I seem to have solved the Code 18 and Code 17 issues I had with my '93 Buick LeSabre. I switched out the coils, wires, and plugs and it ran great for a couple of weeks. Then I had a new issue

One day I drove to a nearby city and stopped and started the car several times without issues. I came home and had to go back out about an hour later to pick up something at a shop. When I came out of the shop the car would crank but did not want to start. I cut the switch off and tried again and after a few rounds of the engine it fired but was running rough. I managed to drive it home but at idle the idle was rough; it was hard to tell if it was missing or not. The next day I decided to change the fuel filter since I had one but had never installed it due to the fact it is burried under the car and you have to jack the front end up and crawl in under the side of the car. What a stupid location for a fuel filter. After changing the fuel filter, the car appeared to run fine. However, that was short lived.

The rough idle came back. Then it left again and ran fine for a few days. Then it came back and I had to drive it 18 miles to work and then back and it ran rough the whole time, a rough idle and I could feel it even when traveling down the road at 50 to 60 miles an hour. At one time yesterday on the way home it stopped once, only to reappear. Today it was idling rough when I pulled it into the shed. Then I started the car again to move it a bit further in the shed and it was idling smooth.

I don't think it is a ignition problem; although it might be related to the cheap chinese coils I put on the car. I am thinking it might be the injectors but since it is coming and going, mostly coming now, would it be a failing injector or simply a wiring issue?

I am not familar with injector failure. I do add injector clearner to the fuel at regular times because I have heard of problems with ethanol gasolines (which is becoming impossible not to run since it basically increases fuel consumption; however, that is another rant for another day). What I am looking for is some feedback on what/how to dignose this issue. Oh, no check engine lights, no codes stored in the computer. I don't have a way at this time to record any real time data since my brother-in-law gave away the scan tool I borrowed the last time.

Have you tried cleaning the MAF Sensor and IAC valve?

It has a new MAF sensor, put on last summer when I was having the stalling problem. The car sat from November until I got the Code 18 solved with the ignition parts I outlined above. Also has a new ICM as well. I took the IAC valve out last year and checked it and cleaned it. It could be the IAC is starting to fail and is just not setting a code. I just checked the resistance on each injector and they all read the same. Wondering if I should bother doing a noid light check on the injector connectors; it would only tell me something if the engine is running rough and it was idling smooth when I turned it off after pulling into the shed.

I need to add that this issue has nothing to do with either a warm or cold engine as it happens either hot or cold engine.

Could be a bad fuel pressure regulator, or low fuel pressure at the rail. Pull the vacuum line off of the regulator, and see if gas drips out, or if it smells like gas. You'll need a fuel pressure gauge to check pressure at the fuel rail; you might be able to rent one from Autozone or other parts store.

I have pulled the vacuum line off the regulator and saw no gas or smell of gas. The last time I checked the fuel pressure; when I changed the fuel filter, it was steady at idle of ~40 psi. According to my shop manual, the fuel pressure for '93 LeSabre 3800 is 41 to 47 psi so I would say the fuel pressure is within specifications.

I cleaned the injector connectors and plug them back in without doing the noid light test. The engine ran fine so it is hard to pinpoint the problem. Perhaps it was an injector not wanting to fire but why? As I said, an ohm test showed all injectors with the same reading.

My other guess would be the computer not controlling things correctly; it may be what is starting to fail. My brother-in-law drove home one day on a car that was running horribly; came to find out it was the computer. The Code 17; spark reference, can also be caused by a bad computer. The Code 17 is gone and I thought maybe it was set by a bad ignition wire I had on the car. I guess I will see tomorrow if the rough idle reappears.

I apologise for not finishing this thread up. I have gotten busy in a major project that is taking a lot of my time. As far as I know, this problem was caused by the egr valve(*) sticking open. One day when it went to running rough, I tapped on the egr valves and it smoothed out. I took the egr valve apart and clean the solenoids and coated them with a dry lubricant. The problem went away for the most part. A couple of times I have had it to briefly return only to go away. I may have to do the cleaning thing again. The egr "pack" on this car is expensive to replace so unless it fails completely, I will continue to just clean the solenoids to make sure they don't stick open.