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Discussion Starter #1
Hey guys,

I've got a 99 Rav4. Automatic, 4 door, 4WD.
It's got about 125k miles on it.

Been stuck dealing with error code P0120 [Throttle Position Sensor or Circuit Fault] and I don't know what to do.

Here's the backstory:
Engine's been acting weird. While idling at a stoplight, sometimes the RPMS jump to 1100 or 1200 for 5 to 10 seconds, then dip back down to 700 or 800. This'll happen if the check engine light is on or off.
The main issue is when the check engine light is on, sometimes the RPMS fall and I lose power with the car. Usually when I'm driving on the freeway.
I tried flooring the accelerator when this happened one time, and the RPMS didn't jump back up. After about 5 or so seconds of dropping, they eventually jump back up to around 3k, which is a normal RPM for me on the freeway. But the car may continue to rise and fall in RPMs and it feels like its chugging along.

The code I got from my OBDII scanner is P0120 [Throttle Position Sensor or Circuit Fault].
I checked the voltage to the TPS's harness connector and got 4.9 to 5.1 volts, measured at 200V. Which is normal.
Then I checked the harness connector to see if I was getting suficient ground. I got about 057 Ohms measured at 2000 Ohms. Also normal.
Then I checked the resistance on the TPS itself and got .47 Ohms measured at 200 Ohms. And when I opened the throttle, the resistance increased as well without any jumps. Normal.

So my TPS seems to be working. So I went to the store and bought some Throttle Body Cleaner and sprayed that and got a bunch of gunk out.

The light comes on, maybe for a day or three, and then after the car sits overnight, will usually turn off.
It comes on more when it rains. Also, the engine has died twice while it was raining and I was making a left turn. The radio and lights continued to work, but I had no power to the engine. Turning the car off then back on caused it to work.

I don't really know what to do next. I don't want to take it in yet because I feel they'll swap out the TPS and charge me an arm and leg, and the problem will continue.
The next thing I'm thinking of doing is removing the Throttle Body and cleaning the hell out of it.

Is there anything that I'm missing or overlooking?
 

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Only other things that I can think of would be loose/corroded battery terminals, grounds, or fuses... possibly a faulty contact in ignition switch. Seems like tps is ok according to your findings.
 

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1999 Toyota RAV4 with 3MZ-FE 6 cylinder engine, camo wrap, OME lift, heavily modded
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Check MAF Airflow sensor, this is likely to be part of the problem and/or poor connection or ground. ECU could be an issue not likely, usually it's the throttle position and/or MAF sensor. Ground the engine with a jumper cable directly from the negative side of the battery. Check the battery ground point and battery terminals, clean and use dielectric grease to prevent future issues. A bad alternator can cause issues as well.

See Throttle Position Sensor Out of Adjustment Due to Wear/Carbon Build-up : Toyota RAV4 Exhaust and Emissions

The MAF Airflow Sensor

Hopefully some of this helps. Let us know what you find.
 

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1999 Toyota RAV4 with 3MZ-FE 6 cylinder engine, camo wrap, OME lift, heavily modded
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The code I got from my OBDII scanner is P0120 [Throttle Position Sensor or Circuit Fault].
I checked the voltage to the TPS's harness connector and got 4.9 to 5.1 volts, measured at 200V. Which is normal.
Then I checked the harness connector to see if I was getting suficient ground. I got about 057 Ohms measured at 2000 Ohms. Also normal.
Then I checked the resistance on the TPS itself and got .47 Ohms measured at 200 Ohms. And when I opened the throttle, the resistance increased as well without any jumps. Normal.

So my TPS seems to be working. So I went to the store and bought some Throttle Body Cleaner and sprayed that and got a bunch of gunk out.
On the TPS connector the 3 signals are:
Pin 1 = E2
Pin 2 = VC
Pin 3 = VTA
It is useful to know the names, if you have to chase the signals to the ECM.

Pin 1 to pin 2 or VC-E2, should be 4.5 - 5.5 volts with the ignition switch on.
Pin 2 to pin 3 or VTA-E2, should read:
0.3 - 0.8 volts, ignition on and throttle closed,
3.2 - 4.9 volts, ignition on and throttle open full.

To check the wires and the TPS from the ECM connector:
Measure with the connector unplugged from the ECM.
VTA-E2, 3K-10K ohms with the throttle fully open, and 200-800 ohms fully closed.

57 ohms to ground seems too high, but I haven't measured mine.
.47 ohms on the TPS would be a dead short electrically. Which pins did you measure?

