low idle problems

[mesoslow6969]

Hello everyone. I just bought a 1994 legacy wagon (turbo awd model) a week ago.

There was an oil leak coming from the valve covers, and also i didnt know if anything had been taken care of before i bought the car.

Before doing the tune up, I had a low idle (rpms dropped under 500).

When i replaced the valve cover gaskets, i noticed there was oil on the spark plugs. So from that point i decided to do a tune up.

I replaced the valve cover gaskets/bolt washers, air filter, oil change, new gasket/o-ring for the filler neck tube, spark plugs/wires, pcv valve, fuel filter, and battery.

The car no longer leaks oil and runs pretty good. The next day i was driving and came to a stop light and all of a sudden it started having the low idle again. This time the idle is actually a little bit worse.

As soon as i stop for a longer period of time, it drops under 500 rpms and a "knocking" sound or maybe more of the engine sounding like its about to die and it goes back up to 500 and it fluctuates. The car hasn't died... yet. But the low idle and the engine struggling when at a complete stop is worrying me.

I was looking at the threads and alot of people are talking about the IAC. If it is the IAC where is it located on the turbo models? I saw the video on youtube, but the spot that its in is where the "chimney" is for the turbo. or at least i think thats where its located. I'm not very good at troubleshooting, so any advice would be appreciated. thanks.

[N1446]

The IAC is on the passenger side of throttle body, slightly below the intake manifold. On the intake there is a larger"1inch?" tube running off the cold-air intake ducting -into the IAC face, right after the MAF sensor. Three bolts holding it to the intake manifold and 3 tubes are attached to it. 2 smaller have coolant in them and run into the intake manifold, 1 larger is for idle-air passage from the intake ducting.

To remove the IAC and 3 pieces of tube total, you need vice grips/ needle pliers to remove the stays, and if you do remove the IAC you should have a new gasket to mate it to the manifold properly after cleaning. If not, the coolant passages are shared between it and the manifold and when a poor seal exists, white smoke will pour out the exhaust from the coolant entering the intake manifold..

is the check-engine light on ?

[mesoslow6969]

no check engine light is on... if it isnt on, do you think it might be something else other than the iac?

[N1446]

You want to do this. This is the best thing about your car., if no check engine light is on, go for a drive in d-check mode.
After 1 minute of driving, the check engine light/CEL will flash you the codes in morse code and identify a problem-s

Its best to do this with someone in the car to read the CEL's morse code for you, so you can watch the road.

-

One thing to note is that when you turn the ignition to "on" in d-check mode, the relays and fans will turn on then off repeatedly. this is normal.

Your check engine light comes on when the fans turn on, then goes out when they shut off. If your engine light does not turn on when the fans do then your check engine light is faulty.. and you may have codes and not know.

Josh \Legacy777 has all you need posted on his site for diagnostic trouble shooting and code reading 1st gen legacys.

http://www.surrealmirage.com/subaru/engine.html

As for other problems, poor vaccume is always suspect especially in colder temperatures as the hoses are brittle and tend to crack break easily.

Welcome to the site.

[mesoslow6969]

thanks so much for the help and advice. I will try to get this checked out as soon as it clears up a little outside. I'm in Chicago so its snowing pretty good errr.. bad depends how much you like snow. lol. i'll keep you posted.

[lucas]

hey man welcome... just a thought i just changed my coolant temp sensor and helped with poor idle some. Lucky for us these old cars are full of surprises haha

[mesoslow6969]

cool, i'll look into that too. thanks for the advice and warm welcome. Truthfully i dont know how much money i want to put into the engine right now. I'm debating on doing an sti motor/trans swap. I still have to do my homework and see if it is a better idea to build this motor into a quick grocery getter. we'll see when it starts to warm up. lol

[92.Legacy.SS]

i think were having the same problem... today i filled my car up with premium (normally i put plus in i know bad part on me..) but after getting to school car ran fine then went to get lunch and sat in the parking lot with car running and it would almost die it would bounce from normal idle to super low and i'm not sure what is the problem im new to legacys but the car ran fine before even at idle.. could it be the fuel pump or filter?

