Hard Shifting Problem 98 STS
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Northstar Engines and System Technical Discussion Discussion, Hard Shifting Problem 98 STS in Cadillac Engine Technical Discussion; Hey, i have a 98 STS with 110k miles. There is a hard shifting problem. It starts off really bad ...
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    akaz87 is offline Cadillac Owners Fanatic
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    Hard Shifting Problem 98 STS

    Hey, i have a 98 STS with 110k miles. There is a hard shifting problem. It starts off really bad when its cold, then it gets better. It still isnt right. Its pretty hard actually. This has been happening since I had the car. I also have a hard idle I cant fix, can these be realated, no codes. The shifting isnt a problm, itts just when you put the car in gear, it kind of goes bang.

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    STS 310 is offline Cadillac Owners Connoisseur
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    Re: Hard Shifting Problem 98 STS

    Quote Originally Posted by akaz87
    Hey, i have a 98 STS with 110k miles. There is a hard shifting problem. It starts off really bad when its cold, then it gets better. It still isnt right. Its pretty hard actually. This has been happening since I had the car. I also have a hard idle I cant fix, can these be realated, no codes. The shifting isnt a problm, itts just when you put the car in gear, it kind of goes bang.
    Perhaps its time for a tranny service. New Filter and Fluid. Has it ever been serviced? If not, may be time. Funny what a clogged filter and burnt or worn out fluid will have on performance

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    Re: Hard Shifting Problem 98 STS

    Quote Originally Posted by akaz87
    Hey, i have a 98 STS with 110k miles. There is a hard shifting problem. It starts off really bad when its cold, then it gets better. It still isnt right. Its pretty hard actually. This has been happening since I had the car. I also have a hard idle I cant fix, can these be realated, no codes. The shifting isnt a problm, itts just when you put the car in gear, it kind of goes bang.
    What is a "hard idle"....??? Fast idle...??? Rough idle...??? possibly that is what is causing the trans shift quality problems on the garage shifts from park to neutral. If the engine is idling too fast then the system will deliberately "bang" the trans into gear to protect it. Hard shifts are easier on the trans than soft ones.... Could be a vaccum leak at the manifold seals....or a sticking throttle blade or IAC.

    I would start by cleaning the throttle body to make sure the throttle blade is not hanging on some deposits. Hold the throttle blade wide open with the engine off and spray the throttle body bore with carb cleaner and scrub with an old tooth brush...also clean the backside of the throttle blade. Get the desposits off the ID of the throttle bore and blade backside so that the system can control the idle correctly. Disconnect the negative battery cable for 30 seconds when you do this to reset the idle learn offsets for immediate response to the cleaning process.

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    akaz87 is offline Cadillac Owners Fanatic
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    Re: Hard Shifting Problem 98 STS

    The idle is rough. When you sit a a stop light you feel a roughness in your feet. Its not high. I have clnead the throttle body and it didnt seem to help any. As for a leak i'm not sure. How can I test this? I tired the WD40 over to see if it sucks any in and I didnt seem to get anything. Thanks for your posts. Is a tras. job expencive to have done?

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    Re: Hard Shifting Problem 98 STS

    Quote Originally Posted by akaz87
    The idle is rough. When you sit a a stop light you feel a roughness in your feet. Its not high. I have clnead the throttle body and it didnt seem to help any. As for a leak i'm not sure. How can I test this? I tired the WD40 over to see if it sucks any in and I didnt seem to get anything. Thanks for your posts. Is a tras. job expencive to have done?
    Odd that the idle would be rough without a SES light...the onboard diagnostics has a cylinder mis-fire diagnostic that is pretty good at catching a miss....

    Have you looked at the fuel pressure regulator or looked at injectors to see if one is leaking at idle....

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    akaz87 is offline Cadillac Owners Fanatic
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    Re: Hard Shifting Problem 98 STS

    Yea no SES light, I though that was weird also. I have replaced the FPR which fixed my hard start problem. The injectors dont leak, I put 50 lbs of pressure on them with no leak. I dont get it.

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    Re: Hard Shifting Problem 98 STS

    Are you sure the rought idle isn't just the normal idle for a 98 STS and that there isn't a broken engine/trans mount that is causing the clunk into gear..???

    98 STS's were known for a bit of a tremble at idle...the idle was not dead smooth and you could feel a bit of roughness in a lot of the cars. The idle isolation was not quite as good with the engine mount system in the 98 STS and with the higher output engine (300 HP L37) and the more radical cam timing the engine did idle a little rougher. If there is a broken engine/trans mount it would exacerbate this roughness and cause a clunk into gear that could be perceived as a rough or harsh shift.

    Open the hood and start the engine. Put it in drive and load the engine against the trans by holding the brake firmly and watch the engine motion. It will move some as the engine is loaded but the movement should be relatively small and smooth and controlled...no sudden jerks or clunks. Try it in drive and reverse to see if there is an obviuos problem with a mount.

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