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High Idle and P0300 code


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My 2003 STS has an intermittent high Idlle (3000) RPM which happens while i am driving and sometimes when starting the car the idle is very low (300). I also have a mis-fire on #6. I checked the plug and it looked OK and replaced it anyways. Before i spend $70 on the injector, is there a way to test it? To replace the injector i need to relieve the pressure, can i just do this with a towel or do i need to buy a $200 pressure Gauge assembly. All suggestions appreciated

Dan

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P0300 is an intermittent miss. I would start by checking the wires and plugs, make sure your plug boots are fully seated and if you have close to or do have 100000 miles on your STS you need to change your plugs.

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You can check the injector by listening to it with a stethoscope. It should have the same rhythmic ticking as the others do, but injectors are pretty reliable. I doubt that's your problem. The 2000+ engines do not have plug wires. It could be a bad coil in the ignition cassette (if the plugs are good), but you might want to check for a ripped plenum and clean the TB first.

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You can check the injector by listening to it with a stethoscope. It should have the same rhythmic ticking as the others do, but injectors are pretty reliable. I doubt that's your problem. The 2000+ engines do not have plug wires. It could be a bad coil in the ignition cassette (if the plugs are good), but you might want to check for a ripped plenum and clean the TB first.

Thanks Ranger, I'm going to try replacing the coil and boots. the parts guy at cadillac said he hadn't sold an injector in a long time, which ,made me wonder about the injector. Buying from Rock auto, great pricing. Will check the plenum and all the air/vaccum lines. cleaned the throotle body and it was a a pain getting the air filter box back together, maybe an air leak there.

Dan

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You can check the injector by listening to it with a stethoscope. It should have the same rhythmic ticking as the others do, but injectors are pretty reliable. I doubt that's your problem. The 2000+ engines do not have plug wires. It could be a bad coil in the ignition cassette (if the plugs are good), but you might want to check for a ripped plenum and clean the TB first.

Thanks Ranger, I'm going to try replacing the coil and boots. the parts guy at cadillac said he hadn't sold an injector in a long time, which ,made me wonder about the injector. Buying from Rock auto, great pricing. Will check the plenum and all the air/vaccum lines. cleaned the throotle body and it was a a pain getting the air filter box back together, maybe an air leak there.

this morning i got a misfire on 7, now i have a P0300 random misfire multiple injectors. 6 original misfire is on the front coil and 7 is on the back coil. can something else be causing this?

Dan

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Did you do something in between this morning and yesterday when you were just getting #6 misfire? What about your plugs, did you replace them? It sounds like you might not have something back together tight that you took apart yesterday.

Edited by heitzman
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Just reread your last post. Hard to imagine 2 coils going out at the same time. I'd check that plenum real good since it is now affecting both banks. No lean fuel trim codes?

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Just reread your last post. Hard to imagine 2 coils going out at the same time. I'd check that plenum real good since it is now affecting both banks. No lean fuel trim codes?

Dan

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when i went to screw around with the plenum i found that i never tightened it to the throttle body after cleaning it, duh. i also replaced the coil, plugs and rubber plugs and she is running great. thank you everyone for your help and advice, i very much appreciated your help.

Dan

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Did you do something in between this morning and yesterday when you were just getting #6 misfire? What about your plugs, did you replace them? It sounds like you might not have something back together tight that you took apart yesterday.

I thought it might be something loose. Good luck with your Caddy

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