Is it common for higher mileage FC's to have misfires? Say 150k and above? My 87 GXL seems to have an unsteady idle. Put some lower octane gas in and it seems to have made it a little bit steadier. I don't know if that's good for it or not. Buddy tells me it might be a vacuum leak to cause the idle fluctuation.

 

Missing is something I have not figured out yet. Most likely the culprit is something internally, like coolant leaking into the combustion chamber, at least thats what I think the case is with mine. A fluctuating idle is always a vacuum leak, any air that is entering the system that is unmetered will cause that.

 

Any common areas of vacuum lines I need to check out first? Maybe a vacuum print-out on MotorAllData would help right?

 

common leak is from everywhere, under the intake manifold there are a bunch of lines which break very easy, just get some carb cleaner and start spraying hoses and manifolds but dont start a fire, have you treid replacing plugs and wires and always run low octane on FC's higher octane doesnt really help on the NA's

 

low octane on NA FC's

high on Turbo FC's

 

Oh I see. Yes, I recently did a tune-up on it before I smogged the car. Didn't notice a difference though. That was about 1200 miles ago. basically I have to check all the lines for leaks right ? Do the coils have any effect on the idle?

 

I would think only missing, but the coils usually never check out bad. Timing defenitly has a huge impact on idle.

 

On a 87, just go to your variable resistor, and with the engine fully warmed up, advance the screw towards the RICH setting (Clockwise). The screw only has a 3/4 turn to it. Do not turn/force your way past the stops on each end.

The car will idle without the *missing* your describing. It ain't the plugs/wires/coils.