2000 Legacy w/rough idle..occasionally stalls..help!!

[Diesel]

Hi all,

I purchased a 2000 Subaru Legacy Sedan with automatic transmission and 121K for my daughter. The car was well maintained by previous one owner using only Subaru dealers. The head gasket was replaced at 90K along with the timing belt at 100K.

A few weeks ago my daughter said the car would run rough at idle and occasionally stall when she started up. This along with a noticeable lack of power going up hills. She would sometimes run the gas tank very low so I decided to change the gas filter, spark plugs and wires, PVC valve and air filter. The end result was the same symptoms.

Any suggestions would be greatly appreciated.

Thanks Bob K

1997 Subaru Outback 105K
2000 Subaru Legacy 121K

[bheinz57]

You have replaced the right things so far. What about the coil pack? Is/was there any corrosion on the ends when the plug wires were changed? Do you know if the coil pack has ever been changed?

How about check engine lights?

Sufficient battery/alternator?

Brian

[jellisii]

Originally posted by Diesel
Hi all,

I purchased a 2000 Subaru Legacy Sedan with automatic transmission and 121K for my daughter. The car was well maintained by previous one owner using only Subaru dealers. The head gasket was replaced at 90K along with the timing belt at 100K.

A few weeks ago my daughter said the car would run rough at idle and occasionally stall when she started up. This along with a noticeable lack of power going up hills. She would sometimes run the gas tank very low so I decided to change the gas filter, spark plugs and wires, PVC valve and air filter. The end result was the same symptoms.

Any suggestions would be greatly appreciated.

Thanks Bob K

1997 Subaru Outback 105K
2000 Subaru Legacy 121K

Vacuum leak? Easy way to search for it is with a can of carb cleaner and hose down the engine bay.

Bheinz57 has good suggestions: CEL would be a dead giveaway. Could be a failing sensor, but usually that'll set a CEL. Not always, but usually. Nipper could tell you more about that than I could, as I haven't studied the arcana of this particular car's electrical system yet.

Pressure testing the cylinders would be a good idea, but only if you have easy access to the tool. The gasket may have failed again.

Could be gummed up injectors as well, but it sounds too intermittent for that.

Is it worse when the engine's hot/cold?

[Diesel]

The problem is worse when the car is warmed up. I cleaned the Throttle Body and also ran fuel injector cleaner in the last two tanks of gas. I was planning on today trying to check for a vacuum system today with carb cleaner.

Thanks for the replies and suggestions....keep them coming!

Bob

[porcupine73]

Hi Bob!

A few questions / notes
1. Is the check engine light / CEL on?

2. Does it seem to run ok above idle, like while cruising (other than the power loss on hills).

3. If it seems to run ok above idle, but poorly at idle, I would clean the IACV idle air control valve. To do that on that soob, remove the air filter and air filter box. Then with engine idling, spray short blasts of throttle body cleaner up at the top of the intake above the butterfly. This is where the IACV intake is on that style. Give it a couple dozen blasts, like spray 1/2 second, engine will stumble, then when it reocvers, give it another shot. See pic at end of post for IACV intake pic.

4. When you cleaned the throttle body, did you remove the throttle body, or clean it in place?

5. For power loss, check the knock sensor. This thing may not cause the CEL to illuminate but it can definitely result in severe power loss; I have experienced this on a few soobs.

6. Soobs of that era like NGK spark plugs and OEM spark plug wires, and can develop misfire and other odd issues if anything else is used, esp cheap parts store wires.

[snowon]

O2 sensor perhaps? or would that make it run bad all the time?

[Diesel]

The CEL is not on. I put a reader on anyway and there were no codes.

There is no issue at all above idle. Runs smooth on the road. In fact when I stopped at a light it would idle ok at first then it would start to pulse. This would not occur at every stop. Only occasionally will it stall.

I cleaned the throttle body in place. Is there a better way?

Great diagram and suggestions! This has to be one of the best lists for help. I will be busy today with your help and will advise of my progress.

Bob

[Diesel]

Hi all,

Finished for the day...not fixed but hopefully getting closer. Here is what I did:

Removed idle air control valve, it was dirty so I cleaned and replaced. Same problem.

Tried in vain to find any vacuum leak, no sign of one.

Someone said that if I unpluged the Throttle Position Sensor and the problem disappeared then that could be it. I unplugged it and set off the CEL with 8 codes, but only made a slight difference. What is the TPS and chances the problem is that?

I called a Subaru Dealer for the price of a new Idle Air Control Valve and hold on to your hats they quoted $380.00. So swapping out new parts is out of the question at this point. I did go on ebay and a low mileage used Throttle Assembly which includes the IACV and sensor (Throttle Position Sensor) is about $150.00.

What is the thought on trying used sensors, IACV and throttle assembly? Is this foolish at his point?

Bob

[cougar]

To be on the safe side, you may want to check your timing belt and make sure it hasn't jumped a tooth. It is easier to check than repair an engine. Cheeper too.

[jellisii]

Originally posted by Diesel
Hi all,

Finished for the day...not fixed but hopefully getting closer. Here is what I did:

Removed idle air control valve, it was dirty so I cleaned and replaced. Same problem.

Tried in vain to find any vacuum leak, no sign of one.

Someone said that if I unpluged the Throttle Position Sensor and the problem disappeared then that could be it. I unplugged it and set off the CEL with 8 codes, but only made a slight difference. What is the TPS and chances the problem is that?

I called a Subaru Dealer for the price of a new Idle Air Control Valve and hold on to your hats they quoted $380.00. So swapping out new parts is out of the question at this point. I did go on ebay and a low mileage used Throttle Assembly which includes the IACV and sensor (Throttle Position Sensor) is about $150.00.

What is the thought on trying used sensors, IACV and throttle assembly? Is this foolish at his point?

Bob

This is all off of the top of my head, and could be completely wrong, so check my facts.

It's possible that a TPS could cause your problem, but off the hip, I don't think that it would be, without setting a CEL. What it does is sends a signal to the computer to let it know how far you're mashing the throttle with your lead foot. The computer combines this reading along with the manifold air pressure (MAP) sensor and current RPM of the motor to calculate how wide to set the fuel injector pulse width. I don't have a lot of experience with the Subaru computers, but I suspect that it's what's called a "closed loop" system, meaning it reads the output of the o2 sensor in combination with the above to even further refine the mixture.

Typically when the TPS fails, the sensor fails in a "full open" i.e. all throttle all the time mode. This is typically by design, to allow you to be able to drive the vehicle home. When it fails in this manner, the computer will typically set a CEL because none of the other readings (tach, o2, MAP) are agreeing with the TPS at that point. The car will typically run very rich as well, which would make it seem that it is down on power, but it would also belch black smoke as well. This would also set a CEL because the 02 sensor would freak out because the car is running rich. This is probably part of the reason it set 8 codes as you mentioned when you disconnected it.

I don't think the TPS is your problem. I don't know how much they go for, and if they're cheap, it's worth a shot, but I don't think this is your problem.

Cougar brings up a good point. You have an inspection hole for the right side, and the timing gear cover comes off easily on the left side. Might be worth looking into it, but I'd think you'd have other problems if the cam timing had jumped.

I'm out of ideas currently. I was almost certain that you'd find a vacuum leak.