4.6L
You have certainly had your share of idle problems. Your thread on replacing the rubber hose elbow is a classic and should be a sticky in here. How many miles are on your Explorer now?

I know, right? I must have had more idling problems over the years than anyone. You'd think I'd be an expert at it now. Yup, that rubber elbow problem I think was the beginning of idle problems. I see that that original post is over 6 years old and I had 91K miles at the time. Now I have 136K miles on the ol' Explorer. I'm driving only 7500 miles per year on average and I know that 2000 of those miles every year are from making two round trips to Atlanta and back for Thanksgiving and Xmas meaning I'm only driving 5500 per year around town. I'm starting to wonder it that's part of the problem....5500 miles of in town stop and go driving allowing crud to buildup in the intake, etc.

Two years ago was the beginning of my IAC issues. I think I'm on my fourth IAC. The BWD made IAC from Autozone was crap so I returned it. Then my Motocraft replacement died less than a year after replacement so Amazon sent me another one but that one was bad so I got yet another replacement. Whenever I had an IAC issue it never threw a code so when the P1120 code showed up recently I was at a loss to understand if the TPS was really bad. I guess time will tell but for now after doing the stuff I listed above my idle is perfect. Is it me or does it seem like having to clean the MAF, IAC, throttle body every 6 - 10 months seem excessive? Geez, I've been running mostly Shell's nitrogen enriched gasoline through the Explorer the last couple of years.
 
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SyberTiger

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2002 Limited 4x4 4.6L
This is an old thread but I never was able to close out this thread with a solution so I'm back to close it out...I think.

About six weeks ago I finally got around to changing out my leaking intake manifold. What was leaking? Well, for sure it was leaking coolant as evidenced by the observation of a little bit of coolant on top of the heads. This was a problem that I had known about and did nothing about for a long time because I only drove very short trips around town and avoided long trips away from town.

The one thing I never really gave a lot of thought to was if it was leaking (sucking) air into the injector ports where the gasket between the intake manifold and the heads could have also lost their seal. Now that I have the intake manifold replaced I'm pleased with how steady the idle is whereas it was a bit jumpy between 700 to 800 on a good day before the replacement. Now that I've had some time to enjoy a nice steady idle I got to thinking about "fuel trim". I'm now coming to the conclusion that my occasional fast idle was a result of the PCM performing fuel trim based on O2 sensor readings showing increases in air even though at idle I wasn't touching the throttle. In other words, I think my intake manifold was sucking in additional air around a leaking area and the computer was seeing it as though I was opening up the throttle and therefore the computer would dump in more fuel to get the system in balance and of course this would increase my idle RPM.

No one really had an answer to my original question about this phenomenon but I'm thinking my theory has merit. So, unless you see me bring up this old thread again to complain about fast idel then let's assume the problem was a leaking intake manifold because I'm sure, even though it's only been six weeks, I would have seen something odd about my idle RPM by now.

If anyone reading this thread is trying to address an erratic or high idle issue then also consider the problem could be a leaking intake manifold and not simply a vacuum line somewhere.
 
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