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nsn nsn is offline
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Rough idle and P1124 & P1126

Hi everyone,

My car is Boxster 1997 and its running quite rough idle. Also I get dtc codes P1124 & P1126 which fuel enrichment level issue, which I guess is most often air leak somewhere, is that correct? Sometimes idles stalls so much that engine stops fully.

My question now is, is it safe to drive the car? I heard that if its AOS, it can be dangerous. If I clear engine codes/keep battery of for 10 minute it runs fine for a while but then after some time of driving I get same errors again and idle is rough.

Also is there anything easy things to check before I get it to dealer? Its quite hard to find vacuum leaks without any tools. I cleaned throttle body while ago, but no help at all. Also I changed maf, but that didn't make any difference.

Thanks,
NSN
Old 04-22-2011, 10:13 AM
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When checking for vacuum leaks you can use carb cleaner and spray around the vacuum lines.
If engine rpm rises then you have found the location of the leak.
Hope that helps!
Old 04-22-2011, 01:03 PM
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nsn nsn is offline
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Thanks Rockster,

Will do that after eastern.. when shops are open again.

Today i noticed this behavior, cold start in the morning, drive 1 hour, works perfectly and also lot of traffic light idle. Then stop car, wait for 15 mins, start it and idle is going up and down and car is almost dying.

Strange but i guess in the morning cold start parameters are different and somehow it works fine all the time. Then next start is warm one with different ecu parameters and there we are, rough idle.

Thanks,
nsn
Old 04-23-2011, 02:11 AM
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Originally Posted by Rockster View Post
When checking for vacuum leaks you can use carb cleaner and spray around the vacuum lines.
If engine rpm rises then you have found the location of the leak.
Hope that helps!
I've never been a huge fan of the spraying carb cleaner on the hot engine. It always seemed like a recipe for disaster (fire).

-Wayne
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Old 04-23-2011, 12:59 PM
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Quote:
Originally Posted by Wayne at Pelican Parts View Post
I've never been a huge fan of the spraying carb cleaner on the hot engine. It always seemed like a recipe for disaster (fire).

-Wayne
It's been recomened to me, by some guy named Harry. To use brake cleaner. Same results and safer.
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Old 04-23-2011, 07:08 PM
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NSN, if you find no vac. leaks, take apart your throttle housing. Clean as you would with carb. cleaner also clean the maf with some some CRC maf cleaner. Mine as never run better since I did, I also had very rough idle and stall.
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Old 04-24-2011, 07:43 AM
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Originally Posted by randy_k View Post
It's been recomened to me, by some guy named Harry. To use brake cleaner. Same results and safer.
I try to stay away from all of that stuff as much as possible. Supposedly brake cleaner contains tetrachloroethylene which can break down into phosgene as detailed in this alarming tale: Brake Cleaner = Phosgene Article

-Wayne
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Old 04-24-2011, 11:57 PM
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Not going to use brake cleaner then, actually took car to local indie garage anyway.. with a tow car.

Drove over very small bump, those normal bumps on roads and heard *snap*, pulled over, look everywhere and didn't notice anything. Back to car, first gear in, nothing happens, car doenst pull at all. After that I got off the car and found out that drivers side drive-shaft is completely off from gearbox. Engine was running fine all the time.

This car has been a nightmare to me (starting from rebuild), it looks to continue, still like it though. ;-)
Old 04-25-2011, 12:47 PM
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nsn nsn is offline
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Getting my old thread back up. Drive shaft is fine now but idle still causes issues. I am running pretty much out of ideas now, no air leaks, new throttle body parts tested, fuel pressure ok (local indy porsche garage did that). Still same thing idle jumps up and down when engine is warm.

Any ideas what to try next?
Old 07-01-2011, 04:47 AM
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Fuel pump? It is the common element in the 2 codes causes lists.
Old 07-02-2011, 10:49 AM
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Still no luck, I went through every single connection looking for any kind of leaks. After that (1 week), I haven't got any error codes but idle is still bad and sometimes when doing warm start its just dies off right away.

Now question, if i change this sensor in figure 2:
Pelican Technical Article: Boxster Engine Sensor Replacement - 986 / 987

How do I need to be prepared? How much liquid comes out from that sensor hole?

If this doesn't help I go for fuel pump..

Thanks,
nsn
Old 07-19-2011, 05:23 AM
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You could try disconnecting the mass air flow sensor at the wiring haness connection. I've heard the car reverts to stored lookup tables when it can't communicate with the MAF. If the car runs much better when it's not connected it would point toward a bad MAF sensor. Replacing the MAF fixed similar codes on my car. I did find some intake leaks but the real problem was the MAF.

