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Discussion Starter #1
I've been hunting for vac leaks for some time now. Rough idle, flares and fades, stumbles in OD low RPM. There is definitely a vac leak at one of the tiny holes around the bottom of the EGR valve disk. Is this normal? I've tested the valve by putting vac on the diaphragm and the valve opens, closes, and holds air pressure. I place finger over one of the holes and there is definitely vac leak. Anybody know? Would this be a likekly cause of the idle issues?
 

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What year is your truck and what engine? Sometimes the IAC valve gets plugged up on the 4.0's and causes rough idle as well.
 

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Engine helps a lot, can only diagnos what we know.

The 5.0 will crack the EGR tube if it's the original ribbed one. What hole are you placing your finger on? Any vacuum leak will cause idle issues as it is unmetered air into the engine.
 

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Discussion Starter #4
Turns out the leak was due to the last mechanic failing to put a gasket between the EGRv and the EGR tube. Inserted the gasket yesterday,and it idles smooth as a baby's bottom now.

The issue that remains is that there is some kind of mild stumbling around 1500rmps under load. Feels like one cyclindar coming up short, not a complete miss. I'm suspicious that this mechanic inserted the synch a tooth retarded. Just reminds me of how cars ran when spark advance was retarded too much in the olde days. At higher rpms it runs fine (though still lacks that certain aggressive edge I expect at higher rpms.)

4.0 /6 (not ohc); new wires, plugs; cleaned MAF, IAC; no vac leaks I can find now that the EGR thing is cleaned up. Fuel pressure tested right. Any way to test the sync position without removing it??
 
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