2000 Subie Outback, 4 cylinder engine, auto 105K miles. During acceleration, it sometimes loses power. The tach needle jumps up and down for 30 seconds +/-. It doesn’t happen often, and our mechanic can’t figure it out. Neither can we.
In order to try–from afar–to help you figure out this problem, we need more information from you.
First–when “The tach needle jumps up and down for 30 seconds”–does the speed of the car increase at all?
If not, you could well be looking at a transmission problem.
In addition, you also need to tell us what the car’s maintenance history has been (in detail) over the past 3 years, and you also need to tell us what repair attempts your mechanic has attempted–whether they have been successful or not.
You also need to tell us if the Check Engine Light ( CEL) is illuminated, and if so, what trouble codes have been found.
And, even though it has nothing to do with the problem that you mentioned, I have to ask whether the timing belt has been replaced. At 105k miles, it is due on the basis of odometer mileage, and it is grossly overdue (by about 4 years) on the basis of elapsed time. If you have not yet replaced the timing belt, you are in store for MUCH bigger problems than an erratic engine speed.
Please respond with details in order for us to try to help you.
VDCdriver should be commended for his patience.
This car is 13 years old and has been driven over 100K miles. If you don’t tell anyone anything at all about the basic condition of the car’s maintenance why would anyone know where to start? In addition its been to a mechanic who has apparently done a bunch of stuff. Wouldn’t you presume we’d all start by saying to do the same stuff? So…you need to fill folks in.
Just a guess but check the alternator for excessive noise. Also check and clean the ground connections on the transmission and the engine.
I don’t see it as an alternator problem. Neither do I see it as a grounding problem. At least that’s not where I’d start.
Where I’d start on this car is a basic tune-up. A new air filter, new spark plugs, and setting the ignition timing. If there’s any cracking in the high voltage wires, I’d replace those too. Until all that has been done, it is hard to say what is happening. Loss of power on acceleration can be a symtom of retarded ignition timing.
If a tune-up has already been done and the timing is correct, the next place I’d look would be the fuel and emissions systems. A clogged fuel filter could cause this symptom for example.
If I had an auto repair shop I think I’d hang a big poster on the wall covered with the 1001 things that could go wrong with how a car runs. Every time someone brought a car in, I’d assign a mechanic. S/he’d stand at about 20 paces with a blindfold, spin around three times, and throw a dart. The dart would choose the diagnosis.
I’m pretty sure that’s how most of the shops I’ve been to do it, anyway.
Hi,
First–when “The tach needle jumps up and down for 30 seconds”–does the speed of the car increase at all? If not, you could well be looking at a transmission problem. <<
The speed of the engine and the car goes up and down with the tach needle. So, the car is lurching a little bit when it loses power. It’s not dramatic, but it’s real.
The transmission was rebuilt about a year ago, so I did ask the the transmission guy to check it again, and he found no problems.
In addition, you also need to tell us what the car’s maintenance history has been (in detail) over the past 3 years, and you also need to tell us what repair attempts your mechanic has attempted–whether they have been successful or not. <<
The car has been consistently maintained, including the periodic inspections, replacement of parts that wear, etc., although we have not washed the car as often as we should. 
Except for rebuilding the transmission about a year ago, the maintenance has been unremarkable.
You also need to tell us if the Check Engine Light ( CEL) is illuminated, and if so, what trouble codes have been found. <<
The check engine light did come on once. The mechanic checked it out, said the trouble code was a clogged fuel filter, which he replaced, and he cleared the code. The last few times the problem occurred, the check engine light did not illuminate.
And, even though it has nothing to do with the problem that you mentioned, I have to ask whether the timing belt has been replaced. At 105k miles, it is due on the basis of odometer mileage, and it is grossly overdue (by about 4 years) on the basis of elapsed time. If you have not yet replaced the timing belt, you are in store for MUCH bigger problems than an erratic engine speed. <<
We replaced the timing belt about 2 years ago.
This car is 13 years old and has been driven over 100K miles. If you don’t tell anyone anything at all about the basic condition of the car’s maintenance why would anyone know where to start? In addition its been to a mechanic who has apparently done a bunch of stuff. Wouldn’t you presume we’d all start by saying to do the same stuff? So…you need to fill folks in. <<
I had to rewrite the first message I left due to a problem with the web site (it told me I had 38874 too many tags, which wasn’t accurate).
As noted above, the car has been otherwise unremarkable.
As for the mechanic, except for the check engine light and replacing a fuel filter, he said he checked the charging system and other systems, and he could find no problem. I don’t know exactly what checks he did.
Where I’d start on this car is a basic tune-up. A new air filter, new spark plugs, and setting the ignition timing. If there’s any cracking in the high voltage wires, I’d replace those too. Until all that has been done, it is hard to say what is happening. Loss of power on acceleration can be a symtom of retarded ignition timing. <<
As part of his review, I think the mechanic checked the timing. He did not do a tune-up.
Thank you all for all of your suggestions, I appreciate your help.
First off, there is no code for a clogged fuel filter… Does not exsist… So I am going to make a guess that you have a fuel related issue. This is a very tough one to Diag since the car does not do it all of the time. I would try having a fuel pressure gauge hooked up and try to have the car act up, see if you are looseing pressure at that time. On the flip side you may want to try spraying down your ignition system with water and see if you are arching out somewhere some times causeing a miss (which should thow a code, but may not).
gsragtop’s suggestions are good ones. He’s also right about the check engine light. See if you can dig up an invoice or something with an actual code printed on it. It would look like “P1234” What you will likely find is that it is a report of an error that could be caused by a clogged fuel filter…among many other things.
You might also ask the mechanic whether or not his scanner will pick up things called “pending” codes. They are stored when the computer is “almost ready” to declare something and issue and turn on the check engine light.
The question about maintenance is a question about specifics. People mean all sort of things by “consistently maintained” or “well maintained.” But often what they mean is that they regularly run through a quickie lube for an oil change & check of fluids. How old are your spark plugs & wires? Air filter? We’ll assume the fuel filter was replaced. What kind of shop rebuilt the transmission? Do you know any of those details? (There are somewhat different things that people might call “rebuilding” a transmission). Did the rebuild also come with a new torque converter? Or is it still the original? What happened that led to the rebuild? Was it ever serviced before that? (e.g. fluid/filter change?)
This is a Subaru. A knowledgeable mechanic should evaluate it for a possible head gasket breach.
However, thus far the info isn’t enough to point at anything with more confidence than another. You could be having problems with any aspect of the car - engine or transmission.
Hear me now, believe me later. Bad engine grounds can cause many strange problems like this. They suddenly appear and then they go away. The trouble may be due to something else but checking the grounds would be one of the first things to look at in my book.