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I have a 94 SLS with 180,000 and am experiencing a surge or miss between 35 and 50 mph. Everthing is fine below and above those speeds. And i get the same surge whether accerlating or just cruising along. Any suggestions.


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I'm assuming there have not been any diagnostic codes (search [30-days and older] for how to look those codes up).

If not any codes, etc, this surge/miss/chuggle/vibration might be the infamous transmission lockup effect (may be called something else). When the torque converter locks-up for economy as it should around 35-50 - it can amplify other minor engine miss/vibration problems - that are otherwise un-noticed.

Anyway, to test for the tranny lockup effect, cruise on a level smooth road, typical to make the problem occur. Miantain the accel pedal lightly - and lightly touch the brake pedal (only enough to lightup the brake lights). The tranny will "unlock" at that point and if this is a "chuggle" - it will cease.

If the effect goes away when the brake light is lit - then you might want to determine the "root cause". Note, this "chuggle" is not a tranny problem per se and is probably not causing any damage if it only shows up at a very specific road speed and engine/tranny load. Mechanically speaking, its probably something about the confluence of various harmonics manifesting to a cognitive level (whew, I need a drink).... If the Caddy wasn't so smooth otherwise - you probably wouldn't notice it.

From what I have read - the '94 engine need the "phenolic spacers" under the intake cover cleaned out every few years. Of course, the plugs might also need to be changed, but there are little or no other tuneup items to address. I think that significant repair requirements, like FPR (Fuel Pressure Regulator) or the like - would have resulted in many more drivability problems already.

One other maint item for that era Caddy - like mine, is coolant drain/change (with Bars Gold added to rad hose).

Good luck

Add power to leave problems behind. Most braking is just - poor planning.
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