Throttle Position Sensor & Engine Idle

[pos]

Hello,

I have been scouring the web for information regarding setting the engine idle (tick over) speed for my manual import 1kz-te Surf. There seems to be lots of incomplete posts or broken links relating to setting the idle speed and I am really looking for a definitive answer please if someone can help. Essentially, I have adjusted my engine idle speed down from ~1000RPM to ~750RPM by adjusting the grub screw that sits against the throttle cable pivot on the air intake elbow. This seems to have worked fine and my truck runs really well but I have come across several posts that suggest I should not have adjusted this grub screw and that the ECU sets the engine idle RPM based on readings from the throttle position sensor. Can anyone advise why I shouldn't adjust on the grub screw when everything seems to work so fine? How should I have adjusted my engine idle? TPS repair guides / pictures and explanations are completely lacking, or I can't find anything firm.

Best regards,
-Tom

[NiftyNev]

Why did you decide to lower the idle speed? If you adjust the throttle stop screw then your TPS settings are not right, which, even though you may not notice much difference, may have and adverse affect on the engine in other ways.

Nev.

[pos]

Why did you decide to lower the idle speed? If you adjust the throttle stop screw then your TPS settings are not right, which, even though you may not notice much difference, may have and adverse affect on the engine in other ways.

Nev.

Hi Nev,

I have a feeling someone has tampered with it in the past in order to combat the signs of ageing engine mounts and a harsh engine wobble at idle. I replaced my engine mounts this weekend and decided that I'd lower my idle from ~1000RPM, which is really too high an idle speed, to the ~750RPM that it should be. Do you know what the other effects may be on the engine? This is the information I'd like to know if I can. No where seems to have an explanation.

Would I be right in thinking that it's related to the opening / closing of the EGR valve and fuelling at any given throttle position? All I can conclude is that the ECU knows the speed of the engine via the engine speed sensor in the injection pump but the only way it can determine load is via my throttle position. Even still, if I wanted more go, I'd just be putting my foot down a tad further.

If the engine idle is controlled by the ECU, why should I have so much room for adjustment on my throttle plate stop grub screw?

I'm interested!
Many thanks,

-Tom

[NiftyNev]

What engine do you have and is it auto or manual? Lots of things can cause rough idle. Any modifications to the EGR or other vacuum related parts?

Just as an example my 2.4 manual idles at around 825RPM. Autos should be around 900RPM IIRC.

Nev.

[RebelV8]

My 2.4 auto 2nd gen currently idles at 500rpm, I've been thinking that it's to low and was going to increase it to 750rpm, does it need increasing and if so should it be 750 or 900, I've never had an auto anything with an idle higher that 750.
I also use the grub screw on the throttle cable to change the idle speed, my EGR has been removed.

[pos]

What engine do you have and is it auto or manual? Lots of things can cause rough idle. Any modifications to the EGR or other vacuum related parts?

Just as an example my 2.4 manual idles at around 825RPM. Autos should be around 900RPM IIRC.

Nev.

Hi Nev. It's all in my original post. She's a Japanese import 3.0 1KZ-TE with manual transmission. The idle is not erratic, it's perfectly smooth but the engine was shaking on its worn mounts which I have now replaced.

Basically what I would like to know is whether or not the idle is ECU controlled once the TPS is resting in IDL position and what are the negative effects of adjusting my idle on the stop screw rather than by fine tuning the TPS location.

Thanks,
-Tom

[pos]

There seems to be no answer to this question anywhere on the internet despite the claims