idle drops then stumbles, undriveable

[brd]

Here's what's going on with my 97 Legacy Outback.

It idles high all the time. Around 1100rpm in gear.

On a warm start, there are 2 scenarios:

#1 if the idle goes up to 2000rpm and I shift into Reverse or Drive pretty quickly, I can drive around for an indefinite length of time.

#2 Sometimes when you start it, the revs don't climb that high, but maybe to 1500. Then they will drop below 1000rpm and shudder quite a bit. Trying to shift into R or D then and the car bucks and shudders. When this happens, I turn it off and restart and hope for case #1.

If you start it and #1 happens, but leave it in P or N for more than 5-10 seconds, idle will drop and go into the 2nd scenario.

If you have #1 and then drive around for say 30minutes or an hour, but then shift into P or N, after 5-10 seconds idle will drop and it will go into 2nd scenario. But restarting the car can fix it.

I have replaced the Neutral Switch (also called the Inhibitor Switch) and the IACV. I have cleaned the MAF sensor. It has thrown a couple codes, the latest was P0507 Idle Control System RPM higher than expected. (It also threw a P1507 in the past). I have done my best to check for vacuum leaks. Also have cleaned the battery grounds and had the battery tested.

Any ideas. If I can't fix it soon, my wife is going to make me take it to the shop.

[nipper]

How many miles on this car?
Any work done recently?
Was this problem there before you did the other work?
Have you checked for loose vacume lines?

[brd]

How many miles on this car?
Any work done recently?
Was this problem there before you did the other work?
Have you checked for loose vacume lines?

125000 miles. No other work done. Just threw a CEL one day and I've been fighting this thing since.
Have done my best to check for vacuum lines. Traced all the ones I could see, wiggled them with the car running, and sprayed carb cleaner around them, but didn't find anything.

Do you need to recalibrate anything when installing the new IACV?

[nipper]

No recal needed. What code has the puter thrown. If the codes havent been read, they need to be.

Sometimes a bad o2 sensor can cause this.

nipper

[subba]

bad o2 as nipper said, or maf

[decke48]

bad o2 as nipper said, or maf
add tps to that list also

[brd]

No recal needed. What code has the puter thrown. If the codes havent been read, they need to be.

Sometimes a bad o2 sensor can cause this.

nipper

P0507, P1507. Never had any codes that indicate O2 or MAF, but I guess it's worth checking out. I'm just tired of throwing parts at the problem.

[nipper]

No recal needed. What code has the puter thrown. If the codes havent been read, they need to be.

Sometimes a bad o2 sensor can cause this.

nipper

P0507, P1507. Never had any codes that indicate O2 or MAF, but I guess it's worth checking out. I'm just tired of throwing parts at the problem.

Whenever you get multiple codes, look for a common denominator, just like math.

One code is a Idle control system RPM higher then expected (basically a "i'm not expecting that" light from the computer). 1507 is putting the Idle Air control in failsafe. That measn the car has tried to control the idel air control, and nothing is working.

So next you have to look at what effects the engine idle directly. You have enough mileage on this car to have a tired O2 sensor (not ready to throw a CEL but on its way out). Replace it with a OE sensor (especially since you have an issue). This wont be throwing away money. The O2 sensor is the nose of the car adjusts the air/fuel mix as needed. If it is out of wack it can try to compensate either way and make the idle screwy.

On the other side of the equation can be a vac leak or an exhaust leak before the O2 sensor. Again too much air and the O2 tries to compensate. I doubt a tps as that would be a stumble. A air mass sensor may be possible, but that is rare on these cars *yes they go bad but its not often).

Hope that helps.

nipper

[brd]

Well, I ended up taking it to an indy shop. They diagnosed it as a leaking intake gasket. Called today and told me it was fixed and the tps adjusted and it's running good now. We'll see when I go pick it up this afternoon. The total is $366. I figure that's gotta be better than the stealer would do.

[ScaryFatKidGT]

intake gasket??? like by the TB? or between the intake manifold and the block?

whats an intake gasket?

[brd]

Manifold.

[Huffer]

So was the problem fixed? I honestly would have thought bad MAF - the intake manifold gaskets don't usually go bad unless the IM has been removed.

[brd]

So was the problem fixed? I honestly would have thought bad MAF - the intake manifold gaskets don't usually go bad unless the IM has been removed.

Yes, the high rpms are fixed as is the drop in rpm & stumble when in park or neutral.

The car had a reman longblock 20k miles ago, so maybe the gasket was messed up then and just blew out.

Still had a CEL show up today, but the guy said this is residual as the computer tries to "relearn" a new map for the new tps settings and airflow. He said to drive 300 miles and then he would clear it, otherwise it would just come back. :-?

[Huffer]

^^ the guy is incorrect. CEL's show up because the stock base map doesn't work for some inconsistencies and the ECU cannot learn around it.
Which means it will never learn around it and the CEL will always come back.

[decke48]

if the code comes back. the fix wasnt the cause. plus intake leak usally trick a high/low fuel trim code because air/fuel calculations are not right.. if you can try checking the gap between the tb plate and body it should be .035 inch