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I have a 93 deville with about 152k on it. it's been running fine for a car that's been through as much as it has. but today i was going 45 in a 40, so i took my foot off the pedal, i was just going to coast down to 40. the thing is it didn't decelerate. it stay at 45 like like i was in cruise control. and it was really smooth. all of the sudden it had alot more power. I thought to myself "the caddy's frisky today" when I got home and turned it off, there was like this thumping from around the brake pedal. I got out and looked under car to see if there was any fluid under the car. the thumping stopped and the leveling pump came on as soon as i got out. i've been driving it for about 4 years now, and it's never done anything like that before. i just hope my tranny's not going out. does anyone know what it might be, any info would be appreciated.
Thank You, Jesse
 

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The thumping sound was probably the ISC ratcheting. The compressor coming on AFTER you got out is a little strange but it could just be a cooincidence. Either way, I wouldn't translate it into your trans going.
 

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Welcome lowmank ....... Thanks for signing up :wave:
 

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My car does the same thing and I replaced the TPS adjusted it and it quit for a week and now its doing it again. not to mention it also starts real rough when is cold. it idles back and forth until it smooths out after about 30 secs to a min. I need the same help you do :bonkers:
 

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thats funny, my 93 deville did the same thing (with the idle) when I first got it, then it went away, I thought maybee it was a carbon deposit holding the butterfly on the throttle body open, anyway, with the pump running, its no biggie, both my deville's pumps occasionally run after the car has been shut off, its just maintaining pressure. The early models, (I think 88 and below models) the pumps only ran when the car was turned on, but after 88 they run whenever needed. So don't worry about that. The thumping noise was probably your compressor, the little noise insulator grommets that secure it might be a little worn, sometimes when the pump first turns on it has to work a little harder to pump up so it will run a little rough untill it builds up pressure, I have noticed that on my devilles also. For the idle thing, try reading the codes, if its a sensor most likely it will pop a code, if not, I took mine to Cadillac and had them clean the throttle body and injectors, actually I do it once every couple of years, and they never have any problems.

Jack
 
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