legacycentral bbs

Hey guys, I’ve been dealing with trying to fix a really rough idle when my car is warm for quite some time now. Since it’s started, I’ve done plugs, wires, coolant temp sensor, coil pack, throttle body and IACV cleaning. When I cleaned the IACV the idle became almost perfect, however, when my fans kick on the idle becomes super rough again, then smooths out when they turn off. The car also almost stalls out if I turn it off then turn it back on again when it’s warm. Any ideas on what it could be?


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have you checked out your maf?

Not yet. That was gonna be one of the next things to check


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i would say with the fans effecting your idle like it does that it would be something electrical. since you havent checked your maf, id start there.

I finally got around to cleaning my maf and it made no difference to how the car ran. Still rough idle especially when the fans kick on. I’m kinda stumped since I’ve replaced or cleaned most electrical.


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Could be the IAC or the lead to the IAC. Also have you done anything with the grounds on the car? Most of the grounds in these cars are woefully inadequate. Adding an extra under dash to chassis, and engine to chassis will usually help with a lot of little weird things and make your dash and interior lights brighter.

I cleaned up my IAC a while ago and it helped a little, but not much. I tested my alternator and it was a bit low on the charging. I’m thinking that’s probably it at the moment so I’m gonna swap in a spare I have to see if that helps. I haven’t messed with my grounds at all, so if it comes to that, I’ll start throwing in more grounds.


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have you hooked up a voltmeter to your maf to see if its readings are within specs?

So I swapped a working maf sensor I got from a junkyard and it seemed to help a little bit, but it’s still running pretty rough. It’s not consistently rough or throwing any codes which is making it difficult to find the cause. Every time I start the car when it’s warm, the rpms drop like the car is about to stall, go up again, then fall again, then go back up to normal. If I rev the car right after it starts though, it smooths out without the fluctuations.


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I had similar issues and it was MAF related. I know you said you swapped out the MAF, but have you done any other diagnostic tests?

Also, what year and model is your Legacy? Do you have a MT or AT?

It’s an auto 91. Just for funsies, I swapped my stock air box out and put a pod filter on the car. When I did that, I looked down in the fender and saw quite a bit of mud built up in the intake. Maybe just not getting enough air? I haven’t had time yet to pull everything apart and clean it properly, but it seems to run a bit better with the pod filter

it still seems like an electrical/grounding issue.
for me, im a list person. i would (and have) make a list of all the issues im trying to diagnose, then i would figure out all the possible causes for each issue that i have. for each one i would then figure out how i could diagnose that specific cause to rule it out. another good thing to do is to figure out how much it would cost to either replace the part or test it, sometimes going from cheapest to most expensive is the only way.

thats just what works for me, if you think thats something that might help you, let me know and i can show you specifically what im talking about.

Kris, that would be much appreciated! I must admit, electrical is not my forte, so any help with electrical is always welcome


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There are so many things that can effect idle. It sounds like you're actually having more than one issue that's causing the symptoms. Hope you get them all nailed down, be sure to update us with any improvements you're able to make!

I seemed to stubble upon what was causing my issue. After months of running issues with no check engine light, mine finally came on with a knock sensor code. I pulled the old one out and found tons of cracks all though it. I’ve put over 500 miles on my new one and haven’t had any issues.


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