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g00b86 g00b86 is offline
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Default Cold start stalling & light throttle oscillating - 06-30-2020, 11:11 AM

Hello All,

Long time listener - first time caller.

Short and to the point. After doing VC & gasket at 190k I've noticed two issues that I cannot completely troubleshoot and hoping you folks might help point me in the right direction with respect to data logging.

The two issues might be completely separate or they may be related. I am thinking they are related but I digress.

Its summer here in NJ and its hot and humid even at 6:30am. When I first get in the car to go to work maybe 50% of the time the cold start issue occurs. When I leave for lunch after my car is sitting in the sun for hours it 100% of the time occurs.

The symptom is the car has erradic idle flucuations to the point of near stalling. It takes about 90 seconds to clear up on its own - or if I apply light throttle to 1000 RPM and let off it will clear up on its own. Having AC ON or OFF does not impact this. If I turn the car off an turn it back on the issue is gone. I have tried letting the car self prime since this is an 07 and it does not seem to make a difference as far as I can tell. There are NO Codes stored. No misfires stored when checking with INPA and my Autel AP200.

The car has had a HPFP replaced prior to my ownership somewhere around 70k as well as index 12 injectors around the same time. It has had coils replaced 2x and I replaced plugs when doing the VC. The car is 100% stock. No tune and no performance parts. I have to dig back through my records but lets assume both the HPFP and the injectors have atleast another 120k miles on them. The coils maybe have 50k on them.

My thought was leaking fuel injector. I need to pull plugs and see if any are wet, but one thing I would like to note is that during the VC install I had to index one injector like 10 DEG because it would not clear the VC to remove it. I just loosened the bolt and spun it. Would this be enough to damage the seal if I did not remove the injector?

Another thought was vacuum leak since I replaced a bunch of old vac lines during the VC install. I used almost an entire can of brake clean searching everywhere I thought was possible, including the diverter valves, the valve cover itself, the wategate solenoids and the vaccum canisters.

I have been using my Autel AP200 to look at HPFP and fuel trims during cold start as well as cruise and I am not sure what exact criteria I need to be looking for as far as an anomaly is concerned. I have compared my data to others here who have posted their logs and I think perhaps the AP200 is the wrong tool for this job. I did reset my adaptations and nothing changed.

My second issue is that in 3-6th gear (6MT vehicle) under light throttle at almost any RPM between 1500 and 2500 the car surges horribly. Like its being tugged or pushed hard. The RPMs do not fluctuate in any amount that I can read on the tachometer, so it does not feel like clutch slip. It is 100 cyclic and can go on indefinitely. So much so that it makes highway cruising nearly impossible. I have to vary throttle or the tugging sensation gets nauseating. I have read a few older threads here, and on several other forums about surging and no one ever replies back with a definite resolution.

I am hoping someone can provide what data I should be logging and posting here to get more involved in trouble shooting. The car is very high milage, but well maintained. I have addressed all the basic "consumables" on the N54 and I would really be hesitant to throw money at a bunch of parts if I can't first isolate where the problem is coming from.

Do many people experience a 2nd HPFP failure without any codes? Do index 12 injectors need to be replaced AGAIN at high milage? Would coils fail without misfire codes or signs of failure? Thanks to all who read this far and any input you may have!
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g00b86 g00b86 is offline
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Default 07-01-2020, 03:33 AM

Tried picking up an MHD WiFi adapter to attempt to data log and it looks like they are out of stock everywhere until mid July.

Taking the plugs out today to read if it is injector related. I’ll post back my findings.
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sbonomo sbonomo is offline
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Default 07-06-2020, 11:08 AM

Bookmark - i am having similar issues.
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g00b86 g00b86 is offline
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Default 07-06-2020, 12:31 PM

Just a status update-

Took the car apart over the holiday weekend. Found several vacuum lines worth replacing, which I have. Checked all the bolts on the VC and nothing obvious with respect to a vacuum leak.

Checked the plugs and #1 was actually very white/lean so my thoughts of a leaking injector are out the window.

Checked all grounds and batter + cables everywhere I could. Alternator, starter and the DME area junction. Nothing out of place. Scrubbed some of the oxidation off the terminals but nothing worrysome. The B+ cables were replaced 2 or so years ago.

Ran a more involved scan of the car and i was getting error codes leading to the CAS. A0b4 related to starter operation
A0C1 for terminal 50 output
A0C2 CAS output terminal 50 RS
D904 K-CAN line fault

Checked into these codes and nothing conclusive with all 3 but I might just remove the CAS and see if the components inside look OK as I have read there is a known failure in the unit.
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g00b86 g00b86 is offline
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Default 07-07-2020, 05:53 PM

Vacuum lines and battery checkup seemed to have cleared up the cold start issue so far.

The oscillations while under load are still there. I am still searching for a solution.
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g00b86 g00b86 is offline
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Default 07-20-2020, 10:23 AM

Small update again - collecting parts for walnut blasting but its just too hot right now to perform. Have not been driving the car.

While troubleshooting I accidentally left one of the vacuum canisters disconnected and drove the car maybe 10 miles by accident. I did not have any idle nor light throttle oscillations so my next best guess could be a bad boost solenoid. Oddly tho - the car threw no codes. I just realized this morning when i went to take the car to work and noticed them disconnected.

The symptoms do not seem synonymous with what others reported for bad boost solenoids either.
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Dave @ BMS/Fuel-It! Dave @ BMS/Fuel-It! is offline
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Default 07-21-2020, 05:52 AM

You could always pick up a cable while waiting for the WiFi adapter.

Logs really help in a scenario like this


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