security system wont start and rough idle

there was a security system in this car. 1993
over the years it sometimes wont start. there is a security key input under the dash and sometimes bumping it or kicking it would allow it to start. several weeks ago it stopped starting up all together. towed to a shop and they tried to replace the computer module. the junkyard one didnt match or something and they got another one that i guess worked. but it didnt fix the starting problem. they replace the ignition or at least something in the steering column and ripped out the security system.. i pick it up and hey, it starts but the engine idle is very rough. sounds like a spark plug is missing or something. amateur over here.

at this point i dont know if i have the original computer module or the one from the junkyard. if its the one from the junkyard, could that be causing the rough idle?

i replace the fuel filter and it helped but still idles horrible. is it safe to unplug the wires one at a time while its running to see which one might be effecting the idle? or do you unplug one with the engine off and then restart the engine? broke financially so i got to try everything that i can. thanks for any tips.

Do you still have the original module? If so, swap the two and see if that's the current problem. If not, call the shop and get it back. Easy swap, located near the passenger floor under the glove compartment I believe.

Don't know if they played with the spark plug wiring while trying to fix it. Might as well check something easy; the firing order.

http://autorepair.about.com/library/firing_orders/bl-fo-7486.htm

I believe the 94 is the same as the 93. While checking, also look for rusted ends.

Too many things this could be. Good luck

well after spending 500 last week to get the car to start again it decided to not start again yesterday. no cranking at all. a few hours later it started to crank again. dropped it off at the shop today. i will have them see what computer module is in there and see if they can finally get rid of the no start issue. what a pain

wanted to post an update. they told me it was the same computer module and of coarse they had no problem starting the car. this is the original problem. every so often it wont crank and then hours or days later it cranks again. i have a feeling it is going to continue as always even though i have already paid 500 to "fix" it.
so the rough idle that wasnt present when the car last was driven is going to cost me 400. they say the "fix" is to replace both of the gaskets for the air intake manifold. it must of been a "co-incidence" that the gasket failed during the few weeks that the car didnt start. picking it up tomorrow. so it should start and run smooth like it did, yea right, we will see.
as you can tell, i am a bit sick of this.