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The Stars At Night
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1,460 Posts
Discussion Starter #1
Soooo, I was coming back from Arkansas yesterday, I noticed on some parts of the drive the car would buck horribly. I actually noticed it more when I was on the gas a little cruising, then let off a small amount (read: the AFC was showing 12% throttle, back it off to 6-8%). It did it still when I would just let off the gas completely, though not as bad and not as often. Mainly when I would be cruising and just back it off a little. This just started yesterday, and it happens at all ranges of RPM. It did it when I was going 70 at 3200 RPM, at 20 miles per hour at around 2000RPM, so I know it's not just doing it when the RPM gets too low.

What could be the cause of this? Also, when I let off the gas now, even before I boost or anything, the RPM will hang at around 1800-2000 then drop to 1000 rapidly, hang for a split second and then try to die. Could a leak in the IC piping couplers cause this?

Setup:
DaveH PT52 kit
Tial 38mm atmospheric dump
Greddy Type-RS - not re-routed
stock fuel
3" exhaust through midpipe, stock backhalf


I tried to pull over and look at the car, but by the time it had started doing it, it was dark out and I couldn't see crap...I have yet to go out there and look at it today.

Thanks,

Bryan M.
 

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The Stars At Night
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1,460 Posts
Discussion Starter #3
But I have never head this problem before, and when it is the BOV I can tell, I mean at 12% throttle I'm not making any boost at 2000RPM. I also notice it from a start. If I start going if I just slip the clutch barely too fast it's like the car tries to die. It never did that before, it used to just bog a little, now it's like it tries to shut itself off.
 

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911 Turbo Now
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1,391 Posts
Well r ember BOV`s don't need to be in boost to open up, theyre going off the pressure from the FPR or the like. So it could be trying to open up so you don't surge.
 

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my rpm occasionaly bounces from a nice solid 1-2k to 700-0 every once in awhile when i let off the gas or slam the brakes. I think I have it down to a vac leak somewhere.
 

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I had the exact same problem on my NA-T sc300. On your intake manifold, check the vaccum hose on the TPS on the front of the manifold, on top the motor. I kept blowing it off from boosting. Same thing probably happened to you. Just replace it.
 

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The Stars At Night
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1,460 Posts
Discussion Starter #8
Do you happen to have a picture of where that hose is?
 

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Its dark out here right now, so I'll try to explain a little better. On the crossover of the intake manifold (part that goes over top of the motor), halfway down toward the right, there is a large, valve-looking thing. On the bottom of this, there is a vacuum tube. Mine would pop off, and I would get REALLY choppy and stutter at exactly 12% throttle in any gear, just like what you're dealing with. I'm sorry I can't be of any more help man.
 

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The Stars At Night
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1,460 Posts
Discussion Starter #10
I just got off work so I'll go check it out...but I'll mention this too...

I just now got back from work, having had to drive one of my dad's cars. I go out this morning to go to work, turn the car on and remember my hatch is open, so I get out to close it and within that first 10 seconds of idling, the car falls on its face, drops to probably 200RPM, I thought it had died, I couldn't hear anything for a good 1/2 second, then it pops back up and idled really rough at about 400-500RPM. I shut the car off and had to drive my dads to work because I was already running late. I'm about to go outside now and look at it.
 

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The Stars At Night
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1,460 Posts
Discussion Starter #11 (Edited)
Here is a video of what is happening...sorry for the horrible quality, I used my cell phone. When it starts up, it almost dies. I give it some gas to keep it going, the RPM then goes back up and idles fine, but when I give it some gas and it falls you can see it dies if I don't feed it some throttle. The vacuum lines look fine from what I can tell. The AFC connections also look ok as suggested on DFWMKIV.com...I'll take some pictures of under the hood at the intake/throttle assembly to see if you can help point out what could be wrong...


 

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The Stars At Night
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1,460 Posts
Discussion Starter #12 (Edited)
Ok...well I just got done messing with it, it's way to dark now...here are a few pictures I took:







A couple other things now...

After starting the car up and running it for just a couple minutes total, I absolutely reek like exhaust. It was never this bad even when I had a huge exhaust leak. I mean, I smell, I'm still smelling it on myself without even trying. Could something that is wrong with it cause it to idle way rich?

I realized just now after revving it so my parents could hear, when the RPM were dropping around 1800-2000 I could hear what sounds like a screeching sound. Not very loud, probably not able to catch it on video. In all honesty it could maybe just a belt or something squeaking, but it got me freaked out. Would I get a metal on metal screeching sound if my turbo was getting starved from oil? Would it make some sort of noise if it was about to die?

It now just seems like anytime I even try to hit the gas from idle, it wants to try to stall first.

I don't see how it can just start doing this randomly after running perfectly for so long? I've never had any problems with it at all?

Now I'm freaked out that it is something more serious...
 

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Ok, on the regulator looking thing behind the plug for the TPS, there is a vaccum hose that attaches to it. Check that, thats the issue I had with my car. It kept getting blown off. When I put it back on everything was ok.
 

