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idle issues on 945 NA - what am I missing? 900 1993

Car is a 1993 945 NA w/ Regina, 116K.

Once cold weather was upon us about 2 months ago, I started having idle problems. It's at its worst when the car and the ambient temperature are both cold. The motor shakes and shimmies like it's on three cylinders, and the idle see-saws between about 600 and 1200, like the car is going to die and the computer yanks it back from the abyss every other second. Idle is significantly better once warmed up (or in warmer weather), but still not smooth.

things I've done recently (not necessarily aiming to cure this issue), in no particular order:
-replaced spark plugs
-replaced FPR
-replaced o2 sensor
-replaced RSR
-cleaned flame trap
-Cleaned throttle
-cleaned engine grounds
-cleaned IAC, swapped out with other cleaned ones, no improvement
-swapped out injectors for a freshly-cleaned set and installed with new seals
-replaced a bunch of the vacuum lines (manifold to MAP sensor, manifold to FPR, manifold to flame trap, manifold to black and white check valve behind engine)
-shock-cleaned the top end with water followed by seafoam stuff as per FAQ (car runs noticeably smoother, but idle unaffected)
-confirmed fuel and spark at all cylinders
-confirmed vacuum ports on manifold are not plugged with crap

FYI:
-MAP sensor and air temp sensor were replaced with new last summer, so they should be okay. Air box thermostat is jammed onto fresh air setting. Recent gas mileage is not great, about 19 MPG.

additional known problem:
exhaust leak where manifold meets downpipe. I bought studs, nuts, and gasket at the dealer today, but that's not a project I'm looking forward to. Would an exhaust leak cause the o2 sensor to get an inaccurate enough reading to throw the mixture way off? I expect the leak is newer than my idle issue anyway, since the car passed VA inspection early this month, and the leak is quite audible, so I'd be surprised if they'd missed it.

I have blown through 2 cans of carb cleaner trying to find a vacuum leak. I'm considering removing the intake manifold and reinstalling with new gasket just on the off chance that there's a leak I couldn't detect. I have poor hearing, and with the exhaust leak noise, I have not tried the stethoscope method to ID any leaks.

I have a fresh set of plug wires which I will install tomorrow. I have contemplated new dist cap and rotor, but cap appeared brand new when I bought the car a year ago (nice and clean, unlike rest of engine compartment).

Anyone have any thoughts on where to go from here?

thanks,
John

 





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New idle issues on 945 NA - what am I missing? [900][1993]
posted by  dinomartino  on Wed Dec 31 11:04 CST 2008 >

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