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Old 06-08-2012, 05:51 AM   #1
alcoolaid
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Default 07 STI Won't start or rough idle when it does start

So here is the story. I have done so much diag it is making me frustrated. Not my car but my friends 2007 STI that I have done work on.

One day a few miles from home, friend started his car and it idled very rough. Sounds like its running on 3 cylinders. If you give it throttle smooths out a bit but still very rough. Off the gas pedal and letting it idle, 1500rpm cold, barely gets -5 vacuum. But it will idle on its own when it starts. NO check engine light. Friend limped it home a few miles running rough.

Thinking it's a coil pack or spark plug, I move coil packs around first on the car and still same issue. Sometimes car won't even start at all. Put different spark plugs in the car, still same problem. Either no start or starts after 20 attempts here and there. Throw on my coil packs and still same issue. Changed the battery still same issue.

When it idles bad, no smoke from exhaust or anything like that. No blow by, oil level good, etc.

Did a compression test, 170psi all around. Checked for vacuum leaks, none at all.

Car has CP forged pistons, arp head studs, intake manifold spacers, ported throttle body, grimmspeed ebcs, catless dp, exhaust, ks tech 73mm CAI, stock injectors, walbro 255, 1 step colder NGK plugs, dyno tune. Car was running for many thousand miles no problem and suddenly this occurs.

Only thing that stumps me is, how can it be a fuel pump or something if the car starts and idles(rough)? And what is causing it to NOT start on many occasions? Fuel pump primes every time I turn the ignition, I hear fuel circulating through the fuel rails. When the car runs it smells pretty rich but could be just warm-up enrichment.

I was thinking maybe injector but even if one was stuck closed or open it should still start. But it doesn't start until after many attempts. Sometimes it will start on back to back tries and idle rough and some times it won't start after like 10 times. Can't be crank angle sensor or cam angle sensors as the car doesn't throw a CEL when engine is running. And if one of those were not working, the car should never start. I am out of ideas.

I have a video that I will be posting soon.

CN: Car has problems starting, when it does start, idles really bad (like on 3 cylinders)
Swapped coil packs and changed spark plugs, same issue
Fuel pump is priming and can hear fuel circulating
Compression test done, 170 psi all around
No vacuum leaks
Unplugged the MAF, still same issue
Unplugged the primary 02 sensor, still same issue
Possibly injectors? But why no start on many occasions?
Possibly fuel pump going out? But why does it start and I can rev it up to 3k and still goes
Bad gas? Filled up $20 gas on the way home while limping it
....out of ideas...
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Last edited by alcoolaid; 06-08-2012 at 06:07 AM.
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Old 06-08-2012, 06:11 AM   #2
alcoolaid
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Old 06-08-2012, 12:38 PM   #3
Rev Works
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I would try swapping out the MAF sensors and checking the injectors. Make sure none of the o-rings on the injectors haven't deteriorated or split. Also, try spraying some brake clean around the engine to see if there are any leaks you may not have noticed.
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Old 06-08-2012, 02:21 PM   #4
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Few things I notice:
Hardly any manifold vacuum, probably compensating for a dead cylinder.
High compresssion (should be closer to 145)

The first step is to get a laptop with tactrix cable and log the roughness monitor to see what cylinder is causing the problem. This will also give more data to help troubleshoot.
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Old 06-08-2012, 02:24 PM   #5
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fuel pump controller or fuel pump.

Can you get a fuel pressure gauge on there?

Logs will tell you if it's rich or lean.

There is an o-ring in the fuel filter in the tank that is known to blow out on occasion.
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Old 06-08-2012, 06:29 PM   #6
alcoolaid
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Thanks for the replies.

Out of my bad luck I sold my tactrix cable since I didn't use it for like 3 years...

Going to see if my friend can borrow one.

I knew I was going to need it to diag some more but was just hoping I could figure out.

Low vacuum at idle means more fuel pressure at the rails too... Wonder if that might have a bit to do with it. Still shouldn't make it idle like that though. Will report back with ecu findings.
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Old 06-09-2012, 07:15 AM   #7
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off topic but does your odo say 16,xxx miles/km? That car is like mint! Hope you get it fixed.. if it was an o ring or faulty fuel injector check for odors around the fuel rails and under the rear seat where the fuel pump is
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Old 06-10-2012, 09:04 PM   #8
alcoolaid
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Doing diag right now.

Romraider logs look like misfiring all cylinders via roughness monitor.

Air fuel is 14.7....

Then got dtc/cel for cam timing correlation a and b or something. Just took rad and timing belt covers off and timing is perfect! What the hell?!?

Avcs problem? I took the filters out of the banjo's when I rebuilt engine...

And yes that is 16k km's

What next...
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Old 06-10-2012, 09:07 PM   #9
alcoolaid
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In addition I noticed when I bring revs higher like to 3k things smooth out but still a bit rough
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Old 06-10-2012, 10:59 PM   #10
alcoolaid
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New video I just took. You can see when I hold the gas down a bit to hold a 850-950rpm idle AF correction #1 is like 10+%.... vacuum leak still possibly?

When I hold the revs up it smooths out a lot...

Time to go back to friends house tonight with brake clean and spray whole intake manifold with engine running I guess
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Old 06-10-2012, 11:10 PM   #11
alcoolaid
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Can't believe I didn't see it earlier. Right bank is reading average 59-60 degrees advance and left bank is reading around 62-64 degrees advance....

AVCS problem I think. I removed the filters when I rebuilt this engine though. What the hell!!

I'll unplug the solenoids and see what it reads. If it's still reading advanced.... mechanical problem for sure.... or cam sensor
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Old 06-10-2012, 11:23 PM   #12
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Sounds like the problem I had with my 07 conversion, problem was I had
the vacuum lines reversed to the wastegate control solenoid valve.
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Old 06-11-2012, 03:19 AM   #13
alcoolaid
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Figured it out.

Took out the avcs solenoids and they were both stuck a bit open. Cleaned them up and started right away with no idling problem!

Friend needs an oil change ASAP and hopefully will never happen again...
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Old 08-24-2015, 04:38 PM   #14
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Default need help with similar idling problems..

Quote:
Originally Posted by alcoolaid View Post
Figured it out.

Took out the avcs solenoids and they were both stuck a bit open. Cleaned them up and started right away with no idling problem!

Friend needs an oil change ASAP and hopefully will never happen again...
Hey alcoolaid, this is a bump.

I sent you an e-mail regarding this engine idle issue. Please reply back a.s.a.p!!
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