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Registered
1999 STS
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9 Posts
Discussion Starter #1
So next on the long list of problems to deal with is the terrible shudder I have on the highway. It drives shudder free in town and highway till about 55 or 60 mph. Its is about a 3-4 second shudder then gone for 2 seconds then back for 3-4 seconds and so on and so on. I also have a sluggish acceleration and kickdown if this could be related. I was going to do plugs and wires next week to try to correct the acceleration issue but am getting no misfire codes.

Does this seem like an ignition issue or a torque converter issue?

Any ideas are appreciated. Thanks.
 

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Registered
1999 STS
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9 Posts
Discussion Starter #3
The codes I'm getting are:

C1285 - Lateral Accelerometer Sensor Circuit Malfunction
C1288 - Steering Sensor Circuit Malfunction
P0719 - Brake Switch Circuit Low Input
C1738 - Exhaust Solenoid Valve Short to GND
C1763 - Right Rear Position Sensor Input Fault

Also,
While the shudder is going on if I shift to neutral it does not go away. I spoke with my uncle (he's a tranny engineer at the proving grounds) and he told me to rule out the trans since it stays shuddering while in neutral. But thats all the help he is. He's not at all a car guy just a great engineer.
 

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Super Moderator
2010 DTS
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87,543 Posts
If it still shudders at 55 in neutral, and I would assume the engine is at idle at that point, then it has to be wheel related. Out of round tire, separated tire cord, out of balance wheel.
 

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Registered
1999 STS
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9 Posts
Discussion Starter #6
Front tires look good but are different tires. Cleared the codes and they all come back along with P1611 - Loss of CVRTD Serial Data which looks like the RSS lost comm with the IPC. SO I will worry about that one if it comes back. But as of right now Im back to my intermittent not starting problem I have in another post. Love this car but man does it have some issues to deal with. Good thing we got a good deal.

Would different tires up front even if they are in good shape cause this? I know these cars like things just right. I guess I should get all new rubber as a starting point with a road force and go from there right?
 

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Super Moderator
2010 DTS
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87,543 Posts
Right. Since the tires are mismatched, I'm assuming they are used? If you bought it that way, God only knows where those tires came from, what condition they are in or why they where replaced in the first place.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,738 Posts
Swap the front tires to the rear and report back with the results. Did the shudder get worse or better or not change at all?
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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71,004 Posts
Change to the same tire brand and size - the correct size for the car is on the driver's door spec sticker.

A cyclic shudder at speed with two different tires points directly at tire mismatch and imbalance. At speed, the two different tires (size, tread, treadwear) rotate at different rpm. As they go in and out of synchronization the imbalance comes into play and you get the shudder.

Very same principle as the sound of a twin engine airplane taking off: If one engine is very slightly faster/slower than the other, the "airplane sound" rises and falls as the propellers go in and out of synch. mmmmMMMmmmmMMMmmmmMMMmmmmMMM
 
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