My Suby has an erratic idle and P0400 code popped

[subdog1]

I'll start from the beginning, I noticed my 95 Legacy wagon w/2.2 had a fast idle. So fast that I didn't need to apply the pedal to get moving. About a week later, it throws a P0400 code. I removed the EGR and cleaned. I checked All of the vaccum lines and everything looks good. I haven't checked the tube running from the egr valve body to the #4 cyl head yet but that's on the list. So after I cleaned and installed the EGR, The idle became erratic then seemed to level out. Now the Idle is up again. I took the breather tube off the throttle body and inspected the butterfly. It looks pretty good with a slight amount of carbon build up on the edges. I'm taking off the throttle body tomorrow to do a good clean job. Could the egr system be causing an erratic idle? Any ideas on what to check?? I've been running for about 2 weeks without any codes but the idle problem has me stumped.

Thanks for the help.

[anothernord]

The EGR should be closed at idle, if it isn't it will idle like crap or even stall out. You can test if its open or not by letting the engine idle, and pushing the metal piece of the diaphragm. If you can move it and the engine starts to idle worse, then release and it gets better, then its probably not the EGR.

[subdog1]

I tested the EGR by adding vaccum directly to it and it operated normally. The engine did start to die down as vaccum was added at idle. I can't figure out why it wants to idle so high. The only thing I can think of is the butterfly is sticking open slightly causing a higher idle. I'll keep checking.

Thanks for the reply.

[green97gt]

vacuum leak?

[anothernord]

I tested the EGR by adding vaccum directly to it and it operated normally. The engine did start to die down as vaccum was added at idle. I can't figure out why it wants to idle so high. The only thing I can think of is the butterfly is sticking open slightly causing a higher idle. I'll keep checking.

Thanks for the reply.

At idle, the throttle butterfly valve is totally closed, and the IACV opens to allow air into the manifold. Unfortunately, the IACV is totally computer controlled. You might want to clean it out.

[subdog1]

I did check all the lines for cracks or loose connections and haven't found any problems in the vaccum system. I haven't checked the IACV but I'll take a look at it. Is this a common problem area where build up occurs?

[anothernord]

I did check all the lines for cracks or loose connections and haven't found any problems in the vaccum system. I haven't checked the IACV but I'll take a look at it. Is this a common problem area where build up occurs?

Yes, the IACV does get dirty and eventually the idle will suffer.