1998 S1 runs sluggish and rough after full warmup, but only intermittantly

[Mgtaylor]

This Saturn S1 (1998) runs good most of the time but will after running for
a good long time will sometimes begin chugg1ng and running rough. There is
a trouble code in the computer for coolant sensor, but of course the car
does not misbehave like this whenever the mechanic has been looking at it!
Due to previous idling problems, which were fixed, the CPS. MAP, Throttle
speed and Idle speeds sensors have been changed over a period of time this
summer. This rough running seems to be a new problem. Sometime it will
run rough for a few minutes and then clear up, sometimes it continues
until the car is shut down and cooled off for a while. The fuel pump
pressure is at 45-50 lbs - could this be the problem? Thanks in advance
for any replies to this.

 

[Bob Shuman]

What are you waiting for? Replace the Coolant Temperature Sensor. Sounds
like it is intermittently reporting a cold engine so you are getting too
much fuel and it runs rough. These are known to fail often and are cheap
and easy to fix.

Bob

 

[Mgtaylor]

Thank you for your answer Bob. The coolant sensor code is gone and now I
have a P0301 - missing on cylinder #1. This code only shows up when it is
actually malfunctioning (random) which is why the mechanic has not seen it.
According to the manual there can be a whole plethora of causes for this
including spark plug, plug wire, low fuel output at injector(s), coil,
emissions components, ignition weak or vacuum leak.

There are no other trouble codes so far. Could low fuel output cause this
only in cylinder #1 because #1 is at the farthest point of the injector
assembly from the fuel input?

 

[Bob Shuman]

I'd guess you have a dirty connector on the fuel injector or a bad wire or
plug. You can use some electronic contact cleaner to clean the connector
and then see if it comes back. I'd also take a look at the ignition coil
tower and all spark plug connections there too. They get corroded and can
short out. You can easily remove and clean this off to remove the
corrosion/growth. Could also be a head gasket leak, but I would not jump
to that conclusion just yet.

Good luck.

Bob