Fixing High Fast Idle on 1MZ-FE V6

[artbuc]

I have a 99 Avalon but I wanted to post here because I know many Camry owners have the same engine and same problem. Many of these engines have a very high initial fast idle. Mine had increased slowly to 2100 over the last several years. On various automotive forums, 1MZ-FE owners have asked about this high idle and have been told it is normal. Many have gone to dealers who have told them it is normal. It may be normal but it is a royal PITA putting the car into reverse to back out of the garage when you car is humming at 2100 rpm.

I bought a 0 - 5k ohm potentiometer at Radio Shack for $3. I wired it in parallel with the ECT sensor. I calculated the required setting would be 1.6k ohm to give me a net resistance of 1.0k ohm which would "fool" the computer into thinking my car engine was 104 degrees F. This gave me an intital fast idle of about 1250 rpm. I tweaked it to bump up the initial fast idle to 1500. I may do some additional tweaking but I like the 1250-1500 range. As the car warms up and the ECT sensor resistance drops, the ECT sensor becomes controlling and the engine goes to normal idle speed.

I don't know why no one has bothered to do this before and I certainly don't know why I waited so long. I have been saying I was going to do this for years and just never got around to it. But, when my fast idle drifted up to 2100, I said enough is enough!

Hopes this helps someone.

[Brian R.]

Just be sure to eliminate the resistance once the engine heats up so that the ECU gets the correct hot engine temperature.

[artbuc]

Originally Posted by Brian R.

Just be sure to eliminate the resistance once the engine heats up so that the ECU gets the correct hot engine temperature.

Not necessary. When the engine gets to normal operating temp, the ECT sensor resistance is around 0.2 k ohms. The effective resistance which the ECU sees is 0.2 x 1.6 divided by 0.2 + 1.6 = 0.18, well within the allowable error of the ECT sensor.

[Brian R.]

ok, well as long as you've figured this out. Just making sure you were aware of the potential problem.

BTW, nice job!

[artbuc]

Thanks. I drove the car this afternoon and IT WAS A PLEASURE!!! I can't believe how much nicer it is to start a trip in a reasonable fast idle.

[Brian R.]

I will put this in the FAQ thread. Thanks again. When you can, provide a crude wiring diagram of how the resistor was wired.

[artbuc]

I have attached a couple pics and a wiring diagram. I have a 99 Avalon XLS with a 3.0L V6 1MZ-FE engine. My problem is excessive initial fast idle speed at 2100 rpm. Toyota considers this to be in the normal range but I believe it is easier on me and the car to control initial fast idle to 1250-1500. Before making this repair, check your ECT sensor output to make sure it is working ok. Also, make sure all other idle speed controls are functioning normally, eg idle speed ramps up when engaging A/C and idle speed ramps down to 750 +/- as engine warms up to nomal operating temperature. Making this repair will "fool" the ECU into thinking the engine temperature at start-up is warmer than it really is. Once the engine temperature does warm up to normal, the amount of compensation automatically becomes insignificant. The effective resistance (RE) of two resistors in parallel (R1 and R2) is:

RE = R1 x R2 divided by R1 + R2

At 68 degrees, the ECT sensor resistance will be about 2.7 k ohms. If you add a 1.6k ohm resistor in parallel with the ECT sensor, the effective resistance seen by the ECU will be 1.0k ohms. Thus, the ECU will think the engine is 104 degrees and the initial fast idle will be correspondingly lower. In my case it dropped from 2100 to 1250 rpm. In the winter, you may have to slightly decrease the parallel resistor to maintain 1250. When the engine temp warms to normal, the ECT sensor resistance drops to 0.2 k ohms. The effective resistance is 0.18 k ohms which is well within the normal acccuracy of the ECT sensor output. So, the beauty of this solution is that you can set the variable resistor at whatever you need to to get the initial fast idle speed and that compensation automatically eliminates itself as the engine warms up.

[RIP]

Hmm. Great idea. My 4 cyl 06 RAV4 has the same idle "problem" that Toyota says is just fine. Little oil and instantaneous 2100 rpm at startup makes me squirm a bit. Might give this a shot. One of those "why didn't I think of that" things. Great work!

[selfixer]

Originally Posted by artbuc

I have attached a couple pics and a wiring diagram. I have a 99 Avalon XLS with a 3.0L V6 1MZ-FE engine. My problem is excessive initial fast idle speed at 2100 rpm. Toyota considers this to be in the normal range but I believe it is easier on me and the car to control initial fast idle to 1250-1500. Before making this repair, check your ECT sensor output to make sure it is working ok. Also, make sure all other idle speed controls are functioning normally, eg idle speed ramps up when engaging A/C and idle speed ramps down to 750 +/- as engine warms up to nomal operating temperature. Making this repair will "fool" the ECU into thinking the engine temperature at start-up is warmer than it really is. Once the engine temperature does warm up to normal, the amount of compensation automatically becomes insignificant. The effective resistance (RE) of two resistors in parallel (R1 and R2) is:

RE = R1 x R2 divided by R1 + R2

t 68 degrees, the ECT sensor resistance will be about 2.7 k ohms. If you add a 1.6k ohm resistor in parallel with the ECT sensor, the effective resistance seen by the ECU will be 1.0k ohms. Thus, the ECU will think the engine is 104 degrees and the initial fast idle will be correspondingly lower. In my case it dropped from 2100 to 1250 rpm. In the winter, you may have to slightly decrease the parallel resistor to maintain 1250. When the engine temp warms to normal, the ECT sensor resistance drops to 0.2 k ohms. The effective resistance is 0.18 k ohms which is well within the normal acccuracy of the ECT sensor output. So, the beauty of this solution is that you can set the variable resistor at whatever you need to to get the initial fast idle speed and that compensation automatically eliminates itself as the engine warms up.

Will this also reduced the idle after warm up? My 98 V-6 has two ECT sensors on the thermostat according to the Haynes manual. Which one would I splice into?

[dougy1]

popped the wires directly from the plug and soldered in 1.8k ohm resistor...went from 1750 to 1250 rpm's.