1993 Suburu Legacy EJ22E H4/IDLE ISSUES

So I have an 93 legacy with 100k miles on it. And I am currently having issues with idle surging. Now I originally started out with testing the alternator. It came back saying that it has ripple issues. So I decided to change the alternator and the alt belt as well as the spark plugs, spark plug wires. I thought all of this would fix my idle surging issues. Well it didn’t at all. The car doesn’t seem to surge while driving its only when I come to a stop and I’m in drive with the brake pedal compressed. Also it seems to get worse when I am running the headlights. I disconnected the positive cable on the battery while the car was running and it stayed running. Not sure what to try from here? I know that the Y-pipe and cat has a bunch of holes in them and it is leaking exhaust bad not sure if that has something to do with it.

This can cause all sorts of electrical damage to your car, such as popping the computers, as the 12 volt rail surges to 40 volts or more. And what did that prove? that you electrical system can survive (we hope) high voltage surges?

Isn’t that a tell tale sign that in the event of doing this that the alternator is not the issue?

The surging idle might be caused by a hunting Idle Air Control valve.


The IAC valve controls the engines idle speed whenever stopped with the brake applied.

Sometimes these valves fail where they hunt for the proper position for the idle condition, and the idle surges.

Here’s a word of advice.

Never disconnect the battery while the engine is running.

Doing so can cause a voltage spike destroying computers and modules.



Isn’t what a sign? that the car survived without electronic damage? that is only a sign that the processors are well protected.

thank you I will try cleaning and/or replacement of the IACV.

interesting Bill but honestly nothing you have said so far has helped solve, or be productive to my original question. You can contradict what has already been done. But that isn’t a solution to my issue that is just a possible side effect. But thanks for wasting my time!!!

Wasting your time ? Being told that one should not disconnect a battery while vehicle is running is not wasting time. Besides , this is a forum so you cannot expect every reply to be to your liking.

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How is it not a waste of time? You are posting possibilities about things that aren’t even asked? So yes thanks for wasting my time. It isn’t about liking at all ether it’s about finding solutions for people’s issues. My issue isn’t that I disconnected my positive battery cable while car was running. So please waste somebody else’s time with your ignorance. And learn to read and respond to actual questions like we learned to in the first grade!

Not to mention a distraction from the real post. If you want to discuss the severity of disconnecting a battery while car is running then create another post.

It is not @BillRussell 's ignorance, but yours @Lucifer28.

He was only trying to educate you on the issue of disconnecting the battery cable to test the alternator/or charging system.
This was an old method done on cars pre 1980s…maybe earlier. This method still…though wrong…is still being recommended by people that have continued with this myth.
With the new electronics it can do all sorts of damage.



I think the OP is being way too harsh and sarcastic. I’ve got a theory but I’m not going to say a thing…


Exhaust leaks can cause this. It confuses the computer’s calculation for the air fuel mixture. The computer presumes the engine is air tight. If cleaning the idle air control doesn’t fix it, repairing the exhaust system is probably the next step. It has to be repaired anyway, right? Brain cells are more important than the cost to fix the exhaust. Intake air leaks (such as vacuum leaks) are another possibility for surging.

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I think damaged brain cells from the exhaust leaks have made the OP irrational and cranky. Reading his posts is therefore a waste of time.


Here’s a tip, don’t get upset and tell other posters here who have more mechanical knowledge than you about wasting Your time when all they are trying to do is help you understand some things about your car. Which by the way, they are taking up their valuable time to post here to explain to you in a kind matter.

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Upset about posters distracting the topic on some theories and so called knowledge that is false in this situation. And continuing to arguing something that pertains to nothing about my original question? This site is here to help. What’s the point of it if a person is continuing to not help at all?

I think people with mechanical knowledge like yourself I’m guessing has wasted your time posting this instead of being helpful and reading the question and answering it. Apparently the ability to comprehend is really hard on this site.

I would like cdaquila to determine whether the OP’s comments regarding other forum members are appropriate.

Right but I did not recommended it and don’t you think the first time was enough? My point to the waste of time is people deterring other people from this forum because they’re posting things that don’t pertain to the actual issue. Think about it he read my post and then chose to pick something out and criticize it over and over. Where is the other mechanical advise? Anybody can research this and read the 50/50 decision on this method.

I would like this too because if people can come and look for help on this forum and members are allowed to continue to post things that don’t pertain to the post just because they’re drunk at home and don’t like something. And then continue to be counter productive on the situation just like yourself then what’s the point of this forum? Really? Admin somebody tell me how you can allow members to deter people from getting help on here? I see it all over! Not one person that has came to bill russells aid has offered any sort of help regarding the situation. This is a forum for helping others is it not?