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Discussion Starter #1 (Edited)
Guys, I've talked to several people who are quite knowledgable about subarus and no one can work out what could be ailing my 2k4 Sti. Here are the details:

After a very nasty storm here in NJ (6 inches of rain) the car will start but idles VERY rough after 10 seconds of being started. The rpm's will surge then fall below idle then surge again which will then repeat over and over. The afr's, as read from my wideband 02 shoot from 12-15 to 12 and back up again in tune with the rpm surge. Before the 10 second point it idles dead balls perfect which leads me to believe it's a sensor failure as the cold start mechanism should disable the sensors until this point.

First thing I did was see if it was throwing any codes by use of a deltadash but it was not. I then tried a new maf sensor from a 2k2 wrx which the part number matched identically yet with the same exact results. At this point I removed the utec but same results. Next I unplugged the map sensor and tried starting. I do not have one available to me to test with so unpluggin it was all I could do. This seemed to keep the idle much more steady for 30 seconds or more but began to stall soon after. At this point, I am ready to either buy a new map sensor and try my luck or take the car back to stock and have subaru look at it which I do not really want to do for obvious reasons.

Mods are turboxs shortram, turboxs utec, joe p or similar mbc, turboxs tuner and turboxs stealthback exaust w/ cat. I was running the shipped stage2 map with great results minus the documented stumble at the crossover point which I hadn't gotten a chance to tune out.

There was no visible water in the engine bay when this first began the day after this storm and we had no flooding although the rain was torrential and I was assume angled at times. Any help would be greatly appreciated so I do not have to stock the car and take it back to suby. The situation is so odd because the car ran just fine the night before the storm when I parked it.

-Seneca
 

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is there any way water could have been pulled into the intake?

drive through any REAL deep puddles?

with a short-ram, i'm not sure how that could happen, but it's the only correllation b/w rain and major problems i can think of.
 

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Is it possible to run the ecu codes?
This should tell you if a sensor has failed. I think your right about a sensor as it runs correct at startup.
 

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dark_rex said:
is there any way water could have been pulled into the intake?

drive through any REAL deep puddles?

with a short-ram, i'm not sure how that could happen, but it's the only correllation b/w rain and major problems i can think of.

yeah that's what i was thinking when i was reading the thread..than he said short ram..i dont know how that's possible


off topic: ..dark rex i like your sig....btw i'm armenian haha...so how come you and eli were talking about armenians??
 

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Discussion Starter #5
The car ran fine the night before the storm and was showing these signs the day after when I went out to start it so no thats not possible. I WAS worried about the maf possibly failing due to the oil in the K+N but I've ruled that out with a new maf sensor. I also had a friend come by w/ a deltadash and the car throws no codes whatsoever. I've added this info to the original post. =\
 

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Need to run compression test..
To me it sounds like bent/warped valves. Were you driving the car hard the day before? That would explain the fluxuating a/f ratios. Blown headgasket(s) might not be out of the question either.

Could be a fowl plug, pull the dipstick and smell for gas. If you have a fowl plug the unburned gas will go past the piston rings and get in the oil.

I can't see any corelation between rain and the problems your having.

If compression is ok, and the oil smells fine, it could be an ECU malfunction due to the piggyback setup you've been running. A reflash to the ecu might fix it, or at least show what codes SHOULD be thrown being the engine isn't normally running. After a compression test and plug test I would take it to Subaru.
 

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Discussion Starter #7
I wasnt driving it any harder than I drive it normally and it was purring like a kitten when I parked it. Im not sold on the rain 100 percent either but Im not ready to do a compression test yet either. The fact that it idles perfectly for 10 seconds would not be the case w/ a blown headgasket would you think? As for codes the only one its thrown is map sensor error when I unplugged it in said test. As for the utec, a reset of the ecu would cure anything a "piggy back" could do to it.
 

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Take out the utec and mbc. If it still has the problem drive it to the dealer, if they care about a turbo back and an intake before looking at a problem you probably want to find a new dealer.

Also make sure your maf is installed facing the right way. Does it keep running if you give it gas?
 

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map sensor is the problem. scan at idle then at ign, on, but motor off. look at map voltage. Are you running a fuel cut defender?
Borrow a map from friend.
 

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Discussion Starter #10
As stated above, the utec has been removed however the car is not drivable in this state. If I did not have to flatbed it I wouldnt be posting this right now and it would already be at my dealer. As for the map sensor, I agree it is the most probable failuree point due to water while the car was not in motion as it site just lower than the top mount. Can anyone confirm whether a wrx map sensor can be used in an sti just to test. I have confirmed they are different part numbers but with the sti only running 1 more pound of boost from the factory I cant see the specs being too far off.
 

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dark_rex said:
is there any way water could have been pulled into the intake?

drive through any REAL deep puddles?

with a short-ram, i'm not sure how that could happen, but it's the only correllation b/w rain and major problems i can think of.
Just like dark rex and awd said..u most likely got water in ur intake. Im from new jersey to and..that storm was BAD!!!!
 

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Discussion Starter #12
It was parked for the whole storm. So unless it came in through the scoop or the intake I doubt it but thanks for the suggestion.
 

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please do a follow up and let us know what it was. map sensor is my bet. Use a scanning tool, not utec. many auto parts stores have them to use for free!
 

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Discussion Starter #15
I used a deltadash to look for codes. It throws none. Someone suggested letting it idle for 5 minutes to see if it throws one which I will try and report back results.
 

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Have you tried just adding a bottle of heet to the gas tank? When I lived in Michigan, a couple of rainstorms were strong enough to get water into the gas (whether by humidity or backwards through the vent, I don't know). A couple of bottles of heet later everything was hunky dory.
 

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Discussion Starter #17
I thought it was possible I got some bad gas or got some water contamination but wouldn't you think it would idle roughly all the time not just after the 10 second initialization?
 

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Water and gas don't mix very well, so it usually has like bubbles of water in the gas. You will get a couple, then gas, then a couple more. Plus, when you first start, the car is on choke which runs rich, so water isn't as noticeable. Try it. It's much cheaper than some of the other options being proposed.
 

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don't need to spend a dime. Use your brain, and a scanning tool. Don't just guess and start throwing parts or chemicals at it. There is a very small chance that water is in the gas, unless you left cap off. It is a sensor problem!
 
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