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Old 12-27-2011, 02:01 AM   #1
nomorepoison
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Default Terrible bucking; at a loss

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??
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Old 12-27-2011, 05:23 PM   #2
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I don't have the diagrams to look at, but don't those sensors share a common power or ground? You can use a multi-meter to check power or ground at those sensors.

I had a similar issue many years back, the solution was either a power or ground wire, yours may be different, but worth a shot.

Thanks,
Rick
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Old 12-28-2011, 03:40 AM   #3
nomorepoison
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Im not sure if they do or not, but I will look into it.
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Old 12-28-2011, 01:24 PM   #4
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check hose to FPR
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Old 12-28-2011, 03:24 PM   #5
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sounds like a ground to me.
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Old 12-28-2011, 05:43 PM   #6
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I have this same problem. Except I have an early ej20g, code 45. The one thing I found between terminals 1 and 2 for the pressure sensor I get 4.65v instead of the 5v like the book says. Is the sensor grounded through the ecu? If I do on ohm test on that wiring it's a couple K ohm
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Old 12-28-2011, 09:49 PM   #7
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Quote:
Originally Posted by Jaxx View Post
check hose to FPR
Ya know, Im beginning to think maybe this might be part of it. Every once in a while I will get a strong wiff of fuel. Which hose? Just the vacuum line?
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Old 12-29-2011, 10:34 AM   #8
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yes the the plastic gets hard and cracks .. be sure to get a hose that fits well as it will see boost pressure
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Old 12-29-2011, 02:53 PM   #9
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I've replaced almost all of my vacuum hoses with silicon hoses and then to make absolutely sure I have perfect seals I use a zipties the like clamps to give an extra bit of traction on the vacuum seal.
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Old 01-08-2012, 09:43 PM   #10
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I'm thinking TPS.

When I was getting my car e-tuned, the throttle position was initially incredibly sensitive and I could barely drive it normally due to major bucking. Once the sensitivity was dialed down the issue went away.

Not sure how you go about troubleshooting a TPS
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Old 01-09-2012, 03:54 AM   #11
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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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Old 01-10-2012, 05:02 PM   #12
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On these older cars it's pretty much guaranteed to be an electrical fault if there is a code for one of the sensors. Which means mechanical things like fuel pressure, compression, or loose vacuum lines are not causing the CEL. As a few people have stated already, the ECU ground wires are one thing all of those codes would have in common.
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Old 01-10-2012, 06:01 PM   #13
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Would that be something that would just pop up suddenly? And would it make sense for it to pretty much only happen after I drive the car for a bit?

If that is the case, how in the heck do I go about fixing such an issue?
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Old 01-11-2012, 02:04 PM   #14
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Assuming that nothing mechanical is wrong. Crappy idle could be the result of a faulty coolant temp sensor,dirty MAF sensor, IACV, underperforming FPR, spark plugs, dirty injectors.

I would find out what the code is for your CEL first. The ECU will have the codes stored in reverse order newest first. You need to know what the ecu thinks the problem is. 96 and newer cars should have the standard OBD2 port. You get the code read. Usually the tool will even tell you what the code is. Then you replace whatever sensor it tells you is screwing up. That's it.

Find CEL. Fix issue.

If its the IACV that the ECU is complaining about, you can bandaid the issue by preloading the tension slightly on the throttle cable on non-drive by wire throttlebodies so the IACV doesnt have to work so hard. A byproduct of this is better throttle response . Use EVOscan or a scantool to make sure you arent monkeying things up by changing heavily changing idle throttle position.

You only want to add less than 1 degree to the butterfly valve in the throttle body. The IACV still needs to control your idle. You just want to make the IACV solenoid work less hard.
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Old 01-11-2012, 04:55 PM   #15
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I actually have pulled the CEL codes, they are as follows: 31, 45, 23, 24.
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Old 01-12-2012, 03:21 AM   #16
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Quote:
Originally Posted by nomorepoison View Post
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.
Pertinent details from original post: MAF, TPS and IACV. Most likely issue: IACV. Try preloading the tension on your throttle cable and reset the ecu. Worst case try your luck at cleaning the IACV. What are you using to scan codes? EVOscan or something else? Does your scantool give you any reading at all for the throttle position from the TPS? After reseting the ECU: Log the readings from the TPS and IACV.

