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Trying to improve rough idle. experiment

 
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  #1 (permalink)  
Old 10 Feb 2012, 08:25 pm
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Default Trying to improve rough idle. experiment

Ok details first. i have an 04 PT non turbo 205,000+ and have been running high octane shell gas in it all week. just got car so this was first tank of gas.

Second fill up i added Lucas gas treament and used 87 octane gas at walmart or murphy usa whichever you call it. I really almost had to break my arm to push that 87 button.

Within 20 miles i now have a check engine light with code P0420 Catalyst 1/1 efficiency below required level P0420 Error Code Information (link posted in another thread by cruizer). I was also driving with a lot of rain and this is the first we have driven it in heavy rain.

Any suggestions? Is this common for using lucas gas treament. Should i disconnect battery so computer can relearn.

Other plans for next week, clean IAC, Check plugs and wires, check for vacuum leaks.

Thanks for any help and i plan to update with each new thing i do.

Last edited by rhinocruiser; 10 Feb 2012 at 11:07 pm. Reason: added link to error code info page
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Old 10 Feb 2012, 09:05 pm
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Default Re: Trying to improve rough idle. experiment

well, for starters, high octane gas is useless in non-turbos. i believe it actually hinders mileage and performance and qute possibly might be the cause of your dilemma.
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Old 10 Feb 2012, 09:12 pm
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Default Re: Trying to improve rough idle. experiment

soyomb -thanks for reply - you might be right but i ran all week with high octane without a hitch and just now got 87 and had a check enginelight. I usually only risk 87 at quality gas stations but figured i would try it because i was using lucas gas treatment.

I also wanted to mention i understand that a little over 20 miles is not a good test to see if i have improvement and the check engine light could have happened regardless but it still seems strange. Maybe it is just knocking some gunk loose and making the code appear.
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Old 13 Feb 2012, 09:38 am
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Default Re: Trying to improve rough idle. experiment

Ok 70 miles in on a fresh tank of 87 from walmart and lucas treatment; the check engine light goes out. Drove 20 miles with no light; next day started car; check engine light back on, and drove 35 or so miles. Check engine light back on and now throwing P0300 code (MULTIPLE CYLINDER
MISFIRE) and still P0420. I was really wanting to try to make it through a whole tank but i think i might syphon gas out and retry lucas with 87 from shell to see if anything changes.
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Old 13 Feb 2012, 10:14 am
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Default Re: Trying to improve rough idle. experiment

Quite a few items can contribute to these issues - things like water in your fuel, poor fuel flow, carbon buildup on the spark plugs, crappy plug wires, bad plugs, failing coil, etc.

My first suggestion would be to run a bottle of Stabil through it. If you have a Shell gas station, fill up a bit past half way on your tank with their 91 octane fuel. It is gas with some of the least amount of ethanol out there. Less than 1%. You want to run non-ethanol in your tank while you run Stabil, to allow it to better rid your tank of any water, white rust, ethanol, etc.

After you've run your tank down to about a quarter, fill up with good 87 octane and add a full can of Seafoam. These two together will help clean up your tank a bit. I'd also pull the plugs and make sure you've not got carbon buildup/deposits. Run your tank with Seafoam, but never allow your tank to get below one quarter. With all that mileage, I'm willing to be the previous owner let that car sit for a while, and that's when you start getting crap in your tank. Personally, I'd run my tank down to just below a quarter then drain the thing. Sounds to me like you're carrying a load of crud in your tank.

Add to this, it's very difficult to change the fuel filter as it's part of the pump assembly which is embedded inside your tank. If you aren't successful with the Stabil and Seafoam trick, and you try draining your tank and still having issues, the last suggestion is to pull the pump and replace it completely. It's definitely a PITA to do.

Make sure you check your plugs and wires!
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Old 13 Feb 2012, 10:21 am
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Default Re: Trying to improve rough idle. experiment

Quote:
Originally Posted by soyomb View Post
well, for starters, high octane gas is useless in non-turbos. i believe it actually hinders mileage and performance and qute possibly might be the cause of your dilemma.
The only issue with running high octane fuel in normally aspirated engines is the amount of ethanol and other crud in it. High octane fuel generally runs 10% to 15% ethanol. I'm always searching for places with less ethanol as even though it's a performance enhancer, it's hard on seals and lines. Really it shouldn't hinder the performance of an NA engine.

Here's the dillyo - if you've run 87 all the time, you've got your engine trained to run on reduced amounts of ethanol, which affects your F/A ratios. Also, 87 is a heavier mix of fuel, and additives and crud in 87 tend to sink quite rapidly in your tank, meaning they hit the bottom and less of the crud actually runs through your system. The down side of that is if your vehicle sits for long, that crud really does settle in, then you flush some 91 and up octane fuel with ethanol in it, it's like turning on a washing machine - all that crud gets kicked up off the bottom of the tank and starts flowing into the system.

Sounds silly, but this happens quite often. Run lower octane fuel for a long time, then dump in some high octane, all of a sudden you start having performance problems.
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Old 26 Feb 2012, 07:55 pm
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Default Re: Trying to improve rough idle. experiment

Thanks for all that info chromenut that is some real crazy stuff with the ethanol gas. I will definitely use the can of seafoam and stabil as i think you are right about the car sitting for some time.

Onto the experiment. Still idling rough

The PT is now been on a strict diet of shell 87 gas and withiin a couple fill ups the check engine light is gone and no codes present. Lucas gas treatment was not used again with any fill ups. I plan on trying the Lucas again with the shell gas now that everything is stabilized.

I have pulled out the IAC valve and cleaned it as good as possible with carb cleaner. It had some hardened gunk on the edges of the black piece in there which i could see as being a problem for proper airflow. I also cleaned as much as i could inside the chamber where the iac valve sits. I did not have a chance to test it to see if anything moved but i will next time i pull it out.

On inspection of the brakes i noticed the lower motor mount is bad and will replace it as soon as possible and might try the suggestion of using urethane to fill gaps.

Conclusion so far: idle still rough and shell 87 seems to work great with no errors.

chromenut what would be the best process of draining the tank? Would a syphon house or pump be best or is their an easy way to do it on the tank. I have dropped gas tanks from other cars but dont think i ever saw an easy way to drain tank.
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Old 26 Feb 2012, 09:21 pm
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Default Re: Trying to improve rough idle. experiment

Driving it empty's the tank
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Old 26 Feb 2012, 10:16 pm
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Default Re: Trying to improve rough idle. experiment

We use our local gas house and there one of the few that sells under 10% ethanol around here. Wifes 06' NA started skipping a little and slight miss. Thats when i found out she had been saving a few pennys and buying gas from walmart/murphys last couple of weeks before this started.

Got a bottle of the black fuel injection cleaner (cant remember the brand but have used it in the past with excellent results) and filled up with the gas house fuel. It now runs smooth again and she dont use there gas anymore either.

A lot of locals have had problems with their fuel as well so dont know if its everywhere or just local but why chance it just to save a few pennies?
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Old 28 Feb 2012, 07:16 pm
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Default Re: Trying to improve rough idle. experiment

thanks xwing777 i think i have seen the same results with using walmart gas and have shifted to shell.

uptownsport: yes this should be the easiest way to get everything from the tank into the fuel system

I just checked the iac valve to see if it is working and the black part is moving back and forth. Not sure if it working correctly but it is working and this was also the only part i saw moving on it. After testing this the engine revved quite a bit and now has p2074 code which i saw in another post in air related so i will rule it out for now and expect it to dissappear soon.
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