'94 1.6 Idle - Toyota Nation Forum : Toyota Car and Truck Forums

bereta1 · 12-22-2010, 04:26 PM

Does the 1994 1.6 engine have a fast idle that's part of the warm up in cold weather. Mine seems to have a fast idle until it warms up.

Merry Christmas to all. TKU

Callum3 · 12-22-2010, 04:49 PM

yes that is normal (as long as its within reason...3000rpm idle isn't normal lol, but if its below 2000rpm that is good)

speedy25 · 12-22-2010, 07:35 PM

ALL fuel injected cars have the same thing.

-SP

bereta1 · 12-22-2010, 08:21 PM

What causes it to idle up? TKU

topnotch · 12-22-2010, 08:42 PM

sometimes caused by vacum leaks

ganda1f · 12-23-2010, 03:43 AM

Quote:

Originally Posted by bereta1

What causes it to idle up? TKU

Normally, when nothing is broken, the ECU reads the coolant temp and notices that the engine is cold. Then it will open the Idle Air Control valve (IAC) which is located on the throttle body. It allows air to flow through a by-pass channel around the throttle plate. The IAC valve is controlled by an electro-magnet. Once the engine warms up, the ECU will close this valve a bit, putting idle rpm at around 800.

bereta1 · 12-23-2010, 06:05 AM

Quote:

Originally Posted by ganda1f

Normally, when nothing is broken, the ECU reads the coolant temp and notices that the engine is cold. Then it will open the Idle Air Control valve (IAC) which is located on the throttle body. It allows air to flow through a by-pass channel around the throttle plate. The IAC valve is controlled by an electro-magnet. Once the engine warms up, the ECU will close this valve a bit, putting idle rpm at around 800.

Thanks for the info. I'll have it checked out.

ganda1f · 12-23-2010, 06:22 AM

A fairly common problem is that the IAC valve becomes sticky due to the oily deposits coming from Positive Crankcase Ventilation (PCV). Usually the valve gets stuck with little opening, causing low/rough idle on cold starts with a tendency to stalling. But if it was to get stuck in the open position one would get high idle instead.

Another cause could be a defective coolant temp sensor. If it feeds wrong information to the ECU, e.g. lower temperature than it actually is, the ECU will turn up the idle to have the engine warmed up.

Here is some info on how to check the temp sensors, both coolant and Intake Air Temp.
26mpg, good or bad?

bereta1 · 12-23-2010, 07:08 AM

Quote:

Originally Posted by ganda1f

A fairly common problem is that the IAC valve becomes sticky due to the oily deposits coming from Positive Crankcase Ventilation (PCV). Usually the valve gets stuck with little opening, causing low/rough idle on cold starts with a tendency to stalling. But if it was to get stuck in the open position one would get high idle instead.

Another cause could be a defective coolant temp sensor. If it feeds wrong information to the ECU, e.g. lower temperature than it actually is, the ECU will turn up the idle to have the engine warmed up.

Here is some info on how to check the temp sensors, both coolant and Intake Air Temp.
26mpg, good or bad?

Is the IAC on the throttle body, or, the firewall? I have a 94 Corolla. Thanks

Also, when I called about the part, they said there were 3 different ones, one for the fan, EFI, and, idle up. I assume the one I need is the idle up. The part # they gave was was 8942235010. Is there any way for you to see if that is the right one?

ganda1f · 12-23-2010, 10:51 AM

IAC is at the bottom of the throttle body (TB). It is a grey-green-ish rectangular plastic block, about 1x2 inches that is attached with two bolts and has an electrical connector. It is facing the front of the car. There is also a black one on the back side of the TB facing the firewall, this is the throttle position sensor. No need to fiddle with that.

First of all, does your idle ever settle down after the engine warms up? If it does, the IAC is most likely all right.

You can check the IAC if you disconnect the wire, undo the bolts and remove the green block which controls the valve. It may be stuck a little bit. There is gasket between it and the TB. You will see an axle with a metal knob kind of thing. This axle closes and opens the idle air passage. It should rotate completely freely from end to end. Think it is around quarter to 3 quarters of a revolution (90-270 degrees). It should not stick in any position. If it does, you can start with cleaning it using a carburetor or MAF (Mass Air Flow) sensor cleaner. Available in spray cans.
Remove the hose between the air box and the TB. You should see a hole at the bottom of the TB before the throttle plate. Spray some cleaner into the hole and wiggle the IAC axle. See if it losens up. Put back the green valve controller, reconnect it and start the car with a little bit of throttle. The idle passage will be flooded with the cleaner and the air has to go through somewhere. With the car idling spray a few small portions of the cleaner into the hole, add throttle by hand as needed to prevent the car from stalling. Turn off the engine.
Your TB will likely be full of oily crap so it is a good idea to clean it with a toothbrush and the sensor cleaner best you can while you are in there anyway.

No idea about the part numbers, but I would suggest to test the sensor first, before spending money at random parts. The sensor referred to in the link in previous post would be the EFI one.

I had no idea about any idle up temp sensor. Haynes manual never mentions it. Where is it located?
I know only about one for EFI, one for radiator fan and one for intake air temp.

speedy25 · 12-23-2010, 04:03 PM

Quote:

Originally Posted by ganda1f

I had no idea about any idle up temp sensor. Haynes manual never mentions it. Where is it located?

I fairly certain that the ECU uses ALL temp sensors to make adjustments as needed. There isnt just ONE "idle up sensor."

-SP

bereta1 · 12-23-2010, 04:05 PM

The idle does settle down after it warms up. I'm going to purchase a Haynes manual. Where is the EFI sensor located? The one that I see is on the right side of the thermostat housing, and, has two wires going to it. Thanks for the help.

ganda1f · 12-23-2010, 11:05 PM

Quote:

Originally Posted by bereta1

The idle does settle down after it warms up.

In that case, what is the reason for your concern? What are the engine's rpm during your fast idle and after it settles down? The ECU can raise the idle only as much as a fully open IAC would do, which I think is below 2000rpm as Callum3 said.
If you are idling higher than that, something else is wrong. Check topnotch's suggestion about a vacuum leak on the intake between the engine and the TB.

In addition to the sensor on the thermostat, there is also a coolant temp sensor on the elbow coming from the water pump. One is for temp gauge and one for EFI. Speedy25, can you comment on which is which. I can't tell off the top of my head.

bereta1 · 12-24-2010, 07:54 AM

Quote:

Originally Posted by ganda1f

In that case, what is the reason for your concern? What are the engine's rpm during your fast idle and after it settles down? The ECU can raise the idle only as much as a fully open IAC would do, which I think is below 2000rpm as Callum3 said.
If you are idling higher than that, something else is wrong. Check topnotch's suggestion about a vacuum leak on the intake between the engine and the TB.

In addition to the sensor on the thermostat, there is also a coolant temp sensor on the elbow coming from the water pump. One is for temp gauge and one for EFI. Speedy25, can you comment on which is which. I can't tell off the top of my head.

R's are closer to 3000. I'm going to have it put on a computer to see what's going on. Already checked for vacuum leaks. Thanks guys, for all the help. Merry Christmas!