Problem: High Starting Idle

[86SupraMKII]

Since I got my car it's always started with a high idle, even it's a nice warm day. It'll run at about 1100 or 1000 RPMs for about 2 or 3 minutes then it'll drop down to normal running speed. Is there something that regulates the speed a cold running temps? I just think on a nice warm day it should't be idling high. Any ideas? :?:

[SilverMk2]

Sounds normal as long as it drops to 650 rpms after a while. The idle speed control motor raises the engine speed when the coolant is cold, common on most EFI cars. This helps to get the converter lit off for emissions purposes.

[trdmkii]

yeah, my supra does start off high unless the car is already at temperature. But my car idles really low....like 400, without any excessive engine vibration. It kind of suprises me.

[86SupraMKII]

I just thought it sounded not normal...I've had a few cars in my day and didn't think this was quite right, but is there a part I could replace to check it out?

[zank]

i have the same thing on my car where it idle is up in the 1-1.2 for a couple of minutes. some one told me to check my thermostat because it might be stuck open. I still havent gone and checked it.

[sloopercat]

There is a device that bypasses the throttle plate, it is called the ISC (idle speed control) valve. That could be bad, dirty, sticky. There could also be vacum leaks. The throttle plate could be dirty, so it does not seat well. Accelerator linkage could have problems. Cold injector not shutting off right away....

Most likely culprit is the ISC is a little sticky. I don't see any instructions on servicing the ISC in the TSRM. I would imagine you could remove it and clean it up.

[86SupraMKII]

Thanks for the input guys. I know it's not the thermostat, there is a new one installed, but I'll look in my Supra repair manual for the ISC controller.

[86SupraMKII]

Well guys, I just got my Supra out of storage....the high idle is higher than I thought....it's around 1500 to 1800 RPMs.....I knew it wasn't normal....so I should check the idle control? Where's that located?

If anyone can help let me know...thanks

[Jay]

You can do a rough adjustment to your idle with the screw on your throttel body, just above where the throttle buttefly is (right where the intake pipe meets it.) however, if you adjust this while the engine is cold, be prepared to do it agian as soon as it warms up, you might find the idle dropping too low. In the winter mine usually starts cold and idles at about 1100 - 1200 for maybe 30 seconds, drops to 900 for a minute, then idles normal at 650. I thought it was just normally that way.

[86SupraMKII]

The idle is just about perfect when it's warm....the idle is too high when it's cold...all the time...even in the summer.

There's got to be something else to adjust than the throttle cable.

[FWDsux]

Both my 83 and 84 when first started for the first time in a while(engine cold) idle high....The colder outside, the higher. At about 30 degrees, it starts at almost 2K then slowly works down to 700 (normal). Even when it's warm outside they still idle almost 2K, but come down quicker to 600-700.

Nick

[Supra Bob]

I watched my car today as I cold started it twice. Once was at 5am, when it was about 35 to 40 degrees out... here's how it played out..

0 to 10 seconds- 2000 rpms
10 to 45 seconds- slowly, gradually dropped to 1400
45 seconds to 2 minutes- dropped to 900 rpms
2 minutes to 3 minutes 10 seconds-800 a

and then it went to a normal idle...


It did the same thing at 7:15 pm... around the same outside temperature. This has been the normal routine for it since I got it...

[trdmkii]

no offense to whoever said rough adjust by the screw on the throttle body....that depends on what year. From 84 on the idle is computer controlled and cannot be adjusted manually. Sometimes the idle control and other systems can become tempermental when it get that old. That idle isn't that high really. I mean the purpose of the cold start switch is to have the idle higher until the coolant gets closer and closer to normal temperature. With the higher idle the coolant heats up faster.

[Jay]

My bad on the idle screw then - all 5 of my Supras have been 83 or older.

[Dave A.]

8) The fast idle speed is controlled by the relationship between the engine temp. sensor signal present at the THW terminal on the ECU and the ISC valve. As the engine warms up, the resistance of the engine temp. sensor changes causing the DC voltage at the THW terminal to gradually decrease, which in turn causes the ECU to gradually close down the ISC valve and lower the idle speed. The colder the engine temp. sensor, the faster the initial idle speed. Even on a hot day the engine will cool down some after it's been shut down for awhile and cause the THW signal to change. This is why the engine will start with a higher than normal idle speed after you return to your car after shopping for groceries. :-) If you shut the engine off and then fire it right back up, the idle speed will be the same as before since the engine is still at operating temp.. Generally, the colder it is outside in the AM during the first start of the day, the faster the idle speed will be after start. This helps compensate for the change in oil thickness in cold weather. The curb idle speed should always be adjusted with the engine at normal operating temp. and after the engine temp. sensor resistance has stabilized. The ECU also senses load so switching on the A/C will up the idle speed a little to compensate for the load placed on the engine by the A/C compressor.

[Malloy]

Welcome Dave A. 8) Im glad to see another pillar of mk2 info has joined the pesky web forums.

[Dave A.]

The cold start system basically just emulates the choke valve and fast idle cam on a carburetor. Hmmm, I thought all year MKII's had a idle speed adjustment screw on the TB. There should be an adjustment screw covered by a rubber plug on the TB.

[Dave A.]

:D Thanks, Mike! !

[Dave A.]

Hey Mike, BTW, what's that plunger device that you're pushing down? Is that a bell ringer or some sort of new hi-tech pneumatic shifter? LOL!!! Just kidding!!

[Malloy]

LOL, its a billet shift knob :D

[MkIISuperSupra]

Welcome Dave A. 8) Im glad to see another pillar of mk2 info has joined the pesky web forums.

I agree 100% !!! :lol:

Glad you found your way to the forum. Your imput is always welcomed.

Leslie

[Borlax]

I normaly had about 1000-1200 rpm on a cold start, but when i removed the A/C completely, the idle went up to 1600-1800 rpm at cold start, it´s a bit annoying because i have a open muffler so my neigbours think im crazy, when i start in the morning and wake up everybody. :cry: