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Rough Idle need help (Chevy)


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I have a 1988 iroc (donar car) with the L03 engine 305 TBI that runs rough after it goes into closed loop. I hooked my snap-on scanner on it and found a weird reading I see 8-10" Hg at Idle and up to 22"Hg at part throttle at the MAP sensor doesn't this sound backwards?? when I try to pull a hill the ECU "sees" no load(ie: high vacuume) and leans the mix that turns on the knock sensor and retards the timing and it bucks and has little power. All other lines on the scanner look normal I think the vac signal to the MAP may be inncorrect but I dont have a diagram to go by and the haynes manual was of no help!! Keith

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Are your vacuum numbers just at the MAP sensor? I think you have a vacuum leak, however. The 22" at part throttle is quite believable, but the 8-10 at idle is wrong. The pressure reading at the MAP should equal the engine vac at all rpms. idle should be close to 18" if not higher, part throttle can vary widely between 5 and 25 depending and WOT should be zero.

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