Unless there is some bad wiring between the ICM wiring harness and the firewall, or the firewall to PCM harness I have no idea. I examined the PCM connector under a high powered lens and found no problem.

Someone that was a GM tech is going to come and look at the car with a better scan tool. I was hoping that was going to be this weekend but it probably will have to wait until next weekend.

The rough idling could be due to the fuel injectors being reinitialised due to the code 18 or it could be that the PCM has not had time to recalibrate from the battery being unplugged. Either way, the code 18 still needs to be addressed and fixed because it can cause a stumble or miss in the engine according to the GM shop manual. I was going to talk to the GM tech about if the car can be driven with this error or not. Since it is a 1993, I don't have to worry about the CEL not letting me get the car inspected.

I came across a blog on the net by a mechanic who is also a writer. I located a contact for him and posted my problem to him. He responded with the following:

Now I have had the ICM mounting bracket off the car and I cleaned the ground connector and where it is mounted to the engine. I also did a "beep" continuity test using an ohmmeter between the mounting bracket and the alternator casing and got a strong "beep" out of my meter. I have almost forgotten the Code 17; spark reference, that was set at one time that went away. Maybe it is the coil pack; what does everyone think? This is the first positive lead I have had for some time.

Problem is, on his car it was the 1/4 coil but even if you have the same issue it could be any of the coils. You would have to replace all 3. I don't have time to read this entire thread, but have you pulled each coil and checked for resistance across the bottom, as well as the top, leads? If you do that and find one to be inconsistent with the others, you may have located a problem. I don't understand how this relates to a code 17 or 18 though.

Remember that this is an OBD-I engine with a lot less information than is provided by OBD-II and other diagnostics found on newer cars. I did to an ohm test on the secondary but did not do a check on the primary. I haven't had the time to pull the coils and do that but will. My understanding is that a misfire is interpreted by the PCM as the code 18. It may not be the coils causing the problem but I do know that it is not what is listed in the GM shop manual because all of that has been checked and/or swapped out.

Ordered a set of Chinese made coils from a parts shop on ebay for $40 (set of three). Put the coils on the car and ran until engine was hot and no Code 18. Did not road test. Valves a bit noisy (rattle) but the engine does have 323K+ miles on it. Might try some of that Seafoam stuff in the oil.

Oh Kim, I wish you wouldn't have bought those chinese coils. I'm afraid your going to be back to square one here sooner or later.

Yes Mike, I am aware of that. However, when you make below the poverty level, way below the poverty level (and I not joking here) then you are forced to buy cheap parts and hope they last until maybe you can afford better. That is why I am still driving a car that has over 323K+ miles and is 19 years old and it is the only car I have (outside of Mum'* old '83 car that is far from road ready). I would love to own a car made in the 2000s but that is not going to happen any time soon.

BWD Select Ignition Coil : $35.99 each X 3 = $107.97 plus tax.

ACDelco Ignition Coil : $62.19 each X 3 = $186.57 plus tax

Cheap China coils $39.95 for 3 + free shipping + no tax.

Yes, they are probably cheaply made and won't last long but at least I figured out the problem and I can always replace the coils later (they came with a 60 day warranty) if they go bad.

I realize the OEM ones are expensive, but I hope they don't leave you stranded somewhere.

I hope so as well. Last year when I started having problems with my car I had to beg to get a tow home. I called my insurance agent and got him to add towing to my auto insurance; $6.40 every six months and I had to use it one day when I thought I had the stalling problem fixed but didn't. I was only six miles from home but that is still a long ways to walk.

Thanks Mike for caring