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Old 05-26-2015, 05:00 AM   #1
FuelCell250
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Default M44 Long Term Fuel Trim 20-25

I just finished rebuilding my 1997 318i with the M44 and an automatic transmission. I replaced the pistons (MaxSil), rings, bearings, timing components, and seals.

I didn't drive it before rebuilding it, as I bought it needing the rebuild. I have about 500 miles on the motor now, and ever since day one I've been having these issues:

- Fast idle, around 1200 RPMs
- Long-Term Fuel Trim of +20 to +25
- Code: P0505 - Idle Air Control System
- Code: P1509 - Idle Control Valve
- Code: P1550 - Idle Speed Control Valve Closing Solenoid Control Circuit Electrical

Here's what I've tried:

- During the rebuild, I triple-checked for correct timing
- During the rebuild, kept a sharp eye out for cracked vacuum lines
- Replaced a severely cracked intake boot
- Cleaned the ICV (now it doesn't work, no buzzing like before )
- Cleaned the MAF
- Replaced the pre-cat O2 sensor ($175, old one was welded in, used plug and play Bosch part)
- Replaced the MAF with another used MAF ($110)
- Unplugged the crankcase vent and plugged it, thinking bad CCV

I'm not really sure what to try next. Any ideas?
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Old 06-21-2015, 09:22 PM   #2
FuelCell250
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I tried replacing the CCV, no difference.
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Old 06-29-2015, 03:02 AM   #3
xxxJohnBoyxxx
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Maybe replace ICV since you cleaned it and it doesn't buzz now. I know they buzz when they are good with ignition on and motor not started

John S
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Old 06-29-2015, 04:19 PM   #4
FuelCell250
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Since posting this, I've replaced the ICV (buzzes happily now and idles much better) and the CCV. The problems remain.
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Old 07-01-2015, 01:06 AM   #5
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What happens when your reset adaptions?
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Old 07-01-2015, 01:25 AM   #6
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Quote:
Originally Posted by bmwconnect View Post
What happens when your reset adaptions?
Not sure. Touch positive and negative cables together for 15 seconds to clear them?
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Old 07-06-2015, 12:27 AM   #7
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Quote:
Originally Posted by bmwconnect View Post
What happens when your reset adaptions?
Ok, I ended up testing this by leaving the battery disconnected for a few hours while working on another project.

For the first 10 minutes, the car ran horribly. Then it figured things out and started running smooth again.
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Old 08-01-2015, 11:43 PM   #8
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In town it's getting about 18 mpg. Ouch. The car also needs to pass emissions in 3 weeks.

I couldn't see where any other vacuum leaks could be from, so I took it to a BMW specialist and they smoked the intake. Unfortunately I couldn't be around when they smoked it. They identified two possible leak sources:

- Vacuum lines from the fuel injectors
- A leak from a possible crack on the DISA valve

I replaced the vacuum lines from the fuel injectors, and no change. That leaves the DISA valve. It's about a $280 part, non-OEM. I can't see any cracks on it (I didn't remove it). Has anyone had experience with this part failing, or what the replacement procedure is? It looks like the lower intake manifold has to come out, which is a real pain.
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Old 03-25-2016, 03:15 AM   #9
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This issue was resolved by replacing a weak fuel pump. You can find the details here.
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