My 99 2.5 automatic runs great and has had all tuneup stuff done with factory parts. I cleaned the IAC valve per the service manual procedure and before and after it reacts to putting the air conditioning on and off, so I believe it is working at least partially. Problem is idle speed looks to be about 600 RPM by dashboard tach when stopped in gear. There is quite a bit of shudder, which a slightly higher idle speed would correct. Is there some other input to the computer which may be in error which could cause this?

I think "normal" is between 6-800 rpm. Mine usually hangs between 6-700.

I am not sure what the idle speed should be. What's odd on this car, is it started to shake at traffic lights after I replaced the driver side front drive axle due to a torn boot. I can't imagine how that could affect anything, but the shake came all of a sudden, and it's very noticable. It feels like the car could stall as a result of it.

both the legacys we have idle at 650...when I had a dirty iac it caused a high idle around 1000. Yours doesnt sound low just rough...have you changed the plugs and wires recently? If not, might start there. Is this an auto? If so, does putting it in neutral at stop lights "cure" the shudder. If so there is a transmission problem...start with flushing the fluid. Good luck.

What's odd on this car, is it started to shake at traffic lights after I replaced the driver side front drive axle due to a torn boot.

That is not odd. There are numerous posts about vehicles deveoping this odd vibration when stopped in drive after replacing axle half shafts with aftermarket units.

 

The proper idle speed range should be listed on an underhood sticker.

That is not odd. There are numerous posts about vehicles deveoping this odd vibration when stopped in drive after replacing axle half shafts with aftermarket units.

 

The proper idle speed range should be listed on an underhood sticker.

 

 

I USED to have bad shudder at idle in gear. Now it is GONE! Happy, happy, joy, joy. :banana:

 

I did many things to try to fix. Tranny flush, twice, IAC clean, then swap, throttle body clean, new plugs. Nothing worked.

Then the shortblock died due to rod bearing failure. So I got a Phase II shortblock and used the motor mounts from my Impreza. All is good now. I can hardly tell when the motor is running now and it idles at about 500rpm.

 

So try the motor mounts. If that doesn't work, try the motor. It doesn't appear to be tranny related. My 2 cents.

What's odd on this car, is it started to shake at traffic lights after I replaced the driver side front drive axle due to a torn boot.

 

That is not odd. There are numerous posts about vehicles developing this odd vibration when stopped in drive after replacing axle half shafts with aftermarket units.

 

Ditto.

 

I had the same problem with my car. The replacement half shaft was a Subaru re-manufactured one. The vibration was slight, but there. They changed it again under parts warranty and it was much better; almost back to original, but not quite.

 

I later had the other side done and it was fine. Again, perhaps just a hint of increase in vibration, but tolerable.

 

If you did the half shaft yourself, you could try rotating the connection at the differential by 90 degrees or 180 degrees. I've heard of that solving the problem, but it's a crap shoot.

 

Several years ago when my engine was replaced, I had them put in the newer liquid filled mounts. They probably help to diminish vibrations a bit. I did that at the time because I had installed a lightweight crank pulley and vibration increased a bit as a result of that. The mounts helped quell things.

 

Commuter