Rough idle and low speed chug
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Northstar Engines and System Technical Discussion Discussion, Rough idle and low speed chug in Cadillac Engine Technical Discussion; I have a 03 SLS. I have recently aquired a rough idle. I have received these codes. PO300,PO171,PO174,P1360. I have ...
  1. #1
    Daddywheats is offline Cadillac Owners Member
    Automobile(s): 2003 sls
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    Rough idle and low speed chug

    I have a 03 SLS. I have recently aquired a rough idle. I have received these codes. PO300,PO171,PO174,P1360. I have cleaned the maf sensorand checked connections. Really frustrated. Anyone have this problem too?

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, install a sound system
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    Re: Rough idle and low speed chug

    The P0300, 0171, and 0174 codes generally point to a vacuum leak with attendant miss.

    Remove the engine beauty cover and start the car. Squirt a shot of carb/choke cleaner or starter fluid at the base of the plenum - that rubber connector between the throttlebody and intake manifold - there's a hose clamp screw down in there - that's where to shoot. Any idle speed change ??? New plenum, $40, dealer part only. (#2 in the manifold diagram.)

    Otherwise, go through every vacuum line off the throttlebody to about 3 various sensors/valves. Look for cracked plastic pipes or rotted rubber connectors. Any can be replaced by a proper sizes length of blister-pack vacuum hose from any parts house. Also check the EVAP solenoid/vacuum connector sticking out the back side (driver's side) of the throttlebody. Vacuum there, too.

    The PCV system uses a fixed orifice in the rear cam cover, passenger side. Check that pipe and the corresponding PCV fresh air feed in the front cam cover.

    Listen carefully at the p/s pump end of the intake manifold: there's a manifold overpressure valve (blowoff) in the intake manifold cavity that sometimes develops a leak. (It's in where the hand is lifting the manifold.)

    Is the oil fill cap properly seated and tightened ? a vacuum leak there (!) will set codes. Believe it.........

    For the P1360 (Ignition coil group 2 circuit) try disconnecting each ICM connector (in the 2 coil pack legs) and clean the multi-pin connectors with Radio Shack Tuner Cleaner spray. Smear a tad of vaseline around the connector seal ring upon assembly.

  4. #3
    Daddywheats is offline Cadillac Owners Member
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    Re: Rough idle and low speed chug

    Plenum it is. I love this forum. Thanks for the help. Love that even with all the computers and such these days we are still able to work on these ourselves.

  5. #4
    Submariner409's Avatar
    Submariner409 is offline If it won't run, install a sound system
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    Re: Rough idle and low speed chug

    OK - go to a NAPA store and get a fuel line quick-disconnect kit. Not expensive. You'll need it for the fuel rail right next to the throttlebody. P/U an intake manifold gasket set at the same time. Keep track of all the O-rings on the fuel injector tips - lube them with a drop of oil when you seat the injectors again. Might as well clean out the throttlebody while you're in there - throttlebody cleaner, a toothbrush, and rags. Get the idle air passage holes, too. Fuzzy pipe cleaners - craft/hobby shop. Don't sweat the inside of the manifold - it will probably be an oily mess - PCV vapor flow - and you can't get to all the nooks and crannies, so let well enough alone. The intake manifold bolts only use 5.5 ft/lb or 89 in/lb of torque - not much, but too much and the composition material cracks at the bolt flanges. Do clean off the overpressure valve flange, but use mineral spirits only - exotic solvents eat the flange seal ring.

    3 beers and a sore back. Magic words help.

  6. #5
    kckranz's Avatar
    kckranz is offline Cadillac Owners Fanatic
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    Re: Rough idle and low speed chug

    Quote Originally Posted by submariner409 View Post
    OK - go to a NAPA store and get a fuel line quick-disconnect kit. Not expensive. You'll need it for the fuel rail right next to the throttlebody. P/U an intake manifold gasket set at the same time. Keep track of all the O-rings on the fuel injector tips - lube them with a drop of oil when you seat the injectors again. Might as well clean out the throttlebody while you're in there - throttlebody cleaner, a toothbrush, and rags. Get the idle air passage holes, too. Fuzzy pipe cleaners - craft/hobby shop. Don't sweat the inside of the manifold - it will probably be an oily mess - PCV vapor flow - and you can't get to all the nooks and crannies, so let well enough alone. The intake manifold bolts only use 5.5 ft/lb or 89 in/lb of torque - not much, but too much and the composition material cracks at the bolt flanges. Do clean off the overpressure valve flange, but use mineral spirits only - exotic solvents eat the flange seal ring.

    3 beers and a sore back. Magic words help.
    Sub - Previous post - general engine layout photo - how'd you get all those sponsors to endorse your strut tower brace?

  7. #6
    Submariner409's Avatar
    Submariner409 is offline If it won't run, install a sound system
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    Re: Rough idle and low speed chug

    Each one of those stickers is good for 5 hp at redline. I learned that from the CTS and Honda threads.

    (The CORSA and Pennzoil are legit - my grandson stuck the others on.)


  8. #7
    Mark C's Avatar
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    Re: Rough idle and low speed chug

    Actually who makes that strut, and did it make a difference that you could tell on the cars handling? I don't have one on my 2000 STS and I don't think one from a 97 or prior will fit without reworking the section over the master cylinder and maybe the width.

  9. #8
    Submariner409's Avatar
    Submariner409 is offline If it won't run, install a sound system
    Automobile(s): 2002.5 F55 STS/65500mi, 2004 Ford F150 SuperCab4x4
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    Re: Rough idle and low speed chug

    GM/Cadillac makes the strut tower brace. It was stock on 2000-2003.5 Japanese export Sevilles. Special order at a GM dealer. P/N 25653157. $40 +/-

    The only time you'll notice a difference is during a back country road OMG !!! screamer run. Otherwise, bling. The 15mm strut tower bolts use 33ft/lb of torque - use 1 drop of Locktite red on the tip of each bolt on assembly - don't loosen the 3rd bolt. Not necessary.

  10. #9
    Mark C's Avatar
    Mark C is offline Cadillac Owners Connoisseur
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    Re: Rough idle and low speed chug

    45.81 shipped out of gmpartsdirect.com.

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