I have a 95 imoreza l 1.8l front wheel drive around 149k when my cars is cold it makes a knocking noise until it warms up, and my gas mikeage has went from 23-25 to around 18 the car has made the knocking noise since i got it (had for about 3 months) i replaced the plugs, wires, fuel filter, air filter, and oil 2 days after i got it so i dont think its any of that but i could be wrong any help would be nice

Does the knocking noise completely go away when it's warm, then it runs nice and smooth?

If so, probably what we call piston slap. Engines can have it for hundreds of thousands of miles, won't hurt anything.

My 2.5 does it so bad you'd think it's going to throw a rod any minute, then it quiets right down.

Gas mileage in the winter will go down on every car. They use a different gas in the winter (assuming you live somewhere cold). It's not as efficient, so you burn more of it. Letting the car warm up uses gas. Also, it takes the engine longer to come up to temperature, so it's not running as efficiently, burning more fuel.

 

What brand of plugs and wires did you use? Subarus aren't always happy unless you just use the cheap NGK plugs and the NGK wires.

 

Here's what happened when I tried to second guess making my car happy.

Wondered why it was running like crap about 4000 miles after replacing the plugs.

I know the 1.6 and 1.8 in europe are very prone to piston slap when cold. Maybe you can do a compression test? Or what might be as well is that the spark plug came loose. This could explain knocking as well.

(if running fine, did you change driving pattern, lots of city, maybe a sticking brake pad?)

 

 

What happened with the spark plug? did it got hit by the piston or just broke off? If so what make?

Edited February 26, 201214 yr by rverdoold

Bosch platinum. It was the same length as a stock spark plug. So there is no way it could have been hit by the piston, other than the plugs the engine was in really nice shape with about 95k miles on it.

Changed to NGKs, and never had an issue afterwards.

 

Three of the for looked like that, one was just severely worn. No idea why it happened. But I drove it on the NGKs for about 30k till I sold it without one issue.

Its runs perfectly fine when its warm and i know there ngk plugs and im sure its the cheap ones and i dont have ngk wires idk what brand they are

 

I do live somehwere cold and i dont believe ive changed ive always drove this way, so i dont think its that, as far as gas should i run higher octane? Ive read people gettin 30+ and im not getting 20 lol i do alot of on and off ramps on the highway mayb the constant push to get up to speed is whats doing it idk

You could try higher octane gas. Some people say they get so much better gas milage with the stuff that it's actually more economical.

 

I've tried it and gained a point, maybe two. But not enough to justify.

You've replaced a lot of stuff, have you checked to see if the O2 censor is responding quickly, or if it's tired?

 

I know it's not a legacy, but my GL did this. Gas mileage dropped significantly with no CEL codes. The O2 was just responding slowly when I checked it, by the time I got home from my trip to replace it, a code had been set. But it took about 2 months for that to happen.

Hmm idk ill check i think my cars obd1 since its 95 i havent cared to look, and i dont have a scanner for obd 1 so yea and gas is goin up if the higher octane ismt goin to do much i dont really care to waste the extra money i was goin broke with my nissan cuz it required it

Well, GL isn't OBD-anything. So I wasn't using a scanner. I was using an oscilloscope right off the sensor.

 

But I understand that not everybody just has an oscilloscope just chilling under their desk....

Edited February 27, 201214 yr by 987687

Haha ive never even heard of one of those i rememberanoter problem i have, when i frst drive the car the transmission shifts really hard into gears, but after i drive it a little it stops.

im guessing it warms up slower then the engine because it isnt doin much when im just idling, but i still feel it shouldnt do it.

18 mpg with a fwd 1.8? You definitely have a problem. It isn't the on off ramps doing it. I have the same setup and have never been below 25 mpg.

 

Check all your vaccum lines, clean the MAF and throttle body(use the cleaners made for it).

 

Does the CEL come on when you start the car? It may have been disabled.

 

What is the mix of ethanol in the gas you have been buying? Try other gas stations as well, find the newest one and try the first.