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have you checked you MAF sensor? when mine died it acted like that when i started the car. it would be uber-rich and then die.
 

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The Stars At Night
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Discussion Starter #16
have you checked you MAF sensor? when mine died it acted like that when i started the car. it would be uber-rich and then die.
Little red flags are going off in my head because when I had it at the shop awhile back, they said it was "finicky and could die at any moment"...I blew it off because the car ran fine...how would I check to see if it was the MAF that was dead? Does anyone have an NA in the DFW area that could lone me a MAF for a day? I hope it is this...this would be such a simple solution...
 

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The Stars At Night
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1,460 Posts
Discussion Starter #17
Ok, on the regulator looking thing behind the plug for the TPS, there is a vaccum hose that attaches to it. Check that, thats the issue I had with my car. It kept getting blown off. When I put it back on everything was ok.
We are talking about the plug with the silver on it? All of the hoses back there look to be on...is it hidden a little?
 

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vanilla in her puddin'
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175 Posts
first things first check all your vacuum lines follow every one of them and look for cracks or leaks along the vacuum lines. Second check all your inter cooler connections make sure they are all tight and non are loose. Third take your BOV and reroute it back into the intake if its venting to atmosphere is only gonna stumble and die. Finally make sure that your fuel pressure is at 40-45 psi static. That means with no vacuum going to the regulator its at 40-45 ps.

IF that does not work take your maf and blow compressed air on it to clean to do not touch it and do not use any solvents.
 

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The Stars At Night
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1,460 Posts
Discussion Starter #19
first things first check all your vacuum lines follow every one of them and look for cracks or leaks along the vacuum lines. Second check all your inter cooler connections make sure they are all tight and non are loose. Third take your BOV and reroute it back into the intake if its venting to atmosphere is only gonna stumble and die. Finally make sure that your fuel pressure is at 40-45 psi static. That means with no vacuum going to the regulator its at 40-45 ps.

IF that does not work take your maf and blow compressed air on it to clean to do not touch it and do not use any solvents.
Already checked the vacuum lines, none are loose or off, and no cracks I could see.

Looked over the intercooler pipes countless times, none are loose, none of the couplers are punctured.

The BOV has always been vented to the atmosphere, I don't really have an easy way to reroute it to the intake.

How do I check my fuel pressure?
 

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The Stars At Night
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1,460 Posts
Discussion Starter #20 (Edited)
Not like anyone cares, but the car is running now...

When I first had the shop in Arkansas finish the oil return line, they told me the MAF was shot and I needed a new one. I got one from a forum member and had it sent to the shop. When I went to pick up the car, they told me the MAF I had was broken, and that the car could die because the MAF might fail at any moment. I assumed that he was referring to how the new MAF was broken and it could fail, but it never crossed my mind that he might be referring to how my old one was failing. I drove the car for 15k miles like this, never had any problems, until a few days ago. I couldn't figure it out, that is why I started this thread.

So I got a can of compressed air and went to go try and clean the MAF. I noticed some of the grill was bent...funny I thought, that's what my original one looked like. Didn't work. Then I thought to myself, hey, the shop said that the other MAF might work and might fail, but even if it works for a little, I could know that the MAF was the issue. So I go dig it up from my car parts box, clean it for good measure since it's been collecting dust for about 2 years, guess what, none of the grill was bent either...odd I'm thinking. Stick it on, go to turn on the car, it won't even turn over...ahhh, crap. Oh wait, I realized I was stupid and forgot to plug it in...yeah really smart. So then I go plug it in, turn on the car, it hesitates for a minute...great I think, the MAF isn't the issue. Give it some gas, and instead of wanting to die, it idles.

I'm in complete shock. I'm beginning to think they told me the new MAF was broken because they couldn't get the AFC to read anything, but that was just because they wired it incorrectly. I let it idle for a minute, let it warm up, back it out of the garage when I notice white smoke lingering. I get out of the car and it's putting out a constant white smoke, rev it, it puffs more. I go smell it and it reeks like gasoline. I'm curious, but I need to test drive it. I go take it out of the neighborhood and down to the gas station, get out, check for smoke again, none whatsoever. I boost it on the way home, AFC is still correcting, everything seems to be running well. It was a little wet out, and I tried to get on it in 2nd since I couldn't/didn't want to be going that fast. Of course, being wet, absolutely no traction at all. It feels stronger now though, maybe it's because I've been driving around in my dad's old 323i. Was it power shock or could it be pulling stronger because it could be lean? Anyway, I'm concerned now, so I'm going to try to schedule a time to get some dyno readings with A/F done so I can ensure everything is still good.

Lessons learned:

1. Supraforums help is amazing
2. Never trust shops ANYWHERE in Arkansas, no matter who know that recommends them
3. The Supra is still king

Here is a picture and video of the smoke when I first started it up...I guess my last question is, what could have caused the smoke? Could it have just been running pig rich with the broken MAF and it was just burning off the excess fuel in the exhaust?





Thanks all,

Bryan M.
 
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