Disconnecting the MAF is so easy it's worth a shot.

If you really want to find a leak, take it to a shop that has a smoke test machine. They inject smoke under slight pressure into the intake system. It's the scientific way to find intake leaks. The place I took my car only charged $75.
Old 07-19-2011, 11:22 AM
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From Loren over on Renntech:
"P1124 - Oxygen Sensing Adaptation Area 1 (Cylinders 1 - 3) - Rich Threshold
P1126 - Oxygen Sensing Adaptation Area 1 (Cylinders 4 - 6) - Rich Threshold
The ODB II manual says that these codes indicate your fuel mixture is too lean. That is, the DME can not make the mixture rich enough - i.e. rich theshold exceeded.

It lists as probable cause:
Intake air system leaking.
Fuel pressure too low.
Fuel pump volume too low.
Fouled fuel injectors.

There is a TSB 4/00 03.. Oil Filler Cap (dated 3-24-2000) that states: "If the oil filler cap is not fully engaged, or is tilted, (not engaged on both sides) the filler cap o-ring will not provide a complete seal. This can cause a CE light and Pcodes: P1124, P1126, P1127, P1128." This would be my first try.

If that is not it. You can likely rule out the last one (since you got codes for both sides) - as a having a fouled fuel injector on each side of the engine is very unlikely.
I would look for loose or worn vacuum hoses or other manifold leaks. You might also replace your fuel filter if you have not replaced it in the last 30,000 miles. "

An intake air leak could be a bad oil fill cap, bad AOS, bad gas cap, failed vacuum tubing, cracked oil filler tube, torn rubber intake etc. These are your most likely fixes. A process of elimination will find it. A bad fuel pump or fuel filter is possible but less likely. If it were my car I would go back to that "I cleaned the throttle body" and re-trace my steps looking for a cracked, torn or disconnected tubing or fitting.

+1 on avoiding combustible leak detectors: propane, carb cleaner, brake cleaner etc. Engine flash fires are fun but no fires are better. Been there done that;^)
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Last edited by Cajundaddy; 07-19-2011 at 12:52 PM..
Old 07-19-2011, 12:39 PM
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Thanks guys! Maybe I should explain what I have already tried. Engine is 6000km from rebuild, and first 5k went fine.

What's being done after issue with the idle:
*New maf (also tested with 2nd one)
*New coils + plugs
*Searched air leaks twice with steam machine by local indie.
*Fuel cap & Oil cap
*New AOS when rebuild (Doesnt smoke and oil cap can be removed after driving -> no extra vacuum).
*Fuel pressure checked with new regulator
*Idle motor tested with new part
*Throttle housing cleaned

After all that it looks like I dont get mixture error codes anymore, but I still get rough idle when engine is warm 180F-> Also warm starts are hard, quite often it starts but dies right away.. to go around that I need to rev it for 30 secs or so. When driving.. no issues, pulls nicely with every gear.

Whats not being done/checked:
* Fuel side, fuel pump, fuel filter.
* Oxygen sensors, durametric gives normal values though
* Other sensors, just reading from that sensor changing article that temp sensor adjusts mixture when engine is warm. That made me think about changing it. Its cheap part too.. so nothing really to lose. Just would like to know what happens if I take sensor out.
Old 07-19-2011, 01:27 PM
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Quote:
Originally Posted by nsn View Post
Thanks guys! Maybe I should explain what I have already tried. Engine is 6000km from rebuild, and first 5k went fine.

What's being done after issue with the idle:
*New maf (also tested with 2nd one)
*New coils + plugs
*Searched air leaks twice with steam machine by local indie.
*Fuel cap & Oil cap
*New AOS when rebuild (Doesnt smoke and oil cap can be removed after driving -> no extra vacuum).
*Fuel pressure checked with new regulator
*Idle motor tested with new part
*Throttle housing cleaned

After all that it looks like I dont get mixture error codes anymore, but I still get rough idle when engine is warm 180F-> Also warm starts are hard, quite often it starts but dies right away.. to go around that I need to rev it for 30 secs or so. When driving.. no issues, pulls nicely with every gear.

Whats not being done/checked:
* Fuel side, fuel pump, fuel filter.
* Oxygen sensors, durametric gives normal values though
* Other sensors, just reading from that sensor changing article that temp sensor adjusts mixture when engine is warm. That made me think about changing it. Its cheap part too.. so nothing really to lose. Just would like to know what happens if I take sensor out.
Clean and balance your fuel injectors are a logical next step if you are confident in your other troubleshooting measures.
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Old 07-19-2011, 01:44 PM
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Old 07-19-2011, 01:44 PM
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