I need a little help with sensors

Allow me to fill in the back-story first, my car will barely run when I have the air conditioner on. I was told that I needed a idle speed sensor for my Miata so that the idle speed would remain constant, even with the extra load that the air conditioner provides. I contacted a few used Mazda part yards through EBay and ordered that I was told was the correct part. I tried to have the person that was working on my car install the new sensor and he was unable to do so since he said it was the wrong part. I took the sensor to a Mazda dealership yesterday and they said that the sensor I had bought was a throttle position sensor. My first question would be, is a idle speed sensor and a throttle position sensor the same thing? My second question would be, would replacing the throttle position sensor correct the huge drop in RPM when I turn on the AC. My RPM goes from around 1500 (I had to bump up the RPM to keep the car running) to around 200 when I turn on the AC. I would really appreciate the help. :salut:

What year is your car?

Found this easy way to check for a bad ISC Valve on Miata.net!

Quote:

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Bill Strohm

posted 26 June, 2004 12:19
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Here's a picture of the throttle body with the ISC valve mounted at the bottom. To test your ISC valve after doing a standard idle adjustment (per this Miata Garage article by Phil Logan), idle your engine at 850 rpm (if you can) and disconnect the ISC Valve electrical connector. If it is working, you will hear a "click" and the idle speed will rise to about 1200 rpm. If no click, then with the engine off, measure the electrical resistance between the two terminals of the ISC valve connector. It should be 11-13 ohms. If high, you will need to replace the ISC valve because its solenoid coil has gone open.

---- Bill

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http://www.inoneear.com/miata/tps.jpg
Ignore the arrows the are pointing to TPS not the ISC! :wink:

As far as I know, the TPS will help the ISC. Because the ISC positions depends on the throttle position. The problem is either one being bad could cause the idle problem. If your mechanic has already said it is the ISC, I would bet on that. He probably did what POS posted, to figure it out.

BTW I just looked up the ISC on Mazdaspeed. Ouch $343.90

Edit: If you dont mind, fill out the info on your profile. I guessed that you had a 91, but it might be different for a different year. It would help to know the year.

Quote:

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Originally Posted by Majik

If your mechanic has already said it is the ISC, I would bet on that. He probably did what POS posted, to figure it out.

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Depends on who his mechanic is, I'd still check it myself just to be sure that's the issue! Call it peace-of-mind! 8-)

Quote:

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Originally Posted by Majik

As far as I know, the TPS will help the ISC. Because the ISC positions depends on the throttle position. The problem is either one being bad could cause the idle problem. If your mechanic has already said it is the ISC, I would bet on that. He probably did what POS posted, to figure it out.

BTW I just looked up the ISC on Mazdaspeed. Ouch $343.90

Edit: If you dont mind, fill out the info on your profile. I guessed that you had a 91, but it might be different for a different year. It would help to know the year.

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Yeah, the year would be helpful... I have a spare 1.6L engine here that I'm putting a new crank in... but it has all the sensors & stuff still attached and I may be tempted to part with that sensor. ;)

Sorry about that, I tried to change my email address to the one here at work so that I could see if anyone responded to my post and the conformation email never came so I was unable to respond. I changed it back now so here I go. The car is a '93. I'm not sure what the mechanic checked to determine which sensor was needed. He did mention that the sensor would be around $300 new, thus the reason I tried to locate a used one. Is the ISC and an idle speed sensor the same thing (what does ISC stand for)? I printed the picture out that was posted and took a look to compare what I have to the picture. Is the ISC the sensor opposite to the TPS? I noticed what looked like another sensor located right under the TPS on my car and thought that this might be the ISC.

channelmaniac, if you are willing to part with this sensor that would be great.

ISC = Idle Speed Control

Ignore the arrows the are pointing to TPS not the ISC! The ISC is the lower unit on the picture, with the solinoid with the black can.
http://www.inoneear.com/miata/tps.jpg

I'd definaly try the test Bill Strohm mentioned, pretty easy way to see if it's truely the issue at hand!

Chaz were you able to figure out anything??

I havn't had a chance to test my ISC yet. Each time I attempt to unplug the ISC, the engine is too hot to reach the sensor. It seems that the ISC is located underneith the TPS on the '93. I need to wake up early some weekend morning and do a little research. I work 7 days a week and the only time I have to check the sensor is after work. I did have a chance to unplugg the TPS and I saw the RPM jump, does this mean that the TPS is good? I need to PM channelmaniac to see how much the sensor would cost.