slight miss at idle

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Ive been getting inconsistent fuel mileage in the saturn and exhaust pop at idle fairly often was tuned up 2000 miles ago. Wires tested good, coils are good, no cel. Intake gasket and vac lines are good. O2 sensor seems to be switching pretty good. I cleaned the throttle body no change. Spark plugs looks good to. Egr is clean to. I drive the same route everyday and last time I got 36mpg this time 31..... same station and pump to. What else toncheck
 
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Originally Posted By: brandini
Winter gas?


ehh that wouldnt cause the little miss at idle though. And the gas mileage varies from tank to tank. It was 32 then 36 now 31 and this tank is right around 29.its getting worse,
 
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Engine has been very well maintained. And runs good while drivimg.
 
Even though I would have guessed a dirty throttle body I see you tried that. I'd get the exhaust analyzed and see what the readings are, might tell you a bunch. O2 sensors get lazy as they age.
 
Could be a dirty injector. I've had luck with Chevron Techron in the fuel. Believe it or not, MMO in the fuel might help too (but I did not say that)
smile.gif


However, as engines age, compression changes, valves don't seal as well, injectors don't spray as cleanly and so on. It all adds up to a slightly rough idle.
 
Originally Posted By: Cujet
Could be a dirty injector. I've had luck with Chevron Techron in the fuel. Believe it or not, MMO in the fuel might help too (but I did not say that)
smile.gif


However, as engines age, compression changes, valves don't seal as well, injectors don't spray as cleanly and so on. It all adds up to a slightly rough idle.


ngk copper plugs.
Its got 123,000 miles.
 
Originally Posted By: ram_man
Originally Posted By: Cujet
Could be a dirty injector. I've had luck with Chevron Techron in the fuel. Believe it or not, MMO in the fuel might help too (but I did not say that)
smile.gif


However, as engines age, compression changes, valves don't seal as well, injectors don't spray as cleanly and so on. It all adds up to a slightly rough idle.


ngk copper plugs.
Its got 123,000 miles.


Gapped at .040?
 
Many Saturns of that time had failure prone coolant temperature sensors. Sometime one sensor was connected to your gauges, and another one connected to your ECU. This could make you think that your sensors are fine when they aren't.

Such sensors aren't expensive, thankfully.
 
Originally Posted By: beast3300
Originally Posted By: ram_man
Originally Posted By: Cujet
Could be a dirty injector. I've had luck with Chevron Techron in the fuel. Believe it or not, MMO in the fuel might help too (but I did not say that)
smile.gif


However, as engines age, compression changes, valves don't seal as well, injectors don't spray as cleanly and so on. It all adds up to a slightly rough idle.


ngk copper plugs.
Its got 123,000 miles.


Gapped at .040?


Yes I believe that's what it is specd for. Double checked it
 
Originally Posted By: artificialist
Many Saturns of that time had failure prone coolant temperature sensors. Sometime one sensor was connected to your gauges, and another one connected to your ECU. This could make you think that your sensors are fine when they aren't.

Such sensors aren't expensive, thankfully.


mine has one ects. Its the metal sensor
 
Originally Posted By: 99Saturn
Ignition control module maybe. Probably some cheaper things to try first.


it has been replaced by the original owner. Not long before I bought it.
 
Although they are new, have you pulled the plugs to see if one is fouling or running lean from possibly a bad injector?
 
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Good thing I rechecked. They all look good and ran except that fourth plug it's solid black. So it's the fourth cylinder what do you guys think?
 
Did you start this up for less than 5 minutes before removing the spark plugs? If so then it's hard to tell for sure if cyl4 isn't burning all the fuel. Is this a SOHC or DOHC 1.9?
 
No it ran a good 20 mins before being parked for several hours . I pulled them out stone cold. And it's a sohc
 
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