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Old 04-29-2013, 02:14 PM   #1
RP31
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Default Car starts fine when cold, then dies at stops when warm

This all started yesterday without warning. Started the car around 11:00, began driving, no indications of any problems. Even came to some stops without issue. Then when the engine was warmed up and I was rolling to a stop, I pushed in the clutch, and the RPMs dropped all the way down and the engine died. When I tried to restart, it was extremely difficult. When cranking, it sounds like the engine is spinning very slowly, and the dash lights get dim. Often times I am not able to get it started in a reasonable amount of time, and I have to keep the gas pedal pressed to get it to start. Once I do get it started, I have to immediately start revving the engine or it will die again. I basically have to crank and crank and when it finally fires, launch from a stop. Otherwise it will die. But if I let the car sit for a couple hours and totally cool off, it will start up and drive fine until it's warm.

To me this initially seemed like a battery issue, but I took the battery to Autozone and they say it is fine. However I have read at least one story about batteries testing fine even though they are bad. I have been doing lots of searching and it seems like this could be anything from a dirty MAF or TB, to a vacuum leak, a dying front O2 sensor, fuel pump, or alternator.

There have been no CELs. When the car is running, the battery voltage display on the SM3 reads around 13.6 volts. I would think if this were an alternator issue, it would be reading lower.

It is obviously heat-/coolant temperature-related in some way, but I cannot figure out what sort of mechanical or electrical problem could have just developed that would cause this to happen. The car has been running fine for the past week.

More background: About 2 weeks ago I had another dying engine problem that ended up being bad camshaft position sensors. I replaced both of those sensors as well as the crank position sensor, and also checked for corroded cables, cleaned all corrosion from all contact points and terminals, and added the Davenow grounding mod. After that the car was starting, running, and idling great with no issues. When I was doing that I also cleaned the MAF, so I would not think the MAF is the issue now. I do have a WBO2 mounted post-turbo, and it is reading fine. I have noticed that the front O2 reading on my SM3 will sometimes vary by as much as 2 from the WBO2 reading, but only when the WBO2 is more on the rich or lean side. I honestly cannot recall if this is normal or if it might be initial signs of a failing front O2, but I do know that the front O2 is not really reliable outside of a normal range, so maybe this is normal.

I've had the battery checked, I will get the alternator checked tonight, I have cleaned the throttle body, and I have checked for vacuum leaks. Just looking for any additional input on things to check. I'd really like to resolve this quickly. Having a car that runs, then leaves you stranded, then runs, then leaves you stranded a week later, is going to drive my wife to set fire to my car!

I could list out mods but they are extensive and since nothing has changed in a week (I've even been using the same gas station and the weather has been about the same), I won't bother with them unless someone really thinks they'd be helpful.
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Old 04-29-2013, 02:38 PM   #2
GravityDefyingSTI
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Maybe a coolant temp sensor
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Old 04-29-2013, 02:43 PM   #3
RP31
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Thought about that, but I would expect a CEL or a funky reading on the coolant temperature gauge, right? From what I have seen the gauge is operating as it always has.
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Old 04-29-2013, 02:46 PM   #4
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Not so, only if it's a 4 pin sensor will the gauge be effected. If its a 2 pin then the gauge gets sig from another sensor.
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Old 04-29-2013, 02:53 PM   #5
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A coolant temp sensor that is bad would read neg 40 which would make the car run rich as hell. If that was the case it would crank fast not slow do to fuel washing out the rings. Not sure what would help me help you so I will start with basics. How is the coolant level. Does the car smoke after is restarts cold?
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Old 04-29-2013, 02:56 PM   #6
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Coolant level is fine, car does not smoke after cold or warm start.
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Old 04-29-2013, 03:07 PM   #7
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OK good. I will post in a bit
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Old 04-29-2013, 11:29 PM   #8
RP31
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Got the alternator tested and it turned out fine. Also checked the coolant temperature sensor - it's a 3-pin.

I've had the battery hooked up to a trickle charger since I pushed the car into the garage last night... Charger says it is fully charged now. I will start the car tomorrow and just let it sit in the garage idling until it warms up and see what happens. Maybe I'll get a CEL or find a code pending.

Last edited by RP31; 04-30-2013 at 01:44 AM.
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Old 04-30-2013, 04:24 AM   #9
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Not sure how to tell you via this forum how to diag your car. When.you are driving cold and hot how does it perform.....besides stalling at lights. Is it pinging hesitating Any info would be helpful I just don't want to send you on a wild.goose chase in the wrong direction.
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Old 04-30-2013, 08:05 AM   #10
RP31
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Regular driving with the car actually moving forward is fine, cold or hot. I was discussing this problem with the guys at the auto parts store yesterday and told them "If I could keep the engine temp at 100 degrees the entire time, or just get on the highway and drive, you'd never know there was anything wrong with it." Acceleration and AFR are just as they have been in the past.
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Old 04-30-2013, 08:55 AM   #11
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So I just got done letting the car idle in the garage. I started it, let it come up to operating temperature, and then sit for another 5 minutes or so, just revving it once in a while. It never died. I have not taken it out of the garage yet.
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Old 04-30-2013, 08:58 AM   #12
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OK keep us posted and be careful who/what advise you actually listen to. That's geared At your part store guys. Maybe one of them has a clue but usually not.
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Old 04-30-2013, 09:00 AM   #13
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Go for a ride, do a wot pull only to hit full boost.... not redline. Report back with af reading. ..
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Old 04-30-2013, 09:02 AM   #14
RP31
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Quote:
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OK keep us posted and be careful who/what advise you actually listen to. That's geared At your part store guys. Maybe one of them has a clue but usually not.
Yeah they were really stumped and just throwing out things like coils and the ECU. They are very interested though and asked me to come back and tell them what the problem is, if I ever figure it out.