I do not know if the 98 ej20k ecu is the same style as the my94 but IIRC the ECU reset procedure recalibrates the readings for the TPS. I'll have to hunt around and try to remember where I read that.
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Old 01-17-2012, 03:32 AM   #17
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Im just counting the light blinking. Im over here in Japan and dont really have a way to get ahold of scanners, at least not easily.
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Old 01-17-2012, 12:00 PM   #18
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Quote:
Originally Posted by nomorepoison View Post
I actually have pulled the CEL codes, they are as follows: 31, 45, 23, 24.
I looked at those code numbers on my cheat sheet.

23 is Air Flow Meter (I think MAF)
24 is Air control valve (I think IACV)
31 is Throttle Position sensor
45 is Pressure Duty soleniod (I think MAP sensor)


I'd clean the MAF and Clean the IACV. When you do an ecu reset if you do it correctly it should calibrate the TPS. So try it and see if the other codes go away.
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Old 01-20-2012, 03:21 AM   #19
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The maf is already known to be a non issue, pulled one from a running car, put it in, no difference.

Im resetting the ecu by pulling the hot side off the battery, and holding the brake down for 10 seconds or so, then putting it back together. Ive done this after just about every attempt to fix it, and all 4 codes come back.
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Old 01-20-2012, 08:08 AM   #20
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It takes more time than that to clear the ECU memory. Leave battery disconnected overnight (or for at least 30 minutes) or connect both black and green connectors and drive at low load till CEL is flashing at 0.5 second intervals.

I had a similar problem due to an intake leak. Car would work fine if ECU was reset. The car would work fine on initial startup as well. However as soon as I got to a stop light and waited for let's say 30 seconds at idle, the car would bog down as soon as I pressed the throttle. Releasing the throttle would return it to a perfect idle. After changing ECUs and MAFs (which didn't help), I found there was a small leak just after the MAF.

However the codes are another issue, in my case I didn't have any codes. First try fixing the codes and if the problem does not go away, look very carefully for an intake leak.
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Old 01-24-2012, 03:10 AM   #21
nomorepoison
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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.
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Old 01-26-2012, 04:16 AM   #22
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Big update here:

Replaced the TPS, IACV and ignition coil with known good working parts, absolutely NO change in the way the car ran, even after resetting the ecu.

Its starting to kind of backfire out the intake as well....

Maybe the fuel pump, or coolant temp sensor?
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Old 01-26-2012, 11:57 PM   #23
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I'm in pretty much the same boat here, sorta pulling my hair out. I'm gonna get a fuel pressure tester here soon and check that, I checked my ECT at the ecu and the resistance seems fine. I've replaced the cam, crank, maf, cleaned iac, and adjusted the tps. I sorta dream at night it is the fuel pump.
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Old 01-27-2012, 12:46 AM   #24
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Quote:
Originally Posted by nomorepoison
Big update here:

Replaced the TPS, IACV and ignition coil with known good working parts, absolutely NO change in the way the car ran, even after resetting the ecu.

Its starting to kind of backfire out the intake as well....

Maybe the fuel pump, or coolant temp sensor?
Backfire out the intake???wtheck That shouldnt be remotely possible with a turbo. I mean besides the physical restriction of the intercooler and turbo there is (provided the turbo spins freely) a steady amount of pressure from the turbo forcing air into the manifold.

Could your turbo be pooched?
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Old 01-27-2012, 02:22 AM   #25
nomorepoison
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No, shouldnt be, it was doing this with the td04 that was on there, and when I put the inlet on I put on a spare vf22 I had, same issue, so it seems unlikely.
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