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Discussion Starter #1
Someone in this old thread mentioned a RPM sensor may cause idle speed surging:

http://forums.tccoa.com/showthread.php?s=&threadid=18699

Can someone tell me where the RPM sensor is located on a '95 LX 4.6L?

I have a problem with RPM dropping in Park or Neutral. The A/C clutch cycles in and out and when it engages it drops the RPM so low the engine almost dies. No problems when it is in gear though, nice smooth idle. Anyone have an idea what the most likely cause is?
 

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if your AC comes on and the engine bogs it's the IAC valve.

it should let more air in when the AC comes on.

About $50 bux at autozone
 

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even cheaper, check the TPS Voltage.... Should be at .98 volts... If it isn't and is way off, you have a bad TPS. I'm asuming you've done the basic troubleshooting? Plugs, Cleaning MAF??....My friends 90 GT Stang was surging, hooked up the multimeter, bam....bad TPS.... Just a thought....
 

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jordansypek said:
even cheaper, check the TPS Voltage.... Should be at .98 volts... If it isn't and is way off, you have a bad TPS. I'm asuming you've done the basic troubleshooting? Plugs, Cleaning MAF??....My friends 90 GT Stang was surging, hooked up the multimeter, bam....bad TPS.... Just a thought....
if it chugs and the idle goes to low when the ac comes on then the IAC is not doing it's job

the IAC is his problem
 

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I hear ya man, but its better to be certain, before you spend $50, and for something like an IAC, they probably won't take your money back if you try to return in if he finds out this isn't his problem. An IAC from Ford Lists for $85, so maybe you can try Dan to get a better price. You can get one from Autozone, but a lot of people have been down the "you get what you pay for" road, including myself. I will only use Ford sensors etc. To each their own, good luck.

As far as the AC firing on and off for a second, my Explorer does that, but only when the AC is on (AC isn't currently working). Chad, does the AC surging happen when it's turned on, or off, or doesnt matter? I thought the compressor only did that when it was low.

Thanks...
 

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if it cycles super fast you are low on refridgerent

-now I just thought of something

If the compressor spins for a sec and bogs the engine and then the it cycles off - then it sounds like your compressor ate itself. There is a sensor in the compressor called an RPM sensor and it will make it cycle if it is not spinning up to speed i.e. semi-frozen.
 

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If your compressor starts and bogs the engine it can be overcharged which will eventually frag the compressor. These systems are designed to hold a measured amount of refrigerant not just dump it in till it quits taking it
 

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Discussion Starter #8
timb said:
If your compressor starts and bogs the engine it can be overcharged which will eventually frag the compressor. These systems are designed to hold a measured amount of refrigerant not just dump it in till it quits taking it
I don't think it is either over or under charged, but will have it checked. It started doing this shortly after I changed the spark plugs. I was thinking something got unplugged or came loose while I was working around it.
 

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i doubt your cars acting up b/c you nocked a sensor off from doing your plugs, your car does this with the AC on like the other guys?
 

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Discussion Starter #10
The surging occurs with AC on in Park or Neutral. It idles fine with AC on in Reverse, or Forward gears, or with AC off in any gear. I'm not sure if this was the same symptoms as the other guys were having.
 
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