Lean idle mixture only in drive.

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Clone TIE Pilot

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Aug 14, 2011
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I have a weird idle issue with my L69 305. In park I can easily set the air fuel solenoid dwell to 30 degrees in park. However, most instructions state to set the mixture solenoid dwell in drive in which the computer is stuck in rich mode offsetting a lean mixture., Again in park the dwell varies and hovers around 30 degrees like it should but s steady at 8 degrees in drive. The curb idle in drive is set at 600 rpm and the engine does have a stable smooth idle despite the steady rich command. I have the needle mixture screws turned 4 1/2 turns out and using the IAB valve to fine tune the idle mixture.

I would think a vacuum leak would affect idle both in drive and park and prevent getting a proper dwell reading in either gear. Could it be a fuel flow issue? Currently I have a dead head pressure regulator installed between the stock return style fuel pump and the carb set to 7 psi. Cliff Ruggles says Qjets can take 8 psi and the factory repair manuals say different fuel pressures ranging from 7 to 9 psi depending which manual you read. Higher fuel pressures do seem to rasie the mixture solenoid dwell, (leaner command).
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,848
2,591
113
Galaxy far far away
Bump.

Other thing I think it could be is an false lean reading caused by an exhaust leak. I replaced the head to header gaskets but had to loosen the pipe flanges to do so. With the old TES headers the O2 sensor bung is close to the doughnut pipe flange. Possible its getting a false lean reading due to an exhaust leak and reversion? https://gbodyforum.com/threads/exhaust-doughnuts.85722/#post-911863
 
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