Hello Gents!

 

I have having some issues with my 2005 Impreza RS. When I slow down I sometimes feel a shudder in the vehicle. It also sometimes shifts pretty hard between gears.

 

When the hard shifting started I looked into and replaced the transmission with one that had 27k miles on it. No change in the problem.

 

Thoughts?

How many miles on the car? Auto or manual transmission?

Did the shuddering occur before replacing the transmission?

Any other details you can give about the problems?

Does engine temperature affect either symptom?

1.) About 165k. Automatic Transmission

2.) Yes. The shuddering and hard shifting it what prompted me to look into a replacement.

4.) I believe I feel it more often after the car is warmed up and driving around

 

3.) Side note to all this fun stuff. I replaced the spark plugs on monday and now the car is idling abnormally low. On my way into work today the CEL came on with code P0506. This car is driving me nuts!

 

Thanks for any information you can provide.

Edited June 13, 201312 yr by SoulForge

P0506 Idle air control system, Rpm lower than expected.

This code means there is a vacuum leak or other problem causing a low idle speed condition for which the IAC valve is not able to adjust far enough to correct.

This could be because of a faulty IAC motor, or the valve for the IAC is clogged.

Since this code occurred after changing spark plugs you should inspect the hoses for the breather system that attach to the intake piping. There should be one from each valve cover and one that attaches to a Y next to the hose from the PCV valve. The PCV valve should be next to the throttle body on the passenger (right hand) side of the intake manifold.

Also check all of the small vacuum hoses that attach to the intake manifold. You may have one that is broken or split, which could be causing the shuddering issue. There are a few that loop under the intake manifold on each side of the engine that go to solenoids for the EGR and Evap systems.

 

I would also recommend removing the IAC valve and cleaning it as well as the ports in the manifold. While you're at it, clean the bore of the throttle body as well as the back side and edges of the throttle plate. I just use a rag soaked in Throttle body and Air intake cleaner (Can be bought at any auto parts store) to wipe the crud off. Spray the cleaner into the IAC and let it soak for a minute or so to help dissolve the crud in there.

P0506 Idle air control system, Rpm lower than expected.

This code means there is a vacuum leak or other problem causing a low idle speed condition for which the IAC valve is not able to adjust far enough to correct.

This could be because of a faulty IAC motor, or the valve for the IAC is clogged.

Since this code occurred after changing spark plugs you should inspect the hoses for the breather system that attach to the intake piping. There should be one from each valve cover and one that attaches to a Y next to the hose from the PCV valve. The PCV valve should be next to the throttle body on the passenger (right hand) side of the intake manifold.

Also check all of the small vacuum hoses that attach to the intake manifold. You may have one that is broken or split, which could be causing the shuddering issue. There are a few that loop under the intake manifold on each side of the engine that go to solenoids for the EGR and Evap systems.

 

I would also recommend removing the IAC valve and cleaning it as well as the ports in the manifold. While you're at it, clean the bore of the throttle body as well as the back side and edges of the throttle plate. I just use a rag soaked in Throttle body and Air intake cleaner (Can be bought at any auto parts store) to wipe the crud off. Spray the cleaner into the IAC and let it soak for a minute or so to help dissolve the crud in there.

 

Thanks for the information. I am not the greatest mechanic in the world as I am still learning. What does the IAC look like? 

 

I have been trying to find a blow out view of the engine and its parts and not having much luck with that.

 

Edit; Information I am seeing is that my 2005+ car doesn't have an IAC....is this the case?

Edited June 13, 201312 yr by SoulForge

Doh! 2005 is when they changed everything. You are correct, that year has an electronic throttle body which controls idle speed without the use of a separate IAC valve.

The throttle body can still be gummed up with carbon/oil sludge crud and need cleaning though. If the throttle valve is sticking to the bore in the closed position it can cause fluctuations in idle control when coming to a stop or slowing down.

 

The EGR went all electronic that year as well, so there will be no vacuum hoses going to that.

They appear to have moved the Evap solenoid to the front of the manifold in the center (maybe a little off to the left), so be sure to check the vacuum hoses leading to that.

The PCV hoses are routed differently as well, but there will still be a hose to each valve cover that hook to a series of pipes on top of the intake manifold, and eventually lead into the manifold. Be sure to check over all of those hoses for proper connection. Also check the ends for splitting.

 

The best place to find exploded views of the various engine components is opposedforces.com. Click on parts catalog and use the drop-down menus to select your vehicle.

That website does not resolve for me. Typo?

 

Worked the 2nd try.

Edited June 13, 201312 yr by SoulForge

Fairtax. I drove my vehicle in today and cleared the CEL after I got to work. The idle didn't dip down like it has been. ECU adjustment?