another idle

[tampa]

94 Lx wagon 1.9l. I've read all the idle threads and the one I have only happens when the car is warm and in neutral or park. It does it most of the time but not all and then it will rev up and down. It's slowly gotten worse over the last year. In drive it's fine and still get's great mileage.

[panzees36]

Did you check the TPS?

[A. Souphound]

Originally Posted by tampa

94 Lx wagon 1.9l. I've read all the idle threads and the one I have only happens when the car is warm and in neutral or park. It does it most of the time but not all and then it will rev up and down. It's slowly gotten worse over the last year. In drive it's fine and still get's great mileage.

IMHO the clues given indicate the IAC (Idle Air Control) valve may be sticking. This valve is mounted on the throttle body by two bolts, and can be removed and cleaned with spray can of carburator cleaner. Be careful not to damage the gasket.
There are a number of other possibilities for this condition, you may want to check the PCV also.

[chevyn0va1]

Originally Posted by A. Souphound

IMHO the clues given indicate the IAC (Idle Air Control) valve may be sticking. This valve is mounted on the throttle body by two bolts, and can be removed and cleaned with spray can of carburator cleaner. Be careful not to damage the gasket.
There are a number of other possibilities for this condition, you may want to check the PCV also.

Almost 60.00 here for a new iac around here. btw how can you check/test if its working right?

[A. Souphound]

What I suggested on the IAC is trying to isolate the problem to the IAC.....looking for a change in idle. A sticking EGR valve, fuel injector, among other components will give the same indication. The poster didn't give any history or particulars on maintenance, mileage etc.
To answer your question, correct operation is determined by engine performance. The IAC motor is not inoperative because it operates some of the time and the idle is normal. Follow me?

[chevyn0va1]

Originally Posted by A. Souphound

What I suggested on the IAC is trying to isolate the problem to the IAC.....looking for a change in idle. A sticking EGR valve, fuel injector, among other components will give the same indication. The poster didn't give any history or particulars on maintenance, mileage etc.
To answer your question, correct operation is determined by engine performance. The IAC motor is not inoperative because it operates some of the time and the idle is normal. Follow me?

I follow. I have a personal peeve with my car. A post I had before says its normal for this model car. Problem is when at an idle, stop or drive thru the cars idle down so much so I always think its going to stall but it never does. Then it goes up to normal and I never had a car with a computer. It could be I'm just noticeing the computer correcting itself.

[toolman11]

I have a '97 LX and have the same idle problem. But, I only have that problem in spring and fall when the temperature outside is a few degrees above freezing. When the car is cold it runs fine but after it warms up the idle on neutral is up and down. This will last about a month until the outside temperature is over 10 or 15 degrees Celcius. In the cold of winter or the heat of summer it runs fine. This has been going on for 2 years now. I have never had the car properly checked. It does not affect power or fuel consumption.

[A. Souphound]

Originally Posted by toolman11

I have a '97 LX and have the same idle problem. But, I only have that problem in spring and fall when the temperature outside is a few degrees above freezing. When the car is cold it runs fine but after it warms up the idle on neutral is up and down. This will last about a month until the outside temperature is over 10 or 15 degrees Celcius. In the cold of winter or the heat of summer it runs fine. This has been going on for 2 years now. I have never had the car properly checked. It does not affect power or fuel consumption.

It sounds like the O2 sensor is slugglish or the O2 sensor heater may be faulty. Here is my rationale:
When the engine/outside temperature is cold the air/fuel mixture is operating on a computer 'default' (open loop) setting. The exhaust temperature and the O2 sensor has to reach approx. 700F before it starts sending signals to the computer, and then the computer controls the fuel/air ratio and timing. The computer is also sending commands to the IAC, and the constant change from rich/lean/rich causes the engine to 'lope' In most cases, I have found by replacing the O2 sensors and cleaning the IAC cures the problem. Of course the 'root cause' of the problem is the engine is not burning as clean as it should (Plugs/Wires) or a leaking manifold/exhaust gaskets and age will affect the O2 sensors.