DIYLex

I want to check my IAT sensor on my 99 RX300 to ensure that it is working correctly.

The IAT sensor is housed in the MAF but which are the correct pins to use in order to check the resistance? I have the values for a range of temperatures but not sure on which pins to ohm out.

Lexmex

Welcome to the Club.

Actually, there is a code, P0110 Intake Air Temperature Circuit Malfunction that will come on if you have an issue.

DIYLex

Thanks. The reason why I ask is because the factory service manual indicates to use different pins on the MAF for the RX300 vs the ES300. But when testing using the RX pins, my values are way off (which would indicate a problem) and yet when using ES pins I get the correct readings. I was told the FSM was incorrect and that indeed the RX uses the same pins as the ES. I just wanted to confirm this.

Lexmex

I am not sure I can help you on this one as I don't know what the pins used by the ES are. Their air intake system and even the 1MZFE motor is slightly different than that of the RX300.

DIYLex

Sorry if I'm confusing the situation. What I'm really looking for are the pins for the 99 RX300. I've been told that the pins in the FSM is incorrect for the RX and when I use those specified in the FSM, my readings are way off. I'll replace the MAF if the IAT is bad but I want to make sure that it's bad before I spend $100 or so.

Lexmex

I think I know which pins those are, they are on the far right side of the connector on the MAF. Unfortunately I don't have my camera up and running (it is getting fixed) in order to show you which ones.

DIYLex

If those are the ones I'm suppose to be using for my IAT sensor, then my readings are way off and most likely the sensor is malfunctioning. You identified the same ones that are in the FSM but I was told that the FSM was incorrect and should be using the two leftmost pins, the ones the FSM shows for the ES300. (BTW - I'm assuming the "far right side" means closest to the side mounting screw hole when looking directly at the connector pins, in the MAF sensor housing, while holding in the normal/mounting orientation). So no need for your camera (unless I'm still confused on the orientation).

Lexmex

It's strange. I was looking in my service manual, volume 1, where the P0110 code is mentioned and there is nothing in there about checking the MAF itself, only the ECM in the glove box and they show some diagrams in there about how to check it off of the ECM, but not the MAF. I remember my uncle and I checking the MAF back in December (I replaced it) and we checked the resistance using (if you are facing the connector on the MAF), the two furthest connectors to the right.

Lexmex

Okay, maybe I see the confusion. there is the resistance and then there is the operation for the MAF sensor. The one I was referring to was the resistance and that is the one I talked about in my previous post. But for the operation, it is the backside of the connector to the MAF (a.k.a piece that hooks up to the MAF) and it is the furthest wire to the left, and then you skip a wire and then that one. So if you going from the connector from the back, it would be wires 1 and 3, going from left to right.

DIYLex

I think that we're both on the same page but I decided to attach some pics.

The pic in this post are the pins for testing the MAF sensor, specifically voltage fluctuations when compressed air is sprayed into the MAF chanber.

The next post will contain the pins for the IAT sensor testing.

DIYLex

The pic in this post shows the pins for the IAT testing according to the FSM. Are these the same ones that you used or did you use the left most two pinns?

DIYLex

LEXMEX - I saw in some of your posts that you had used a Camry(?) ignition coil because the RX was not available where ever you were at but replaced it with the RX coil when you returned. Is there any particular reason you went back to the RX coil as Lexus has told me that the Camry/ES and RX are the same?

The reason I bring this up is because I bought the OEM DENSO coil (90080-19016) which according to Lexus is the replacement for the 90919-02234 but I can't get it to slide down the spark plug tube...it stops at the first ring on the coil tube. The same happens when I try fitting it into the other two cylinders so I know that it's not just something with my # 2 cylinder tube. It has the Lexus parts guy baffled why it won't fit and yet it has the proper part number that should fit the RX/ES/Camary. Any clue?

Lexmex

Yes, those are the pins. Sorry for the late response.

With regard to your question on the coils. They were slightly different. The coil in question was used for the previous generation V6 Camry. I was living in Mexico at the time and they had only opened their doors in early 2002, so luckily that Camry had something that could be modified. Take a look at this thread and it will show you something of the difference (though I had to sand it down on the sides), https://www.clublexus.com/forums/sho...d.php?t=292508

Keep in mind there are some minor differences between the 1MZFE engine in our RX and those in other Toyota/Lexus vehicles, though are 1MZFE is the most powerful of the bunch.

When I switched the coil to one for the RX, I noticed a slight difference on the acceleration, small but just noticeable enough, like a small kick.

Take a look on that thread. It's exactly the same one I shoved down my tube. It's actually one one of my front cylinders. Not sure if it is catching on the top of the spark plug as plug head would have to go inside the bottom of the coil.

DIYLex

Thanks for the reply. Looks like I may actually have a problem with my AIT sensor because if I use the right most two pins (as in the 2nd pic), my values are way way out of range. Strange, though, is that the car is running fine and I'm not getting a CEL. Any idea what the symptoms might be if it was bad?

As for the coil: interesting. Even though I bought the correct (replacement) part according to Lexus, I too had to sand down the "rings" in order to make it fit (I had seen in other postings that a couple of people had encountered this same problem for what should be a direct replacement part). However, shortly after doing that, my car started misfiring again and I found two hairline cracks on the plastic tube where it was arcing. I took the coil back to Autozone (where I bought it) and they replaced it free of charge...the second one they gave me was actually the original pn (90919-02234) and not the replacement, and it fit perfectly without any sanding. Now my RX is back to running great. Makes me wonder if A/Z is selling refurbished coils but not advertising them as such...but the price was right ($60+tax).

Lexmex

When you get something wrong with that MAF itself, the vehicle may feel a bit rougher, say when you step on the pedal it might feel like it takes a bit more force to step on it. I would run an OBD2 test at Autozone and see if you pull up a pending error. That is an error that won't be enough to trip a Check Engine Light, but still pull up a possible code. Would be interesting to see if there is anything in the computer.

That is odd about the coil. Not sure what Autozone really sold you.