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Discussion Starter #1
Hey all, I have a 97 with a 4.6 PI motor. It is idling pretty rough and sometimes when under a light load it will stumble and seem to want to stall out. I was recently in a drive through and the car died when I tried to turn the wheel at rest. I just changed the plugs and wires, coil packs are about 3 years old, I cant find any vacuum leaks, maf is clean, IAC is new , all O2s are new, and fuel pump is relatively new. I have an xcal2 and datalogged my fuel trims and there aren't any instances where the adjustment is over 10%. Also just tested compression and the highest was about 148, lowest about 141 and there were no oil fouled or fuel fouled plugs. I'm pulling my hair out here trying to figure it out. If there is something else I should be datalogging let me know and I'll do it, that area just isn't my forte.
Thanks for reading my book, please help.
 

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Fuel trims ideally should only be 2-3 percent off across the board (Both LTFT and STFT) when in closed loop - if you get on the gas the STFTs will show commanded lambda (the desired A:F) - some number usually between .8 and 1.

In any case - I get this with the T-bird mainly because of the cams. In short, there's too much EGR in the cylinders and I have a hard time giving it enough spark to keep it from misfiring. It's always possible you're getting more EGR than you should and there isn't enough spark to compensate.

Datalog rpm, airflow #/min, spark source, spark advance, IAC duty cycle, and ISC integrator. Let us know what you find.
 

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Discussion Starter #3
Okay so I datalogged what you suggested, I just don't know what I should be looking for. I attached 2 datalogs The first is start and idle, the second you can see I bumped the throttle, then went from park to reverse, to neutral, to drive, to park.
 

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Can you upload and send me the .csv files? Did it stumble at all for you during either of those runs?
 

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Well, the idle airflow values in the tune are a little off but not so much that the PCM isn't compensating like it should be. IAC duty cycle looks good as well.

Spark looks like it's where it should be; fuel trims indicate that the PCM is having to add about 3% more fuel than programmed at that RPM range, but again - within tolerable limits. There are other things that could be logged but I don't know how much more insightful it would be at this point.

In short - I didn't see any smoking guns in the info I saw to indicate what would be causing it to idle rough. It's probably an A:F imbalance but I can't be sure.

Try a couple more simple things. Unplug the battery for several minutes to reset the memory in the PCM - observe the idle behavior with the MAF unplugged, unplug all the vacuum lines to the plenum (except fuel pressure regulator) and tape them off and observe again (with MAF attached if it doesn't get better with it unplugged).
 

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Discussion Starter #7
Thanks for checking it out! I'll definitely try everything you mentioned, and hopefully find the issue soon. This idle is driving me crazy.
 

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Discussion Starter #8
I taped off the vacuum to the EGR and holy hell it idles much smoother. I still feel like I'm getting a bit of a miss. Every once in a while it will seem to skip a beat so to speak. I have no codes btw but it seems to be an excessive egr issue for now even though its all pretty new. I'll swap some stuff around and go from there. Thanks for the help.
 

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Could be one of a few things there - a leaky vacuum line along the EGR path, a leaky solenoid (letting vacuum through to the diaphragm), or a diaphragm that won't close all the way letting a certain amount of EGR in at all times.

Good to see you found the path to chase. :)
 
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