Cadillac Repair: driveability/electrical concerns, vacuum lines, electrical concerns

Question
I am a shop owner working on a '90 Cadillac deville w/ 4.5PFI.When started cold, the vehicle tends to stumble and tries to quit. It misses badly and seems like it is being overfueled. Raising the Rpm and "clearing the engine" will help and the engine will idle normally. When warm the engine will run very well for 30 min or so and then do the same thing as when started cold, repeating the cycle. Vehicle was logging code 53. Flowchart for code 53 was followed and problem not found in testing.Distributor was replaced and logged code 53 once since replacement. I have checked TPS. Voltage ranges smoothly from about .9V-4.2V. Fuel pressure is normal.Fuel did leak down once but I am not convinced of a leaking injector.Fuel regulator is working correctly and is not leaking. MAP sensor was also checked.Measures 3.98 volts@ 0" vac, 1.75 volts@ 10" vac, 0.0V@24" vac.Engine produces good vacuum and is smooth.Wiring was inspected around distributor, and at PCM as well as connections checked. Power to distributor was checked, No visible leakage at fuel rail and no visibly damaged vacuum lines. EGR was also tested. Diaphragm will not hold vacuum. EGR valve should be replaced but its not being signalled "on" by vacuum when the problem with the vehicle occurs.I've include as much info I think as I can squeeze. Help Please! I currently have about twelve hours test driving and diagnostic time combined.Oh, also data was recorded with a scanner through several occurances but nothing appears to be wrong.

Answer
Hi,Ben

You may have a few things you need to check,these are notorious for causing your type of complaint,check the ground cable leading from the battery to the ground stud on the side of the block to the left of the starter the ground is mounted to the engine mount bracket,if this is loose it will cause drivability issues,and thats were your code 53 may be coming from,also check the injectors,ohm test them,anything under 12.5 ohms or over 17.0 ohms is a failed injector,they may flow ok,but have shorted internaly and you wont see that in flow tests,next tap test the ECM,90's were prone to having failed ECM's and will cause you to pull your hair out,tap testing on the case and wiggle test the wiring and connectors while running and see if the engine acts up.let me know what you find and if i can help you more.Do you need any Techs at your shop? :) just curious.Thanks


ED