[mesoslow6969]

i'm not sure about the fuel pump, but when i did the tune up, i replaced the plugs, wires, battery, fuel filter, valve cover gaskets, pcv, and i just replaced the coolant sensor... its still idling rough.
Next I got to clean the IAC valve and see if it is dirty. Legacy777 recommended sea foam, and another member talked about taking rubbing alcohol and q-tips and gently swipe the IAC.
Another wierd thing going on with my car is that the rpm needle will twitch alot during idle. I can't tell if its the idling problem, or if my motor mounts are so bad that it's causing the car to shake enough to cause the needle to twitch.
Worse case scenario i'm going to dish out the 400 bucks for a new IAC... I hope it won't come to that though.

[jefferson]

My car has had idling problems from day one and I think I fixed them tonight. It was a combination of things. I replaced my iac with a new one and got no improvement. Big bummer. I had cleaned it before with no improvement then either.
My problem was a high idle most times. After replacing the iac there were times the car idled very rough and threw a code 24 which is the iac. I couldn't understand how a brand new iac would throw a code. I got my answer in a post by kenwedpo in a starting issue thread. It mentioned a rough idle and code 24. The solution was to replace the ignition relay with a new updated part number. It helped my car. but still wasn't right.
Turns out my diaphragm was blown in the bypass valve which was a vacuum leak. Now I really didn't have a high idle problem, but a too low and rough idle, but no codes. Tonight I put in my low mileage ND plugs I saved when I put in the E3 plugs as an experiment. I wouldn't have tried them except Horsepower tv reported horsepower increases and better fuel consumption after a dyno run with those plugs. I noticed neither and I log every tank of fuel and list all changes I have made to the car.
I feel like I have a brand new car compared to the way the car drove before. The car pulls harder, runs smoother and idles like it should have all along. All my driveability issues have dissapeared with the new plugs. I am really anxious to see how my mileage does now.

Sorry this is so long and I hope someone gets some useful info out of this. I am just jumping for joy about how my car drives now and had to tell someone.

By the way, what spark plugs did you put in your car? I think NGK are the recommended brand, but I like ND and have used them for years. I don't know if I would use any other brands. Another thought is how good of wires did you put on. My son bought a set of O'reilly wires and was having issues with the idle on his car. He took it to one of the Honda guru's in town and when he pulled up and got out of his car the guy heard it running and without my son saying anything told him he needed some new plug wires on his car. My son told him they were new. He then proceeded to tell him not to get the cheap wires, but to get the better more expensive wires and with that his problem was taken care of.

Jeff

[lucas]

interesting ^^^^ never thought of that. thanks man.

[Legacy777]

Jeff,

Good info, and thanks for sharing.

I tried all sorts of the different plugs for these cars back in the mid 90's. They like regular copper NGK plugs the best. I tried all the different bosch stuff. I also tried some fancy 3 prong NGK electrodes plugs. ND and NGK are probably pretty comparable. I think NGK is more readily available, which is why they are more commonly recommended.

Regarding the plug wires, yes, get a good set of plug wires. They can be had online for cheaper than what you can get them for at the autoparts store. I got a good set of NGK 8mm plug wires at www.sparkplugs.com for around $53. They'd likely be a bit more at the autoparts store.

[mesoslow6969]

today i actually trying cleaning the iac wit the alcohol, and qtips... but its an almost impossible task.. at least for me it was.

at first i thought all i had to do was unsrew the two tiny screws and then clean it... i didnt realize that its just a "solenoid." well i cleaned it anyways. when i tried looking down to see if i could get to the 2 bolts and the coolant line, i was like eff this. put the intake back together, put all the hoses back together. i started the car and it was in limp modes from having the battery disconnected.

it sounded normal. next i revved it a little and once i let go of the throttle cable it idled soooo bad like it was hovering on the 0... i got scared turned off the car and rechecked all the hoses, made sure all the plugs where plugged back in, and double checked the spark plug wires.

I turned the car back on and it was idling at 500rpms (which was better than before i even started this task). I let it run for 15 min and took it around the block and it drove normal.. way better than before.

when i was driving home, i floored it on the highway to test out the new motor mounts i just put in, and when i got off the highway it was idling just fine when i came to complete stop.

Now i was backing into my garage and the rpms dropped drastically once i put it into reverse. I got worried so once i got it in the garage i let it sit for ten minutes while waiting for it to "cool down" since i floored it on the highway. Turned off the car and turned it back on. It idled at 500 rpms again.

So either i fixed the problem even though i half assed it or i got really lucky. Sorry for the long post... i'm kind of too detailed when it comes to explanations. lol.