How do you adjust up idle on ST185?

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How do you adjust up idle on ST185?

Postby EvilStig » Tue Aug 13, 2019 5:59 pm

Hi,

I have a problem with the idle being way too low, and it tends to drop off and stall if you let of the gas suddenly (partly due to lightened flywheel I think). But really it's just too low, around 800RPM, and it idles really rough. I'd like to bump it up to 1100 to smooth it out and prevent stalling. I can't seem to find good info on how to do this though. Some posts on the MR2 forums mention that you need to adjust the throttle stop and then remove the throttle body and tune the throttle position sensor to compensate, but I can't find more detail on the procedure than that. Does anyone have first hand experience to help with this, or know where I can find a guide to follow? thanks.
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Re: How do you adjust up idle on ST185?

Postby 93celicaconv » Tue Aug 13, 2019 7:41 pm

IMG_0646B.pdf
(236.51 KiB) Downloaded 10 times
The factory set idle speed on an ST185 USDM is 800 RPM. If that is the idle speed yours is running at, I would say your idle control is working well. If the engine is running rough, I would suggest you address the cause of the roughness - idle speed increases for the sake of reducing a problem having a different cause isn't usually wise.

If you feel you must increase your idle speed above factory setting, see attached pic.
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Re: How do you adjust up idle on ST185?

Postby EvilStig » Tue Aug 13, 2019 11:11 pm

93celicaconv wrote:
IMG_0646B.pdf
The factory set idle speed on an ST185 USDM is 800 RPM. If that is the idle speed yours is running at, I would say your idle control is working well. If the engine is running rough, I would suggest you address the cause of the roughness - idle speed increases for the sake of reducing a problem having a different cause isn't usually wise.

If you feel you must increase your idle speed above factory setting, see attached pic.


incidentally every time I've taken it to get smogged, they've told me the idle was too low and I should get it fixed. They've said it needs to be 1300.

If it is indeed 800, I marvel at the apparent fact nobody else seems to complain about this. I had assumed that it just had to do with the way this particular motor was balanced. It runs smooth as silk above 1000rpm, but at 800 the whole car shakes and everything in the cabin rattles because it's getting so old that it just can't handle the constant low frequency vibrations.
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Re: How do you adjust up idle on ST185?

Postby 93celicaconv » Wed Aug 14, 2019 1:35 am

My son has two ST185's, and both engines are silky smooth at 800 RPM. They sometimes dip to 600-700 RPM for several seconds, but they are very smooth.

Now that I think about it, if you went to a light-weight flywheel, this could be your cause. Could also be a cylinder on your engine has lower compression than the rest. Or a fuel injector is metering out too little fuel than the rest. Any of these could magnify a normal idle speed to be less smooth at 800 RPM than higher. Compression is easy to check - not so much the fuel injectors. But something to think about.

Get a timing light to make sure your timing is spot on, and that you are getting strong spark on all 4 ignition cables, and check your plugs to make sure they are clean and that they are sparking strong. Check your front/back (relative to the car) engine mounts to make sure they are functioning properly also.
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