i have a rough idle when vehicle comes to a stop..runs smooth when sitting in P and N..ive changed plugs,wires,filters etc etc..ive cleaned my iacv and the maf..ive checked for vacuum leaks..i also adjusted the idle up drove fine then parked car..came out an hour later and idle was right back to where it was before...any suggestions

Edited May 21, 201114 yr by andytheboot

Turned up the idle? hmm.

 

Do you have aftermarket axles?

There's been talk that they can set up a vibration at idle when in D.

it was only idleing at about 400 so i adjusted it to about 800..drove fine after that..i then parked for about an hour started the car back up and idle was back to 400...

 

axles are not aftermarket....

it was only idleing at about 400 so i adjusted it to about 800..drove fine after that..i then parked for about an hour started the car back up and idle was back to 400...

 

axles are not aftermarket....

 

You aren't really supposed to play with the trottle body linkage stop screw. Or tighten the cable, the IACV will correct up to about 4% opening anyway and make it idle right... Your idle is probably fine, your gauge just reads low. Lot of them do this.

 

If it's running rough at idle, the normal suspects. Plugs, wires, PCV, filters... blahhh. General tune up stuff.

98 obs 2.2 4eat w/ 125k miles

Mods - CAI with K&N cone air filter & DIY grounding kit

 

I too have a rough idle same as OP (vehicle comes to a stop..runs smooth when sitting in P and N)

 

Have - cleaned MAF, checked for vacuum leaks, cleaned PCV and adjusted idle (a while back haven't set back to oem yet)

Haven't changed plugs/wires or cleaned my iacv yet (need ngk platinum but recommendations on wires from autozone maybe?)

 

I pulled 2 IACV's from the local pick a part and they seem to move smooth after cleaning. will attempt installing one and cross fingers when i have time

 

noticed today i have a yeasty buildup in the PCV hose and other intake hoses and this worries me. installed my hoodvent cover plates in case it rains and was curious if seafoam would help to extract any additional moisture from my intake if there?

Did this 'rough idle' start after replacing any axles, or did you replace any axles recently?

 

Sometimes I think engine or transmission mounts can cause things like this too.

not really supposed to adjust idle on these cars its all computer controlled.

 

vibration in gear could be motor mount as well, but I have heard that most subarus have a fairly rough idle in gear compared to other cars. This is the experience I have had with all of mine but they are all higher mileage vehicles too.

How is the trans?

 

Fluid good level and clean?

 

Could be fighting a TC issue.

 

There may be a homebrew test for a TC test - I don't know.

i wouldnt worry about it.... i have a 95 legacy wagon with 2.2 l and it does the same thing.....its a subaru thing for sure.....i got used to it....

Yes, pretty common for the auto Transmission. I wish there was a simple fix. The only fix I now of is to sell the auto and get a 5sp :>)

Hm...if it is characteristic..... does anyone think it might have to do with the boxer style of the motor? Most 4 cyls dont 'box' the cylinders like the soob but include a counterbalance shaft. Maybe the way these cylinders box can cause a bit of vibration like that when under little load, such as stopped in drive?

My 99obw shook at idle after a good tune up. I noticed the 4eat trans mount looked off a little. I read other threads that say this engine design puts more stress on the trans mount then engine mounts. Sure enough, the rubber was all but gone from the mount Replaced it (70.oo ebay) and the idle smoothed out. Also seemed to shift better and smoother. prob just my imagination.

not my thread but thanks everyone

 

this is why i dig the USMB! people read and post timely answers/tips if not provide a direction in which to go

 

things i learned:

4eat's are stupider than i realized (well the TC at least)

i NEVER realized the first RPM line was 500 and NO ONE ANYWHERE has corrected me on this *facepalm*

Interesting… I searched for rough idle and in this thread some body mentioned if an axle had been replaced. After having the passenger side axle replaced I noticed the rough idle. Called the shop and mention what I read here but they had not heard of that. He said to bring it in tomorrow and they would check it out.

 

Why would having an axle replaced cause the idle to become rough? Is it because something was not tightened after the axle reacement?

 

Thanks in advance do any insight.

Because aftermarket axles have very loose tolerances that allow the axle housing to rock back and forth a bit with the vibration/power pulses from the engine. This causes a small vibration to turn into a large one because the axle sort of hammers on the inner joint.

One way to test the axle is to let the car roll forward slowly, about 6-12" usually does the trick, with your foot still on the brake. The vibration will fade away once the axle is moved to a different position. It may then come back on its own without moving, or you may need to roll forward another few inches before the vibration returns.

 

Known cures are to replace the axle with a rebuilt Subaru OE axle, or quality new after market axle. I think EMPI is the only recommended aftermarket brand. This is a commonly covered topic so there should be plenty of info about which axles to use here on the board.

 

If your old axle only had a split boot, ask the shop to put new boots on it repack the CV joints and put it back on the car. If the axle was making noise (clicking) order a rebuilt one from FWE (only rebuilds Subaru axles) and send in the old Subaru axle for core credit.

aftermarket axles will not create a rough or low idle. they can, on auto trans cars , cause a vibration when sitting with the car in D and your foot on the brake.(at a stop light) the test is that it goes away when you shift it into N or P.

 

in fact, the axle does not CREATE the vibration, it simply transmits the normal engine vibration to the chassis. i assumed it was due to the joints being too tight, but i do not know. i would think too loose would be cause the axle to rattle in between the two fixed points at either end, but whatever....

Edited February 14, 201313 yr by johnceggleston

I had a rough idle and a cylinder misfire code on my '05 LGT. Unfortuntely it turned out to be a burnt valve. Hopefully yours is something else.

I had a couple of these vibrate after a single axle replacement, but when I replace them in pairs-no vibration.

 

My 2 cents

Thank you for the responses. I tried the above trick from @Fairtax4me sugested of moving forward with my foot on the brake about 12" or so and that did seem to help although it seems to come back after a while a few stop lights down the road. I tried this before I swung it by the shop that did the repairs and since it wasn't as pronounced as before it was hard to replicate for the mechanic. I did show him this thread and he checked out the axle and we both did not see it moving during the test. He also said that they had used the FWE axles.

You may have an egr line that is starting to block up. Specifically the small one that goes from the BPT to the manifold.

Check the niipple end on the bottom of the BPT also. It gets very hard with age and is easy to split.

Have you been getting low egr flow codes?

 

O.

I have not had any low egr flow codes. I was running around today and it still is idling rough at times but it will smooth out in neutral or park. The mechanic said when it does idle rough to see if the rpm's come down at all... they do but it is barely noticeable,  maybe a needles width. What is the BPT? I have noticed that my gas millage has gone down a bit.

Also, my car is a 1997 Legacy GT with about 208,000 miles if that matters.

...... What is the BPT?.......

Back Pressure Transducer part # 6 in diagram.

I'd check it anyway. Check the operation of the egr valve itself.

As the tube clogs, flow is reduced and the egr valve doesn't operate like it should.

 

 

O.

Axles.

 

Replace them, if they are OEM...they are ready to be replaced after 15+ years.

Thanks for the advice everybody.

Did you check your crank pulley? If that is wobbling idle will be really hard.