If the P0120 is the only code, I would take another look at this circuit.

Good hunting.
 

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Discussion Starter #6
From top to bottom my wiring goes Blue/Red, Orange, Yellow. Based on my readings I was working under the assumption that:

Blue/Red = Signal
Orange = Ground
Yellow = Supply

I ended up remeasuring everything and back probed the wires to get better readings.

Supply to Ground I got 4.9v.
Between ground and supply I got .6v throttle closed and 3.9v throttle wide open.
I'm super sure of these numbers.

Not so sure about these numbers, because it's hard to read my notes...
but, I got .47K Ohms between signal and ground.
2.9k Ohms between signal and supply.

At any rate the idiot light has turned back off. I don't know if this fixed it, but I ended up using forceps to squeeze the terminal connectors together inside the TPS connector. The ground connector seemed pretty open and I figured maybe it was coming off the terminal inside the TPS.

Fingers crossed for now, I'll let you all know if it comes back on. I'm sure it will. I also bought Mass Airflow cleaner, so if it does turn back on I'll use that.

Thank you for all the help so far guys.
 

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1999 Toyota RAV4 with 3MZ-FE 6 cylinder engine, camo wrap, OME lift, heavily modded
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Hopefully you've got it, good work with the diagnostics. I'm going to save your notes just in case I have this issue some time in the future.
 

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Discussion Starter #8 (Edited)
Well I'm back.

Light came back on. I was going about 45 or 50mph, weather outside was in the high 30s low 40s, brisk, no rain, and boom. Light turned on.
Drove it home and checked the codes. Now I've got:

P0110 - Intake air temperature sensor or circuit fault
P0120 - TPS or circuit fault
P1133 - Air/fuel ratio sensor or circuit fault

I know nothing about the other two codes. I'll start digging into them tomorrow morning.
All three codes have a circuit fault possibility, so I'm assuming it's that.
Maybe it's the ECU?

What do you guys think?

Edit:
So I was looking around under the hood. I've got the battery, then the fuse box with 3 fuses. Then there are 3 white wires which connect to a slew of wires of every color. Looks like a previous owner had made some modifications.
There's a fatter blue wire with a red stripe. It looks like that wire houses a red wire and a green wire. Green wire doesn't go anywhere, I think that's a ground wire, but I'm not sure. Red wire goes off and is spliced in and cut in weird ways... looks like it goes to plug that sits on the back left bottom corner of the engine if you're facing it while standing in front of the car.
Checked my Chilton book and it looks like the only thing in that area is the Injector or OCV. Not sure if this is part of the problem. But it's the only wiring that I can see that looks modified.
 

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Before you condemn the ecu...find grounds and wiring harness related to all of the listed sensors and check for corrosion and damage. Check for chaffing and see if you can find an intermittent connection
 

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As part of an earlier post by another, check your engine ground -- there's a slight chance it's the cause. The original ground (UK: earth)wire (braided copper) should be off the back of the engine to the firewall, and was in a plastic sheath that retained moisture so they rotted. See my post from years ago about adding a second ground easily from the battery to the engine.
 

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Discussion Starter #11
Engine ground looks good.

Looks like the only connection issue leads to the camshaft position sensor. At least that's what I'm thinking it is.

There's a Blue wire with a red stripe. They house a red wire, green wire, and a copper covered wire.
Green wire has been cut and doesn't go anywhere. Red wire and copper wire (I'm assuming ground) connect to the Camshaft Position Sensor connector. Could this be the culprit?
 

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Discussion Starter #13
So I haven't posted enough to submit a link. But they're on Imgur. Just go to their homepage and after .com, put in: /a/Kkl5G

So the second photo shows the blue/red wire which houses wires 1,2,3. 1 is the green wire that doesn't go anywhere. 2 is the red wire. 3 doesn't have a color. I'm assuming it's a grounding wire, but could be wrong.

The smallest white wire in photo 3, that's the same white wire you see in photo 4.

The last photo shows the black and white wire that leads to the connector that plugs into the CPS.
The white wire is split into wire 1, the fat gray wire, which leads to the ECU under my radio in the cabin. Wire 2 (black with white stripe) connects to the green and unshielded wire above. Wire 3 (black wire) connects to a fatter blue wire that isn't connected to the blue-red wire above.
 

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2008 RAV4 Limited V6
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So I haven't posted enough to submit a link. But they're on Imgur. Just go to their homepage and after .com, put in: /a/Kkl5G
You can post your pictures now. All it takes is a 5 post minimum.
 
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