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FXT idles/cruises/boosts like doodoo sometimes

('06-'08) 
3K views 25 replies 5 participants last post by  DoubleJ 
#1 ·
Just got this FXT, 150K on it, and it has a couple small issues I need to iron out before I start making it pretty.

First one is an idle issue. When I'm sitting at idle, it idles fine, other than a strange diesel noise that seems to come from under the rear driver's seat. After I 86 the resonator (I hope it's a resonator, it's huge) I'll worry about that. If I stab the clutch with the revs up though, the idle will drop to almost stall, then skyrocket to near 2K, then settle to about 900, then back to the 700 I normally see. I pulled the beauty cover to find the IAC and clean it, and found no throttle cables, so I'm assuming no IAC either. Ideas?

Problem 2: When I've got the throttle just cracked, say downhill, but not engine braking, the car surges. Does it with my foot and with the cruise on, like I'm feeding a bit of throttle, then closing the plate, over and over again. Could this be related to the above issue?

Problem 3: Power under boost is pretty much never the same. Some days it pulls clean to redline, some days it seems to pull slow to redline, some days it just jerks lightly from about 3200 until it freaks me out and I shift. I've been short shifting to avoid it, which negates the purpose of having a turbo car. I have found that if I aggressively downshift, into boost, and hammer the throttle, it pretty much always seems to pull correctly. I checked the IC piping, seems to be in order, but other than that I'm clueless. 5000 feet, 91 Conoco is the best we've got here, new air filter in it. Can't find the fuel filter, in the tank maybe?

Sorry for the monster post with multiple questions, but I feel these all might be related. No CEL by the way.
 
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#4 ·
First off, you're right, it's drive-by-wire so you don't have an IACV.

Now, there are many things that could be the problem. Some of them off the top of my head:


We've got some good weather for the near term here in CO, so get to checking these out while it's nice out.
 
#6 ·
Haven't had a chance to work on it yet, but after getting back to town I took it for a drive and confirmed that if you roll into boost hard in 1st gear, it will pull through at least 4th so long as you don't drop below the powerband, with only a small stumble on the 1-2 shift. If you're doing 75 in 5th though, and just put your foot down, as soon as it comes into boost it'll pull a bit, then go flat for a bit, and repeat. I'll clean the MAF, check the connections at the battery, figure out what a boost solenoid is and report back. Plugs are brand new NGK something or others, and it feels completely different from a miss, more like the throttle body is being closed slightly.
 
#7 ·
While searching for what a boost solenoid is, I located a page where my symptom is described exactly, the cause of it being a dirty boost solenoid. Guess the wastegate just opens around 7PSI on it's spring, and the solenoid is all slow and won't bypass the boost signal properly. Hope that clears up some issues for me, I'll report back.
 
#10 ·
Well that repair backfired. I took the boost solenoid out, sprayed both ports with some carb cleaner, shook some black goop from the lower port. Also sprayed a bit in the tube to the MAF (pulled it off the MAF first) and some down the other tube after disconnecting it from the wastegate. I tried to turn the T down, but some still dribbled into my turbo. I started the car and let it warm up to operating temp, then idle for another 15 or so make sure any dribbled cleaner was out of the vanes before it could spool, then took it for a test drive. The surging issue is gone, and so is all my power. The car is still faster than my 2.5RS, but not by much. About an hour later, I threw a code, had it scanned and got a wastegate solenoid problem. I had unplugged it a couple times while it was running, so I'm guessing that threw the code. After four key cycles, it went away, but I've still got very little power. The surging at neutral throttle and crappy idle are unaffected.
 
#11 ·
This has been bugging me all night, so I went back out there and took it all apart again.
Question 1: Could the teaspoon or so of carb cleaner that got into the compressor housing have caused any problems? I didn't hear any funny noises from the turbo at any point, and all the research I did on the google seems to point to turbos spinning somewhere between 600 and 1000 RPM at idle. Located a couple posts where people had stuck a finger into an idling turbo and stopped the impeller, as well as a guy that said he could see the individual vanes as it spun. No hard facts though. It's bugging the crap out of me.
Question 2: How do you determine if the boost solenoid is faulty? Seems you'd have to be hard into boost before it even operated, then have some sort of gauge on the line from it. I'm pretty sure I can't buy a new one, slap it on, and return it if there's another problem.

That pill thing appears to be inline between the solenoid and the T. The T is crazy small, and I shook it and heard nothing, but there is a doodad about 2 inches upstream of it made out of metal. I ran more carb cleaner through the doodad, the T, and the solenoid. Pulled the T off this time to make sure none went into the spinny bits. I let the solenoid soak in it this time for about 10 minutes, then shook it out, let it dry, and misted the innards with PB blaster. That stuff fixes everything. Can't test drive it, kid is asleep, but I'm headed up for some skiing in the morning and I'll check back when I get home.
 
#13 ·
I took her up skiing today, no improvement on the way up, just couldn't seem to make any boost. On the way back down, as I got into Boulder, I needed to pull out into traffic to avoid some hippies, and I just about made a Forester/Civic centipede when I made what felt like full boost in 1st gear. Spent the next hour on the way home testing response in all gears, and it didn't seem to be surging or doing anything funny at all, just pulling a little at 3K, then a lot at 3500. It still seems to come into boost slowly if I just accelerate from 2K or so, but maybe that's just the nature of the car? I can also hear my BPV again, so the boost issue seems to be all good. Safe to assume that if it comes back it's probably time to replace the solenoid? If that's the case, is there any upgrade I should look into?
 
