I’ve been reading through the forum, and there’s a few posts on TPS for the x300 so apologies if there’s a double up.

Long story short: My X305 is running rich, strong fuel smell at idle. Idle rpm is about 750 rpm when cold.

What I did: Using my Autel AP200, I checked for fault codes and found: P1512 - Closed throttle position switch low input.
Then I used the OBD2 scanner to check the throttle readings which were:
Idle:
$18: 0% (It might have been 0.4% when at idle and 0% with the engine off but the vehicle power on)
$51: 0%

Full Throttle (actually taken with the engine off but vehicle power on, throttle pedal fully depressed):
$18: 71.4%
$51: 61.6%

So, a few questions;
1) What do $18 & $51 mean and why are they different?
2) The x300 forum said that idle should be ~12-13%, does the fact mine reads 0% indicate that it needs adjusting?
3) Is it an issue that the max position reads 60-70%

My planned next steps (as well as fixing a few other little niggles):

1) Get a multimeter and check the TPS reference voltage.
2) Check the voltage through the range of throttle positions.
3) The AP200 does have a throttle position sensor calibration feature, I’m almost too scared to try it as I’m not sure what could go wrong.

Open to ideas, will keep you posted, but this is a slow burner.

 

$18 represents the Transmission Control Module
$51 represents the Engine Control Module

I hope I remembered the affiliation correctly! (EDIT: I did.) The modules share a lot of the same OBD data. I think the Autel scanner is a good one, possibly as good as it gets with the X300/305. But these cars are known for glitchy first-gen OBD.

I got a code for the idle switch a while ago too and started looking into it. On the TPS the Black/Green (ground) and Orange/Yellow wires go through the idle switch, which is inside the TPS. That should be easy to check with your meter as you rotate the throttle pedestal. The switch should be closed at idle. I did not find any faults with mine and the code did not come back. I did not have any running issues at all.

I read similarly for the throttle on my Foxwell scanner. 0%/75% or so. I don't know if it is an error in the data read but it could be. If you were to add 13 to both numbers that would be a more appropriate zone for throttle position. I checked for throttle cable slack and made slight adjustments but did not notice a difference.

The idle switch is "probably" involved with fueling at idle, so that could be a root cause. Not certain in my own mind yet.

I believe new TPS are available. It is a delicate operation to calibrate a new one.

 

Excellent, and looks like there’s a similar post on the x300 forum as well. Although I think the x300 sensor is a different part.

I’ll do some testing with a multimeter at the sensor and see how that goes. Will loop everyone in when I’ve had a chance to investigate.

Nathan.

 

I checked my car again tonight. Near the same results as you Nathan. Engine module, 0%/72%, Trans module, 0%/82%. Top reading was with the kickdown switch pressed. Strange that the TCM would read 10% higher.

Regarding fuel odor: Be sure to take a look at the two rubber fuel crossover hoses between the fuel rails. They deteriorate and should be replaced at this age. If not sooner!

 

Really interesting, two different OBD2 readers as well, with similar results which aren’t consistent with what the reading is supposed to be.

Thanks for the tip on the hoses, will definitely check them out. I’m really still learning about the x305, so really appreciate the help. I’m having an absolute ball learning about the car.

 

Make sure those idle air control valves are clean. Mine was idling at low RPM when cold until I cleaned them

 

Do we yet know what the solution to this issue is? The car only started throwing this code when I did a slight adjustment to the throttle linkage because it was very loose and sloppy.

 

No updates from me. Other than I cleared the code, and it’s not come back. The throttle readings are still 0%-70%, so will try and measure the voltage directly to see if it’s the sensor itself or the calibration. There’s a similar post on the x300 forum that I’m also monitoring.