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Go for a ride, do a wot pull only to hit full boost.... not redline. Report back with af reading. ..
Will have to do that later today. Rush hour now and I live on a long stretch of 30 MPH road. Not going anywhere fast.
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Old 04-30-2013, 05:51 PM   #15
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You have all the classic symptoms of a dirty throttle body. I suspect you have around 80K miles, gunk builds up on the bore and cold idle is high enough to stay good, but hot idle closes the throttle more, and then you stall. Clean the throttle body and you should be fine.
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Old 04-30-2013, 05:54 PM   #16
RP31
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Yeah, that was my first thought too as I was stuck in the Penske truck rental parking lot, searching the site with my phone. But I took the throttle body off and cleaned it, and it's still acted up. Sorry, I should have included that part in my first post. Yep, that was one of the first things I did.

Edit: Actually it looks like I did include that in my first post. But I also created a word castle in my first post, so I apologize.

Last edited by RP31; 04-30-2013 at 06:04 PM.
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Old 05-15-2013, 08:46 AM   #17
RP31
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Forgot about this thread but I have not made any real progress on troubleshooting. Borrowed a car and recently moved to a new house, so getting the STi running again is very low on my list of things to do.

I did, however, order a new OEM coolant temperature sensor, which I will pop in this weekend and try to see how it goes.
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Old 07-14-2013, 07:00 PM   #18
RP31
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Holy crap my car has been sitting for a long time.

So, here's the update... I did install the coolant temperature sensor and nothing changed. I had some free time this afternoon so I hooked up the laptop and started the car in the garage.

Then it happened. Finally, a CEL! Never been so happy to get one of those. ECU is throwing P0030, which points to the front O2 sensor. I did notice that even when the car is fully warmed up now, with the TXS Tuner WBO2 reading 14.7 (about 6" post-turbo), the front O2 is reading 11.1 in RomRaider and on my SM3.

I don't know, I didn't notice this O2 sensor behavior before, and being unable to start/drive the car at all seems a bit extreme for an O2 sensor going bad, but maybe it's exacerbated by the different engine and tune. Thoughts?

I am going back out there to pull the air box and check the sensor wiring. I don't think this sensor has more than 20K on it. Also will review the RomRaider logs I took during this whole event.
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Old 07-24-2013, 11:15 PM   #19
RP31
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Well I replaced the front O2 sensor and it's definitely reading properly now, and the CEL went away.

But the car still can't make it out of the garage once it's warmed up.

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Old 07-24-2013, 11:38 PM   #20
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Check the IAC
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Old 07-24-2013, 11:57 PM   #21
RP31
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The lack of an IAC definitely is not the problem.
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Old 07-25-2013, 01:31 AM   #22
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Friends car had similar problems, was the fuel pump. When it dies next time have a buddy restart the car while you get under the car and beat on the fuel tank with a 2x4. If it starts when you hit it, probably the pump.
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Old 07-25-2013, 07:18 AM   #23
RP31
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I can try that. But when I turn the key I can hear the fuel system pressurize (and the gauge confirms pressure). That would rule out the pump, wouldn't it?

Again, very strange... Last night when trying to restart it there were times when it would not even try to crank. Like I was trying to start a car that had no battery. What could cause such a thing? I replaced the starter relay, but maybe the clutch switch needs to be checked. Not starting when hot is less of a problem than not staying running though.
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Old 07-25-2013, 01:21 PM   #24
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Quote:
Originally Posted by RP31 View Post
I can try that. But when I turn the key I can hear the fuel system pressurize (and the gauge confirms pressure). That would rule out the pump, wouldn't it?

Again, very strange... Last night when trying to restart it there were times when it would not even try to crank. Like I was trying to start a car that had no battery. What could cause such a thing? I replaced the starter relay, but maybe the clutch switch needs to be checked. Not starting when hot is less of a problem than not staying running though.
Check the ground underneath the coolant header tank, that's where the ecu gets its' ground from. Follow it back and make sure the wiring isn't damaged and ensure that it is actually grounded.
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Old 07-25-2013, 01:28 PM   #25
RP31
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Quote:
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Check the ground underneath the coolant header tank, that's where the ecu gets its' ground from. Follow it back and make sure the wiring isn't damaged and ensure that it is actually grounded.
That is an interesting idea. What do you mean by "header tank" though? Would that be the expansion tank on the passenger side, the overflow tank on the driver side, or something else? I noticed you have a '12 and I am not familiar with their engine bays so my descriptions may be off.
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