Thread: rough idle

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  1. #1 rough idle 
    GTP Level Member 04lss's Avatar
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    The idle on my GTP is getting worse. I did the spray brake cleaner around the SC to check for vacuum leaks with no change in idle. No Missfire codes, no sensor error codes. I cleaned my MAF with maf cleaner.
    The fuel system is operating in closed loop and my LTFT is 16.4 (seems high). Im not sure what to check next. It does have a camshaft position sensor code. (from what ive read it doesnt affect Idle but Im not sure.)
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  2. #2 Re: rough idle 
    GTP Level Member 04lss's Avatar
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    It seems to be getting reasonable mpg as well 25 average, and do have fun with it.
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  3. #3 Re: rough idle 
    Turbo is the way to go. Fivefingerdeathpunch's Avatar
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    16.4 on the trims means vacuum leak.

    Time to smoke test it.

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  4. #4 Re: rough idle 
    GTP Level Member 04lss's Avatar
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    Quote Originally Posted by Fivefingerdeathpunch View Post
    16.4 on the trims means vacuum leak.

    Time to smoke test it.
    I unplugged the MAF and it ran WAY better once it got warmed, I might just replace it, and all the vacuum hoses.
    how does the smoke test work?
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  5. #5 Re: rough idle 
    Turbo is the way to go. Fivefingerdeathpunch's Avatar
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    If it ran better unplugged, then it could be the whole issue.

    But a smoke test fill all the vacuum hoses and whole motor with smoke and if any comes out of spaces that would suck in air like a gasket or vacuum line, then you know you have a leak.

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  6. #6 Re: rough idle 
    GTP Level Member 04lss's Avatar
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    Quote Originally Posted by Fivefingerdeathpunch View Post
    If it ran better unplugged, then it could be the whole issue.

    But a smoke test fill all the vacuum hoses and whole motor with smoke and if any comes out of spaces that would suck in air like a gasket or vacuum line, then you know you have a leak.
    how would i do a smoke test. i dont have anything that can make smoke like that?

    I also have a 165 tstat, that i am pretty sure was never tuned for (i know the motor richens the fuel trim when in warm up. IDK if this shows up on the LTFT. My monte had an abnormally high LTFT as well, i wonder if its something environmental
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  7. #7 Re: rough idle 
    Bastard Reptile's Avatar
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    The thermostat won't make the idle worse.

    I vote MAF as well.
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  8. #8 Re: rough idle 
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    It does soung like the maf. but since all of us love to replace lim gaskets spray some cleaner around it too
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  9. #9 Re: rough idle 
    GTP Level Member 04lss's Avatar
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    Quote Originally Posted by Reptile View Post
    The thermostat won't make the idle worse.

    I vote MAF as well.

    i realize it wont affect the idle, but since it richens the fuel mix ( i remember seeing this from the fuel vs temp tables in my monte) I was thinking it might explain the LTFT
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  10. #10 Re: rough idle 
    GTP Level Member 231FUN's Avatar
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    If it was my car I'd throw at least a 180 or a stock tstat in it at this time of the year, then I'd find the vac leak.
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  11. #11 Re: rough idle 
    GTP Level Member tomtom123's Avatar
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    To smoke test you dump half a bottle of sea foam slowly into the break booster line.
    As it idles it should smoke anywhere there are leaks. Then the rest of the sea foam you can dump into the fuel tank. At least thats what I did. It's supposed to help kinda clean out the injectors and what not a bit
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  12. #12 Re: rough idle 
    Killa Bee Scottydoggs's Avatar
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    thats not a smoke test, sheeesh. you can find a exhaust leak that way. not a vac leak.


    smoke test is when smoke is pumped into a vac line. if theres a vac leak smoke will leak from the broken line or gasket area.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  13. #13 Re: rough idle 
    GTP Level Member tomtom123's Avatar
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    That's not a smoke test? Doesn't the break booster connect to the vacuum lines? That's what I was told.
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  14. #14 Re: rough idle 
    Killa Bee Scottydoggs's Avatar
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    vacuum lines suck in, how will seafoam make a vac line show a leak? all the smoke goes out the tail pipes.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  15. #15 Re: rough idle 
    GTP Level Member tomtom123's Avatar
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    Makes sense when it's said that way. Where were you when I was told to do what I did? =P
    The process I was told to do was.

    Pour half a bottle slowly into the line I showed in the pic while running. Once half a bottle has been put in, shut the car off for 30 mins and see if smoke comes out anywhere. Run the car for a bit and drive down the road for a while until it's done smoking.

    Hmm.
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  16. #16 Re: rough idle 
    Killa Bee Scottydoggs's Avatar
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    hmmmmmmmm is right lol.


    to check for vac leaks other then a smoke test, car at idle you can spray carb cleaner at the vac lines, intake manifold gaskets, tb gasket, sensors with vac lines to them. injectors. aka the whole top of the engine.

    if the idle jumps up, you found a leak area.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  17. #17 Re: rough idle 
    GTP Level Member tomtom123's Avatar
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    Yeah, I've done that before but with no results. Did it a few times because my ltfts are always like -22 while cruising down the road, bouncy between like +3 to +10 at idle and it idles poopy. But I was told the ltfts problem is because of the cam since I cammed the car. But I checked multiple times for vacuum leaks and no results yet
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  18. #18 Re: rough idle 
    Bastard Reptile's Avatar
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    Quote Originally Posted by tomtom123 View Post
    Makes sense when it's said that way. Where were you when I was told to do what I did? =P
    The process I was told to do was.

    Pour half a bottle slowly into the line I showed in the pic while running. Once half a bottle has been put in, shut the car off for 30 mins and see if smoke comes out anywhere. Run the car for a bit and drive down the road for a while until it's done smoking.

    Hmm.
    That's a top engine clean.

    aka. Fogging the mosquitoes.
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