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2000 STi Limited Wagon
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67 Posts
Discussion Starter · #1 ·
Alright everyone, I seriously have no idea where to go from here.

Randomly while cruising one day my car lost all power when on throttle. It idled fine, but as soon as I pressed the pedal, it completely bogged. Pulled over, checked everything, and tried to drive again. At this point, it woudl drive but buck wildly at every pedal position save for WOT and idle.

I found a hole in my inlet pipe, so thats been replaced, but didnt solve the problem.

Im getting 4 check engine lights, TPS, MAF, IACV and pressure solenoid. I replaced the MAF and the solenoid with zero results.

Ive also checked the car for boost leaks and found nothing, at least nothing major. This would bother me more, but the issue is constant, on and off boost.

Car is a 98 STI GF8 with an ej20k. Any ideas??

SMALL UPDATE:

Was running an ssqv to atmosphere (got it for free) and thought maybe that was it. Put on my stocker, and had the exact same issue, no difference.

The car seems to run totally fine first thing in the morning. Drove 25 minutes to work without a single issue. Got in it at lunch today, drove like crap.

Seems like when I have a CEL, as soon as I tap the throttle it goes away. As soon as Im off throttle and it returns to idle, it comes back.

Also, idle is garbage. All over the place. Vacuum is sitting around 500hg or so.

Checked the vacuum lines to the fpr, and pretty much everywhere else. They are all supple and nice. I do have my boost gauge sensor attached to a T off of the fpr though. But its been like that for ages.
 

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yep. you heard me.
‘18 E63s AMG wagon & 10 Subarus
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6,473 Posts
sounds bizarre. maybe you have a plugged injector.. or a bad knock sensor. or... hmm idk. I was going to suggest MAF at first but you said you replaced that.

did you reset your ECU after you fixed the inlet hole?
 

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2000 STi Limited Wagon
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67 Posts
Discussion Starter · #3 ·
Yes I did, and have done so again after just about everything else I have tried.

I was kind of thinking knock sensor too, but wouldnt that throw up a cel for knock already?

Another sympton has been pretty bad gas mileage.
 

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MY00 //// BRP 2.5RS coupe
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3,369 Posts
I know you said you checked for vacuum or boost leaks, but all the symptoms do still point to that.

And due to the cel maybe limp mode too?

Or not to scare you, maybe something happened while you were driving with the big inlet hose leak?

I would start again with,

Vacuum leak
Fuel
Spark
Sensors

Btw do your cel flash?
 

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2000 STi Limited Wagon
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67 Posts
Discussion Starter · #6 ·
Use starter fluid when checking vac leaks. Spray it around the lines and intake tract while idling, if the idle changes (either chokes or picks up) then that's your leak.
I tried this and cant seem to get it to do ANYTHING no matter where I spray, even so far as spraying straight into the intake mani via the brake booster line.

SOMETIMES the cel flashes, but usually it doesnt. The car is certainly going into limp mode though, anything the CEL is on, limp mode is too. I feel like I have gone over the car with a fine toothed comb a million times for vacuum leaks haha, but maybe that is waht it is. As far as the inlet pipe maybe being messed up, the car is having the same issue as before and it seems unlikely it would be messed up in the exact same way. Plus, I have checked it a whole bunch of times as well.
 

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RUSSIAN FOR HIRE
2000 Impreza RST
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2,425 Posts
i was a honda guy but first things always are vacuum, spark, fuel, and sensors like monster said above. similar thing happened to me when my distributer on my b20vtec started going out because i had a crack in the cap. and to my wifes car when she got water into the spark plug well. check your plugs and coils. also can be a wiring harness issue. if you did home made wire merge and left bare wires it could be grounding out somewhere and trippin your system out.
 

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MY00 //// BRP 2.5RS coupe
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3,369 Posts
If it is flashing it usually means misfire, you can also verify this with a obd code reader.

If it is check for spark

The stock inlet hose is notorious for cracks and leaks, including slipping off the turbo.

I am still leaning towards vacuum leak and causing sparkplugs to go bad. I would not drive on this anymore as your car may be running really rich or lean depending on the situation
 

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2000 STi Limited Wagon
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67 Posts
Discussion Starter · #10 ·
No home made wire merge. The cel does flash like I said, but it doesnt have a misfire cel. Any idea what kind of vacuum leak would come up ONLY when the car is warm? How can I check my grounds exactly? Never had a problem with them before.
 

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RUSSIAN FOR HIRE
2000 Impreza RST
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2,425 Posts
if the CEL is a misfire it sometimes dissapears and reappears and makes it hard to catch i had that for a while with my wifes car. felt like it had a piston misfire but wouldnt pop up. one day i jsut happened to be by a car shop just as the CEL turned on and sure enough PO301 piston misfire. just a heads up.
 

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Green 97 OBS
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1,840 Posts
Check the TPS voltage sweep via your ECU- it should start at .45-.55v and then evenly increase as you open the throttle. If there's a dead spot, the voltage will either stay at a certain point as you open it or it could even drop completely off.

If that checks out, I would say its probably your O2 sensor. Mine didn't throw CELs but still made the car run like crap. I used a scangauge to monitor the short term and long term fuel trims, which show the adjustments the ECU is making to the amount of injected fuel.
 

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00RS Coupe, 00RSwaggin
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454 Posts
front 02 sensor is a wideband 02 just to let you know, my car ran like fucking garbage and i had no idea why then i replaced front 02 sensor and the car is running once again like it used to. Althoght i never had a bucking feeling in my car it just ran rich/lean whichever it preferred at the time
 

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2000 STi Limited Wagon
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67 Posts
Discussion Starter · #20 ·
I tried to check the TPS via the ecu, but either the pinout I have is WAY off, or the tps is putting out around 10v. Checked it at the actual tps though, and Im only getting around .2 at closed, up to 1.2 at full open.

Also changed my intake mani gaskets, just to be sure.

Shouldnt be cracked ingition coils, as its just got a coil pack, not coil on plug.

AND, I only have the rear 02 sensor on this car.

Thanks everyone for all the help so far, at least I feel like I am maybe getting somewhere.
 
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