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  #1  
Old December 16th, 2009, 12:24
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heyhar heyhar is offline
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Throttle Position Sensor

Today my '96 4.0 AW4, 142k miles threw a code. When I got home, I hooked up my scanner and got P0121-Throttle Position Sensor, Switch A ckt Range/Performance. I went to the yard and grabbed a whole throttle body, from a '96 with 119k miles. I'm going to clean one of them, and hopefully will have enough good parts to work. The best price I could find online was close to $50, so hopefully the $34 I spent will do the trick.

What exactly goes bad in a TPS? I'm going to disassemble the 'bad' one to see what I can learn. I've never run into this particular problem, so here's one more chance to learn a little more about what makes these beasts run.
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Old December 16th, 2009, 12:27
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kastein kastein is offline
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Re: Throttle Position Sensor

It's a variable resistor, pretty much - all it does is divide its supply voltage and return a voltage to the ECU indicating what angle the throttle shaft is at. That's why the voltage ranges from a bit above 0 to a bit below 5 volts, which is the standard supply voltage for TTL-compatible logic chips.

What wears out - if it wears out without any mudding/swimming incidents, the wiper just wears through the resistive strip in the spots it spends most of its time on. If you go mudding/dunk the thing, it gets waterlogged like any other electronics.
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My yard looks like Sanford & Sons.
Please do not PM me about the AW4 info thread unless you have a truly unique question that is not covered by it or info to add. I do not respond to questions answered by the thread.
Definitely do not hunt down my phone number at 3AM, text me about it, and then threaten violence when I am not helpful. It will not get you what you want.
CTeunuch: Sometimes I really wonder if this sport makes you insane, or it just attracts the mentally unstable.
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Old December 16th, 2009, 12:44
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heyhar heyhar is offline
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Re: Throttle Position Sensor

I just pulled the old one apart, unfortunately breaking it. Nothing inside seems worn or dirty, so I'm going to re-assemble it, and put my meter on it and try to get some readings. Then I'm going to try to read the 'new' one, and see if it's different or better. I hope I can figure out what I'm looking for!
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Old December 16th, 2009, 13:57
JJacobs JJacobs is offline
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Re: Throttle Position Sensor

It's a lot like a fuel tank sender if you've ever had one of those apart. There's a series of metal strips and a wiper that runs across them.
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Old December 16th, 2009, 14:20
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Re: Throttle Position Sensor

Now that it's apart, I'm embarassed at just how dirty the IAC chamber is. I wonder if the TBS didn't get confused trying to control the engine. I was going down a hill on I-81, where the speed drops from 65 to 55, and I caught up to a slower truck. I tapped the brake to dis-engage the cruise, and noticed that the tach was still at 2k, when it should have floated down to about 1500. The car didn't slow much, then I noticed the CEL. It just seemed to run funny on the way home, then I put the scanner on it. Now I'm giving it a good scrubbin!
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Old December 16th, 2009, 14:27
joe_peters joe_peters is offline
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Re: Throttle Position Sensor

While you have that TPS apart, see any ways of "weather proofing" it--would be a good write up.
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Old December 16th, 2009, 15:31
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kastein kastein is offline
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Re: Throttle Position Sensor

You could probably pack it with dielectric grease, not sure if overdoing it would result in a lack of contact - how "springy" is the wiper?

If not that, maybe filling it with a thinner silicone oil or similar would help.
__________________
My yard looks like Sanford & Sons.
Please do not PM me about the AW4 info thread unless you have a truly unique question that is not covered by it or info to add. I do not respond to questions answered by the thread.
Definitely do not hunt down my phone number at 3AM, text me about it, and then threaten violence when I am not helpful. It will not get you what you want.
CTeunuch: Sometimes I really wonder if this sport makes you insane, or it just attracts the mentally unstable.
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Old December 16th, 2009, 15:55
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B.RAIDER B.RAIDER is offline
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Re: Throttle Position Sensor

Quote:
Originally Posted by joe_peters View Post
While you have that TPS apart, see any ways of "weather proofing" it--would be a good write up.
And a pictures of the "guts" for the lack of a better description.
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Old December 16th, 2009, 20:50
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heyhar heyhar is offline
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Re: Throttle Position Sensor

Quote:
Originally Posted by joe_peters View Post
While you have that TPS apart, see any ways of "weather proofing" it--would be a good write up.
Problem is, as far as I can tell, the only way to get it apart is to break it. The cover that the shaft enters is glued on, and it will not break off clean. I did get it apart, but the cover shattered.


As far as weather-proofing it, there appears to be no way to waterproof the area where the throttle plate shaft enters the TPS without hampering the operation. Pardon the broken cover, and blurriness.


Also, the area where the TPS sits seems to be constructed to let water drain, but also allow it to enter in the first place. This scabby looking sample is the donor, not the one I re-installed. Note the slot at the bottom of the mounting area. Possibly if this were filled-in or sealed, it would be more water resistant. Also note the Obama Orange paint. Someone blew a whole can of it on this engine.


I installed the now spotless TB, started the car- no code present, although I cleared it before I started dis-assembly- drove it a few miles, and so far, so good. It idles rock-steady now, and a little slower. I think maybe the dirty IAC may have been the culprit all along.

Sorry about the oversize pictures. I'm still working on posting pics.
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