 

Your hard shifting is exactly what you think it is. Thats just how the transmission is.

I put 87 in it, i dont know anything more than that. no cel at all brake light turns on cuz i need new breaks and the fluid is low cuz of it, how do i re enable the cel if it was disabled? I got it from an older couple so i dont think theyd do it but never know, but i will check the vaccum lines and clean the maf and throttle body and see what that does

When you start the car the oil, CEL, battery and airbag lights should all come on with the switch for a moment and go out. The people you bought it from may not have but a shady mechanic could have disabled it.

Maybe a compression test. It shows basic damages to the combustion chamber as in burned exhaust valve.

You have changed the sparks, air & fuel filter which would indeed be the starting points. Maybe one of the cams is out of sync with the rest. Hence a compression test can show that.

I dont think the cam has jumped time or anything cuz it starts perfectly fine and when warm it drives fine, i do think it needs a new alternator though, the lights dim out and stuff cinstantly, i can barely help jump someones car, could that be an issue? Also does anyone know what the warm idle should be?

yes, bad alternators can cause all sorts of problems, including damageing your battery - and other things that you wouldnt think would be related.

Like what was said above, if it quiets down after its warmed up its probably piston slap and unless its extremely bad won't hurt anything. OBDII started around 96 ,so your is probably OBDI . On OBDI vehicles you can have a lot going on ( wrong ) and never get a code. Sounds like you need a tune up.

OBD2 didn't just start around 96, it was federally mandated in 96.

The 95 Legacy is OBD2, the 95 impreza isn't. At least, not the few I've worked on. Maybe a few late model ones crossed over.

 

OBD1 vehicles don't have as many stupid codes for things like emissions, but they will still throw codes when something goes wrong.

@ Robert Harick ive had the car for a little over 3 months and put new plugs, wires, fuel & air filters, and oil so im sure thats not the issue the only thing as far as tune up i should have to replace is the oil and im comin up on 3k miles soon.

 

Ok well ill look into a new alternator

 

Does a yone know the idle when the cars warmed up? I think mines low but im not sure

Are you asking what the idle should be?

 

Should idle at about 700rpms. The gauge might be reading low, I had a 96 leg that read low. Always thought I had a problem until I threw a scan gauge on it (obd2 on that car), it was right at 700.

So if it runs nice and smoothly without shaking, etc. at idle, it's probably fine.

Oo mine says its like 500-550, when the lights dim on the car it idles up and drops back down and sometimes it shakes when im in drive and have the breaks applied at a stop light

Oo mine says its like 500-550, when the lights dim on the car it idles up and drops back down and sometimes it shakes when im in drive and have the breaks applied at a stop light

 

500-550 when in neutral or in drive?

In drive the RPMs will be slightly lower. Lots of 4cyl automatic cars shake at idle, it isn't really just a subaru thing.

 

But it's speculated on here than vibration at idle can be caused by harmonics being set up by aftermarket axles.

I have one in my car, sometimes it vibrates, sometimes it doesn't. Sometimes it worse than others, dunno.

 

I'd start by cleaning up the IACV (idle air control valve). If it gets gummed up the engine won't idle properly. Which can especially cause problems with an automatic.

Mine was stalling, or near stalling when I came to a stop. It stopped doing it when I cleaned the IACV. Probably it wasn't reacting fast enough so the idle just dropped out and died before the valve could open up.

Um ill have to get back to you on the nuetral or drive thing cuz i dont remember, ik it droos but idk which one its at that idle, and idk if it has aftermarket axles but the previous owner gave me all the repair bills and i believe that was one of them, and if it did i bet thats what it is, cuz it only does it every now and again, and ill clean the iacv, i remember on my maxima i had to change that cuz it kept idling rough and stalling alot

The rpm in park is slightly above the line below the 1000 rpm line, it looks kind of high to be 500 so maybe thats where its supposed to be, idk

Being around that line sounds about right. Then it'll be a bit lower stopped in gear.

Yea when in drive its on the line or just under depending how long i drove it