Erratic idle on a 2001 Legacy sedan

[freekraz]

Hello all,

 

I have a 2001 Legacy sedan, base model, 5-speed, only 80,000 miles. Recently, the idle has been erratic. Sometimes it dips down below 500 rpm and the car will stall out. Then it will jump back up to standard idle, ~750-800 rpm.

 

The engine check light is NOT on and I can't find any codes with my code reader.

 

I have solved the stalling problem temporarily by raising the idle with the accelerator cable adjustment. Inelegant, but it works.

 

What are some likely culprits? Is there an idle enrichment solenoid? Mass air flow sensor? Another sensor or elecctronic doodad? By the way, before this problem came up, I noticed that when the engine is cold, the idle would often go WAY UP to 2500 rpm plus for the first three minutes running until the engine started to warm. Maybe related?

 

THANKS IN ADVANCE FOR ANY SUGGESTIONS!

 

Jeff in frigid cold Boston

[nipper]

You are way overdue for a timing belt, tensioner, seals, water pump etc. All those parts are every 106,000 miles OR 106 months.

 

Then a good starting point is a tuneup, plugs wires, filter, PCV valve. 

 

From there we could look at the IAC or a vacuum leak, or the MAF sensor. 

[naru]

Clean the IAC.

[freekraz]

Should I clean the IAC or remove and replace? New one $177 at Autozone. Also, what do I have to remove to get at the IAC?

 

Thanks for any tips.

 

Jeff

[Fairtax4me]

Look for any split vacuum hoses first. Also check the breather hoses that run to the valve covers. If you have a MAF sensor it will be at the end of the intake tube with a square top, and a 4 or 5 wire connector plug on the side. I don't think 01 has a MAF though.

 

Does your scanner have the capability to read live data?

If so look at the ECT when the engine is cold in the morning and when it is running as it warms up. Compare the cold temperature with outside air temp, it should be within about 10 degrees. If it reads -40° the sensor is bad or there could be a problem with the connector on the sensor.

Running temp should increase steadily after starting. If it jumps up 15-20 degrees at a time there could be a problem with the sensor.

 

Try cleaning the IAC. There is a style that commonly goes bad that looks like a little can on the side of the throttle body. The valve inside is a cone shape that seats against a port in the TB. Generally very easy to remove and clean, but doesn't always fix the problem.

 

If you have the type that bolts to the top of the throttle body, you'll want to get a new o-ring gasket before removing it.