Back ground info:

2003 Outback sedan with 122K miles. Purchased used about 2k miles ago. Only obvious work is: New battery, alternator and serpentine belt. All fluid levels have remained stable. Using premium gasoline.

 

Problem:

Just last week I noticed that the idle speed would drop when the accelerator pedal was let up. It actually died twice maneuvering in a parking lot. With no throttle input at all it idles smoothly at about 700 RPM. When I got it home to look into the problem I thought that I might not be able to replicate it. I started the car after it had set overnight and I could not get it to lag or die. Gradually as the car warmed up the problem became more noticeable. At operating temperature I could reach underneath the accelerator cables on the passenger side of the throttle body and feather the tab that operates the throttle. Upon let off, the idle speed would sometimes drop for 2-3 seconds then return to around 700 RPM, and sometimes the engine would die before it could return to normal idle.

Several threads point to MAF. Is there a MAF on this intake? Where is it located. If this is not the issue, what else should I look at?

 

 

 

 

Check your vacuum lines and intake hose for leaks.

It could be a simple cracked fitting or loose hose that expands with the heat to make the problem show up.

With the recent work done to it, they could have bumped something or not tightened everything snug.

 

Twitch

no MAF, MAP on our cars I think.

 

kinda wondering about a TPS problem but????

Try cleaning your IAC (idle air control) valve. It's kind of like a choke on fuel injection cars, and if it's not closing properly, it can cause your symptoms. MAF of carb cleaner should do just fine in cleaning it. It's a little solenoid attached to the intake, typically near the throttle body. There is a passage way cast into the intake where it bolts on. Spray your cleaner into that to clean the valve itself. If the solenoid itself is sticking, that will require replacement.

 

Twitch

Try cleaning your IAC (idle air control) valve. It's kind of like a choke on fuel injection cars, and if it's not closing properly, it can cause your symptoms. MAF of carb cleaner should do just fine in cleaning it. It's a little solenoid attached to the intake, typically near the throttle body. There is a passage way cast into the intake where it bolts on. Spray your cleaner into that to clean the valve itself. If the solenoid itself is sticking, that will require replacement.

 

Twitch

I initially dismissed the IACV because he said it idled OK - but it certainly could be gummy and intermittent.

 

good post

Aw crap- did they use the correct alternator? Must be the H6 specific or all kinds of odd stuff happens.

 

This is also a symptom of the throttle position sensor, easy fix to try, about 130 bucks. TPS can be tested in place with an ohmmeter and some patience, two more screws after getting to it to test and it is out.

 

Not sure but the freeSSM software might be able to actually read the TPS position.

The good news:

Cleaned the interior of the throttle body thoroughly with CRC Throttle Body and Air Intake Cleaner (red can). It idles smooth at about 650 and does drop when you let off the gas.

The bad news:

Now the "check engine" light is on. I am guessing I ruined an oxygen sensor in the process. Will pull codes and report back.

 

BTW 

Thanks for the tip on the alternator. 

Codes read and cleared. All had to do with air and fuel intake stuff from starting and running it with all of the air intake duct work off. Runs like new now.