Help! 1992 Base Coupe Runs Rough If It Hasn't Been Driven In A Few Weeks.

[boiler55126]

I have a 1992 base coupe with 60K miles on it. If the car sits for a couple weeks or more it will run rough. It starts fine but it runs real rough unless I drive it for about 8 miles and then it runs just fine. It also does this if I've driven the car and got the engine warmed up, then shut it off and if I go to restart it about 45 minutes to 1 hour later it starts hard and runs rough for about the first mile I drive it. What I mean by "starts hard" is that it cranks much longer than it should before it starts. If I start the car anywhere from 5 minutes to 40 minutes after I shut it off it starts fine and runs fine. Early this spring when I started it for the first time this year it started fine and I let it run at idle for a long time. After a while it began to idle rough just like if you don't drive it for a few weeks. What I did notice though is there was white smoke coming from the drivers side exhaust. It didn't smell like antifreeze. It smelled more like gas. It doesn't appear to use any coolant. A few things I know it's not: The fuel injectors, tested them and they don't leak at all, the fuel pressure regulator is fine, I had a fuel pressure gauge on it for about 1 hour with the engine off after I had the engine warmed up and the pressure never dropped, it stayed around 40 p.s.i. I've replaced the spark plugs too. The check engine light never comes on so there is no diagnostic codes. Any advice would be appreciated. Thanks.

 

[Antz81]

White smoke can be either coolant or unburnt fuel. Since you say it smells like gas and there doesn't seem to be any signs of it being a head gasket other than the running rough it's most likely unburnt fuel.
This makes me think you have a misfire somewhere. You've already replaced your spark plugs so we can eliminate those. Next i would check the leads are all on tight and in good condition. A timing light will be able to tell you if they are firing or not.
You say the engine light doesn't come on so no codes, I assume that it does light up at all of the normal times though. Also I know with some fault codes the ECM stores them but doesn't necessarily bring the check engine light on. Not sure if there would be any on a 92 though.

 

[boiler55126]

It definitely has a misfire. You can hear it afterfire in the exhaust also. What's weird is that it only does it if I haven't driven the car for a while or if the engine has been up to full temp. and then I shut it off and let it sit for about 45 minutes. I know the opti-spark distributor is a piece of crap and causes problems and I can understand that being a possible issue when the engine is warm and it starts hard and misfires after it being off for 45 minutes or more because the distributor could be getting heat soaked. But it doesn't explain why it does the same thing happens when I haven't driven it for a few weeks. It seems to be fuel related to me. Or possibly an O2 sensor. But if it was an O2 sensor I would think the check engine light would come on.

 

[Antz81]

O2 sensor would not cause a misfire, no matter how bad it was.
Unless you're not getting fuel to a cylinder then fuel is probably not the issue. Very low fuel or way too much could cause it, but that would have to be extremes (flooding)
As for it only being after it's sat for a few weeks, I've seen all sorts of weird intermittent electrical faults. So I wouldn't dismiss it just because of that.