1997 4Runner SR5 - Idle Problems

[werminghausen]

I have the same problem. If I put it in drive and let it idle down the road, it still does it. At a stop light I have to keep my foot firmly on the brake.

Hi Sawguy,

seems we both are the only ones on the planet having this issue with the idle
doing what it wants... idling high (1600 ish)..then all of a sudden (after maybe 1 minute) go down to 1000, then back up to 1600...and so on.
The stepped idle mode is making me wonder if the idle air valve is working? Yes i think it is working and doing the steps...just the input signal seems to be off?


best, Martin

 

[jreask]

Possibly the coolant temperature sensor? Have you checked it?

 

[werminghausen]

I did not do anything on the engine. I wanted to survive this winter badly and then do the timing belt with new plugs and new temperature sensor.

I was now studying a bit the ECU

Key Engine Control Unit Input Signals

1) Engine Load
Computed from Air Flow Rate into the engine and Intake Manifold air pressure

2) Engine Speed
Reported by the Crankshaft Position Sensor

3) Coolant Temperature
Reported by the engine coolant sensor, a thermistor that varies its resistance according to the engine coolant temperature

4) Throttle Position
Throttle position sensor creates a voltage signal that varies in proportion to the throttle valve opening angle

5) Intake Air Temperature
Measured by another thermistor located in the Mass Air Flow Sensor unit

6) Battery Voltage
Battery voltage affects the speed at which the fuel injectors open and must be taken into account in computing the fuel injector pulse length, or injector open time

7) Oxygen Sensor
The oxygen density in the exhaust emissions is detected and generates a control signal back to the ECU indicating the burned air/fuel ratio.


So each one of these sensors might have some influence on my bad idle...and how shall I start? So far I did not find out what sensors influence the operation of the Idle air valve.

As I got lately also a Check Engine light I ordered a OBDII, pretty cheap . Maybe there is some information revealed what is wrong with this engine.


Martin

 

[werminghausen]

In the meanwhile I got the check engine light: lime to buy the OSBII.
The code was the one for the temperature sensor

I just changed the temperature sensor behind the timing belt cover.
What a difference! Now the engine idles at 600/650 as it should.
It seems that this sensor is to consider if idle is too high and going up and down. Mine went from 1600 to 1400 to 1000 and right back to 1600 where it mostly stayed.

I think the problem is solved!

Best, Martin