i have a 2000 saturn sl1. i have codes p0301 and p0507. not sure what the poroblem is, i changed plugs,wires, coils the iac , tps and oxygen sensor#1, i have misfire cylinder#1 and still back firing a little it runs ok better have high idle still ,been high every since i bought 3years ago, what could be doing this , injector or cat. i sprayed cleaner all around the motor instuff nothing, thanks...

 

The codes 301 is 1 cyl misfire - 507 AIC (air idle control) rpm higher than normal. When slowing down to a stop light try putting the trans in neutral, and see if the tach shows the rpm's running to high. There are two things that can make that occur the TPS (throttle position sensor) which is located on the throttle body right above the AIC. I have a 2001 SL I just bought a month ago and I had a runaway idle problem. It would idle around 1800 rpms, I always put the car in neutral when waiting at a traffic light, so found the problem right away. Another thing I changed was the CPS crankshaft position sensor. Which can cause a higher than normal idle. The higher the idle the more wear and tear your putting on your transmission.

 

Another problem is that with idle being at 1800 makes stopping the car that much harder.

 

did you try spraying around the intake manifold near #1?

 

Sounds similar to what my 2001 L300 was doing. Replaced the Camshaft sensor and all was well... altho mine would also occasionally die and not start. That was a few years ago.

 

sorry no cam sensors in an S car

 

thanks i have not done the cps. my 2000 sl1 still has misfire cylinder1 and high idle i also did egr .car runs pretty good,i have no ideal what this could be

 

If your co2 sensors go bad, the engine will not get the proper fuel mixture and can cause a misfire. The coil could be bad too, or old plug wires. Have a garage scan the car, they usually show the problem.

 

Have you tried this yet?

The garage already scanned the codes which you posted in your original positing so I'm not sure why he suggested it again....(?)

There are no CO2 sensors on the car -- I think he meant he meant O2. While they affect the air/fuel mix, it's unlikely that it would lead to a repetitive misfire in only a single cylinder.

The misfire with high idle together point at the likelihood of an intake manifold gasket leak at cyl1 -- that's why i suggested you spray around it with throttle body cleaner (cool engine please) to see if the rpms change...........if they do you've found your leak