Brakeight fuse which fuse is for the brake lights on a 1984 coupe deville

Empty the gas tank, fill with good gas.

check your timing. Cadillac use to use a plastic timing gear that would easily strip. Replace it with an aftermarket gear made of metal and you won't have problems for a long time. Why they used a plastic timing gear is the stupidest thing I have ever heard of and when I found that out I vowed to never buy a cadillac again.

most likely a bad throttle position switch or an vaccum leak. try spraying all hoses and the intake with carb clean if the rpms change that object needs to be repaired

check wiring u might have a wire rubbing some wheere

I A C motor small part on throttle body ,controls idle mixture when they fail at idle the engine "hunts" for proper air/fuel mixture . when defective it causes o2 sensors and TPS to compete to set an idle thus the up n down effect.. auto wreckers if your broke new from your local parts store....dealer to much 1 plug in two bolts for most applications

Fig. 31: Vacuum circuits - 1984 V8 4.1L engine Fed. and High Alt. (DFI)

Fig. 33: Vacuum circuits - 1984 V8 4.1L engine Calif. (DFI)

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Jose.

run the fault codes and check for a problem reverse servo/solenoid

could be either, you need to see it on a hoist to locate exact leak,

Before you replace the (TPS) Disconnect the negative battery cable. When you reconnect the battery the computor will be reset. Please make sure you put the new snsor in as you took it out should be fine..

just go through them all one by one until you find the fuse