Diagnosing Idle Surges on Subaru Legacy Models - Engine Builder Magazine

Diagnosing Idle Surges on Subaru Legacy Models


By Eric Seifert

ALLDATA Automotive Technical Editor

Steve enjoys mountain biking, and his 2001 Subaru Legacy has no problem getting him to the mountains and back. Yet it doesn’t like to commute. Steve called me after work one day to inquire about a surging problem the Legacy has had for a while. He said that the car would surge in low-speed traffic, especially after reaching operating temperature. We scheduled an appointment and I did some research. I discovered that the surging problem is common to some newer model Subarus.

If your customer encounters a driveability concern such as idle surges or whistling, it may be caused by carbon buildup on the Idle Speed Control (ISC) valve. In these cases, it is not necessary to replace the ISC valve. Cleaning the ISC valve could correct the condition. To clean an ISC valve, perform the repair procedure.

Applicable Vehicles

1999 Legacy 2.2L CAL

2000-’01 Legacy 2.5L MT

All Legacy 3.0L MT

2004 Baja 2.5L Turbo

1999 Impreza 2.2L CAL

2000-’01 Impreza 2.2L

2002-’04 Impreza 2.0/2.5L Turbo

REPAIR PROCEDURE

Normally Aspirated Vehicles:

1. Warm up the engine.

2. On 2.2L/2.5L engines only, remove the bolt that attaches air cleaner case B to the bracket. See Figure 1. Undo the three clips that hold together air cleaner case B to air cleaner case A. Remove air cleaner case B and the air cleaner element and set aside. (On all 3.0L H6, remove the entire air intake chamber).

3. Start the car and maintain engine speed between 1,000 and 1,500 rpm.

4. Spray engine cleaner (GM P/N 12345089 GM Top Engine Cleaner or equivalent) toward the upper air-stream of the throttle chamber for approximately 10 seconds.

5. Stop the engine and let it sit for three minutes.

6. Restart the engine and maintain 1,000 to 1,500 rpm.

7. Spray engine cleaner on the upper air-stream of the throttle chamber for approximately 10 seconds.

8. Turn off the engine.

9. Reinstall the air cleaner element and air cleaner case B.

10. Operate the car between 1,000 and 2,000 rpm until no white smoke appears through the tailpipe.

11. Turn off the ignition switch and clear the memory.

For Turbo Vehicles:

1. Warm up the engine.

2. Remove the intercooler (see Figure 2) and set aside.

3. Disconnect the mass airflow (MAF) sensor connector.

4. Cycle the key “on/off” once (to enter “failsafe” mode).

5. Start the car and maintain engine speed between 1,000-1,500 rpm.

6. Spray engine cleaner (GM P/N 12345089 Top Engine Cleaner or equivalent) on the upper air-stream of the throttle chamber for approximately 10 seconds.

7. Stop the engine and let it sit for three minutes.

8. Restart the engine and maintain 1,000 to 1,500 rpm.

9. Spray engine cleaner on the upper air-stream of the throttle chamber for approximately 10 seconds.

10. Turn off the engine.

11. Reinstall the intercooler and reconnect the MAF sensor connector.

12. Operate the car between 1,000-2,000 rpm until no white smoke appears through the tailpipe.

13. Turn off the ignition switch and clear the memory.figure 1

Written by ALLDATA Technical Editor Eric Seifert, an ASE certified Master Technician and Engine Machinist, with 20 years of independent shop and parts store experience.

For additional information, visit www.alldata.com.

 

Additional Tech Tips>>

Figure 2

You May Also Like

Shop Solutions February 2023

Check out February’s shop tips and tricks.

Engine and machine shop tips and tricks.

Dowel Removal

This is an easy and clean way to remove hollow dowel pins found in connecting rods or mains. Start tapping the I.D of the dowel with an NPT tap. Once it starts to cut, it will spin the dowel, and with upward pressure, the dowel can be removed and reused.

Shop Solutions January 2023

Next time you have set of large journal small block Chevy connecting rods to resize, consider honing the big ends of them for a +.002” outside diameter bearing that the LS engines with fracture cap rods use.

Shop Solutions December 2022

Everyone misses occasionally, and this helps avoid dents and damage.

November 2022 Shop Solutions

November tricks and tips for the shop!

Shop Solutions October 2022

When machining on the CNC mill, it’s necessary to blow the flood coolant and chips off the parts for inspection. I tried a tool holder mounted fan, but it wouldn’t get all the chips and coolant out of the deeper areas.

Other Posts

September 2022 Shop Solutions

September tricks and tips for the shop!

Shop Solutions
August 2022 Shop Solutions

August tips and tricks for the shop!

Shop Solutions July 2022

When the timing cover or block has no dowel pins, or the dowel holes do not fit snug on the pins. Take an old damper and hone the center so that it is now a slip fit onto the crank snout. Use it to hold the cover in place while tightening the bolts.

Shop Solutions June 2022

I needed a narrow grooving tool to quickly clean carbon from piston ring grooves for an engine restoration project. All the usual grooving tools were too wide.