1988 deville is surging..new plugs,wires,cap&rotor,modual.if I run headlights or heater it starts bucking. sometimes idles rough.Have replaced Dist.also All diagnostics read normal the machanic says.

potential air leak at the input to the computer?

you have built up carbon in your fuel system, try buying a bottle of Lucas that will clean up your fuel jets, you also need a engine cleaner Run a better octane gas not the highest but, one in the middle, than drive it by punching the gas peddle off and on quickly to blow out the exhaust lines and your eg valve that builds up carbon and also the lines, sometime these have to be taken off and c leaned manually in a bucked of kerosene good luck

Hello first of all

In reading your issue at hand not having no spark there is only a few things that can cause this being that its a 1988 car i will list below what you need to go over and check.

1.spark plug wires
2. distributor cap
3. ignition rotor
4. coil pick up
5. faulty distributor

That being said most are a easy and cheap fix plug wires run about 20-35 bucks autozones duralast brand , distributor cap runs between 7-18 bucks , ignition rotor 3-8 bucks , coil pick up about 15-30 bucks all at autozone.

Now there is no real way to tell if there bad but a good examination of the distributor cap and rotor should tell you corroded inside cracked worn down.

i would start with distributor cap , ignition rotor, coil pick up if the car starts after this replace spark plugs wires. If that does not fix it most likely you distributor is faulty itself.

i hope it helps if so could you leave me so 4 thumbs up feedback thanks so much

Oxygen sensor only report the condition of the engine the rough running condition can range from a worn sparkplug wires to worn sparkplugs to valve problems to injector problems. with the cadillac deville a tune up should be the first attempt to smooth the rough idle with the inspection of the cap and rotor cap and rotor do have a tendancy to arc internally and create misfire so does sparkplug wire that can leak spark voltage to ground and create misfire. the spark plug wire especially if they are brittle and hard can create issues

check fuel pressure

did you change the fuel filter? make sure all plug wires are on the right plug If the coil wire was crapped out the other wires may me too. look at the inside of the cap srpray some wd 40 in it and wipe it out good make sure top of rotor is clean too

try checking the coil for leaks. if it looks discolored anywhere on the coils then it's leaking. i had the same problem with mine. sounds like the same thing mine was doing untill i replaced the coil. could also be the drive gear for the distributor to but highly unlikely

try replacing the throttle position sensor

Had a computer on my 1990 Cadillac Deville bad, after changing plugs, wires, cap, fuel injectors, egr valve, etc.

The computer was not firing an injector and i had a miss and rough running mostly at 35 mph on the roads. It bucked like a bull.in a rodeo.

How about plug wires they are sometimes the problem if plugs arent getting proper fire they sure do look bad .. look for any burns and check them close