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Jerry Newton
Jerry Newton, Cadillac Technician
Category: Cadillac
Satisfied Customers: 4591
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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Cadillac Sedan DeVille: . I am purchasing a 1991 Cadillac

Customer Question

Hello. I am purchasing a 1991 Cadillac Sedan DeVille 4.9. with 71,000 miles. The engine sounds fine at idle when cold but when warmed up it runs rough and has a miss at idle and coming off idle to about 1,500 RPM. When you get past that point out on the road it pulls good. Checked fuel pressure: within spec. Checked spark: OK. Checked to see if injectors were firing with stethoscope: you could hear the solenoids working. The only code that comes up is a #30: ISC out of range but I don't think that would cause this problem. This afternoon I'm going to check the resistance on the injectors and spark plug wires. Do you have any suggestions???
Jerry Obenrader
Venus, Pa.
Submitted: 2 years ago.
Category: Cadillac
Expert:  Jerry Newton replied 2 years ago.
Checking resistance on injectors is exactly what I was going to recommend. We had troubles with these injectors back in the 90's.... and that was before all the newer additives started going into gasoline. These injectors don't tolerate the additives very well, resulting in internal failure of the coil windings, which you'll see on the ohmmeter as resistance that is lower than the specified 14-18 ohms. Check them when they're hot. If you have more than three that are shorted (<14 ohms) plan to replace them all.