Rough idle

jsidik

jsidik

New member
So, i just finished my motor rebuild, and the only problem that wasn't fixed is that it will idle rough when I start it, or when I leave it idling after driving. It will run at 1000 rpm for a few seconds then jump to 1500 0r 2000, then jump back down to 1000, then back up. It will continue doing this until I drive again. I've read that blow off valves can make it do this, but it started probably a year after I installed mine. Could it be my MAF sensor or my o2 sensor. Also I have a full catless exhaust system now, with no tune until next week or so.
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any help would be great. thanks guys.

 
Awesome, thanks!

-----Added 10/28/2009 at 04:40:42-----

Should I wait on driving it until said tune? Will it do any damage? Also, I've had the engine out for about a month, should i wait for the computer to remember a little before I do the tune?

 
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I don't know what the computer has to "remember." The memory will probably be wiped after sitting without power for a while.

I know that the ECU in Nissan Muranos with the CVT will actually adjust throttle response based on driving habits. Is this the sort of "remembering" you're talking about?

I don't know how healthy it is to drive it without a tune. I assume it won't blow up though.

 
I've got the boost control solenoid unplugged, so it won't overboost. I think it should last a week.

 
Did you change the intake?

-----Added 10/28/2009 at 05:56:28-----

It could be a vacuum leak a bad maf or a bad o2. Or it could be tuning related due to changing an intake or intercooler. What other stuff did you change since the last time it ran?

 
Wait a week and the tune will fix it.
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[rant]

Do you know this for sure? It sounds like you do, but somehow I doubt that you actually do. Not trying to be a jerk, but when giving advice, I wouldn't sound so sure of yourself unless you are in fact sure. It could be the tune, but how long after the exhaust was put on did this start? We don't know ...

What if him waiting a week for the tune blew the motor due to it being something else? All I'm saying is be careful what advice you give ... you're new to this whole Subaru thing. Sit back, read a lot, learn as much as you can ... even then I would only give possible advice. I'd hate for someone to try to hold you responsible for damage to their vehicle.

I've had quite a few years of experience, but even still I don't like giving advice. I'll tell people what I did, or how I fixed my problem ... but other than that, unless you know first hand, you're always at risk of being wrong. Hell you can even be wrong if you do have the first hand knowledge.

Just be careful.

[/rant]

And to help you out, I agree with Nate in that it sounds like some sort of vacuum leak ... the K&N I don't think would have affected anything tune wise. What vehicle is this in and how many miles on it?

 
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I was honestly thinking about this when I posted this specific post. Thanks for the advice though.
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No problem man, just trying to look out for you. I remember when I joined STM and I was in almost the same boat you are. I wanted to be able to jump in and join in more but I just knew that I wasn't really sure about a lot of the things being asked ... so I just waited to see what everyone else said and what actually solved the problem.

Some of my questions were even out of the gurus' leagues. When it came to my motor swap, there were few who were able to help ... but that's another story
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It's an 02 wrx. It started happening after i removed the cat in my downpipe but still had the 3 cat's in my manifold/up pipe. I've since used wire ties to seal all the vacuum lines when I did y build.

 
Have you tried cleaning the MAF?

How about resetting the ECU?

What exactly is this 'build' that you did?

 
I've cleaned the MAF, and the battery was out for about a month while I was building my motor. I didn't do many serous internal mods. Just rod bearings, rings, and head gaskets. I have a full catless system now though, and I'm thinking that is the culprit.

 
Just tuned, and the problem is still here. erratic varying idle, and violent jurking (hickuping) during low RPM's in 1st and 2nd gear. I just tuned it tonight, and havn't driven it much with the tune, so hopefully it'll learn more with the tune and solve the problems. If I need to be corrected, please do so. thanks

 
My problem still isn't gone. I've cleaned the idle air control valve, and adjusted the throttle cables. nothing works. When logging my car the throttle opening is 0% at idle, and it is still high. Also the throttle plate does not move when the rpm's jump. I could just turn the rpm's down in ecuexplorer, but as I havn't used the program much at all, I don't think I will. It would also seem like just a way to cover up a bigger problem. I'm pretty well stumped..
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Just a thought, but with your OBD2 tool, can you view live data? such as ignition timing.

Ignition timing is supposed to stay at a fixed number during idle to avoid the idle jumping around. Perhaps the computer doesn't "know" it is supposed to be idling and fixing the ignition timing?

Dunno what would cause that though, TPS not going to 0% when the throttle is closed maybe?

 
I've been trying to use ecuexplorer to read the cel codes, but i can't get it to connect. could this be because xpt uses a lock on their maps so you can't read them? I'll look into the ignition timing tps. thanks for the input.

 
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