#14 ·
Drove a couple hundred miles today to see mom, and the surging is still occasionally cropping up in higher gears. 1 and 2 seem to pull fine, 3,4 and 5 are better than they were, but still not quite right. Should I do an OEM solenoid, or is there a better option?
 
#16 ·
I did the snorkus delete today, and while I had it apart I cleaned the MAF. The bulb had oil residue on the backside, and there was oil on the old filter when I tossed it a few weeks ago. The new filter is clean so far, and I cleaned the junk off the bulb. If anything, the idle issue got worse, there was no change in the neutral throttle surging, and I haven't had it out of town to check the boost surging, but I still think that's a solenoid issue.
 
#18 ·
I talked to a guy on Romraider, and he believes I'm getting a boost spike, which is why the MAF and WG lines are nutso. I do recall seeing a spike to about 15psi, and then a dip to about 8 when I had a boost gauge hooked up, so that seems to make sense.

Here's the weird part. It just got cold here in CO, very cold, and the surging issue has cleared up substantially. I can still feel the slightest bit of it in 4th and 5th, but it's gone in 3rd, and 2nd is also pulling much harder, almost ran into an errant mini van the other day when I got way more power than I'm used to.

Figure it's gotta be something with a temp sensor, or the MAF, or something I don't even know about, but around freezing and below, car seems to run much better. That would also explain why I didn't notice it on the test drive, bought the car in November.

Any other ideas on this one?
 
#21 · (Edited)
Need throttle position too to see what's going on.

My first reaction is though, do you have boost gauge on the car? What is causing the error... or can romraider just not read the boost?

If you have any data from the Maf that would be cool too. Basically timing, air/anything, fuel/anything and throttle position. I really don't know whats available to you on romraider.

Looking over your posts you say stuff like "snorkel delete" and "oil on the bulb" which makes me think you may have some modifications that could be causing issues too.
While for snorkel delete makes me think you removed a snorkel most people put on for fording water I have no idea what "oil on the bulb" means.

And you have just kept driving this car like this for a year?
What codes do you have? If the car is doing all you say (which I believe) you will have some codes. Also, for a the 2.5T 2006 it's very close to the STI engine. Nasioc.com could be a good resource for you, but they are going to want even more data. :D
 
#22 ·
I have a boost gauge in my house, and when I log, I hook it up and hang it from my wiper as I have no place to mount it in the cabin yet. I've seen it spike to 15, then drop to 8, then creep to 11 (where it should be) in the upper gears.

I didn't log boost, don't really know what I'm doing yet with logging, but I'm sure the option is there. The Tactrix I'm using is borrowed, so I don't have access to it all the time, but I'm working on getting it back.

Snorkus delete is that thing in the fender that muffles the intake noises. Some people say it makes a difference to remove it, but I didn't notice one, and I've seen some dyno data that supported that.

Oil on the bulb means there was oil on the backside of the bulb in the MAF, indicative of blow-by in the engine, itself indicative of crappy previous owners that appear to have damaged a piston when they overheated the car. I thought cleaning that bulb might solve my issue, but it also made no difference.

The only codes I throw regularly are for the SAI system, pump stuck on, valve stuck open, etc. I plan to delete them from the ECU eventually since I need the space the pump occupies to mount my Grimmspeed master cylinder brace, but that's another thing I'm not comfortable with concerning the ECU just yet. For now I just keep a scanner on hand and clear them as they come in.

I mapped the throttle and throttle body one time, along with the error between the two, and everything was in order. Error was zero, and the both graphs were a match. The graph above is with the pedal flat on the floor the entire pull, I started it after WFO and ended it prior to redline, still WFO.

All of my NASIOC threads have died, this thread was dead, two dealership mechanics and the local Subaru gurus all looked at me like I was asking about the launch control on a Ferrari, seems they've not encountered this issue before.
 
#23 ·
Well you seem to have a "custom issue." Meaning the issue is unique to your car because of what has been done to it most likely before you even got it. Diagnosis of such issue is harder and time consuming.
I'm begging to wonder though if this isn't a burnt valve issue...
 
#25 ·
You definitely need to log boost from the logger. You need corrected manifold air pressure parameter selected in romraider gauge tab.

The graph you posted show the maf reading consistent with boost solenoid duty cycle indicating the ECU is pulling boost because it sees too much boost and then it try to add boost again. Your wastegate duty cycle table does not match the boost the engine supposed to see in that particular condition. Some other time it match and did not cause the boost cut like that.

Boost are not digital and hit the same every time. It depend on a lot of other things. If the map is not programmed correctly it would be very easy to mess up a lot of other things.
 
#26 ·
Just an update, when I did my turbo upgrade, I found a hole in the inlet the size of my pinky. A certain Subaru shop in Golden, CO actually thought that part was OK to reinstall on a customer's car. I replaced it with a Perrin, and although my idle still acts a little odd occasionally, most of my driveability issues have cleared up.
 
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