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MEFI-4 Idle Hunt at Start Mystery

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OnPlaneDrifter

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[FONT=&quot]Hello experts,
Am struggling with a mystery.[/FONT]

[FONT=&quot]I have twin 2004 crusader 6.0s. On any start, hot or cold, the engine hunts for idle with wide swings. It settles eventually or if I give it a bit of throttle, it settles back quicker. It also happens when I throttle down in neutral, it hunts a bit before settling down. (RPMS are stable at anywhere over 1k). I changed the MAP sensors with no effect. I changed the IAC valves, it just made it worse funny enough. I really don't want to spend more on parts or buying a scanner. Are there any other usual suspects I missed? These engines perform flawlessly under load...this issue is more being picky but it drives me crazy.[/FONT]
[FONT=&quot]Any ideas? I was thinking about the coolant temp sensors but I am not getting any CEL and the issue occurs regardless of whether the engine is hot or cold.[/FONT]

[FONT=&quot]Thanks in advance.[/FONT]
 
CaboJohn said:
Both engines or just one has the problem?
Click to expand...

Both engines...starboard is a bit worse. I wonder...if the PCV valve is stuck open, would that allow too much air into the manifold causing the issue? The PCV valves are original... none of my research has suggested it but I'm wondering if it stands to reason?
 
1) If you don't have one, download a copy of the MEFI 4 Diagnostic Manual. Not hard to find for free and it is 337 pages of invaluable information. Of course they recommend a scanner but there is so much info on how the system works that you may be able to noodle through many problems.

2) As for the PCV valve, I would give it a maybe. Your IAC valve is just a motor controlled orifice that causes a small air "leak" into the intake manifold This is adjusted by your MEFI 4 to adjust idle speed. An uncontrolled leak from a PCV valve could mess this up. Quick check would be to pull the hose connection from the PCV valve going into the intake manifold and tape it over. If the problem goes away then change out the PCV valves.

3) The diagnostic manual will give you some more possibilities for problems with the idle speed. It is rare that such a problem would be on both sides at the same time. Maybe some sort of wear/corrosion issue in the distributors that built up over time. Have you messed at all with the distributor position vis a vis the manifold? In your engine I believe that (loosening the clamp and rotating the distributor) adjusts "cam retard" and not engine timing (that is controlled by the MEFI 4). Difficult to get the retard reset correctly without a scan. But when it is off, you will get issues with the either idle or the high rpm spark consistency, depending upon which way (+ or -) you are out of adjustment.
 
2x John's advice in post #4.

the scanner will let you see what the MEFI sees and is the fastest way to resolve issues.

To expand in the 'cam retard' point, if its incorrect you will 'have drivability issues' which means all kinds of irritating symptoms. if you haven't touched the distributors, DONT...until you get a good scanner to set the cam retard value...

you can see if the PCV valve is leaking too much air, at idle, by just pinching off its hose.
 
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