I need some help here. MY 87 Ranger 2.3l failed its smog test for the first time ever. It has ideling rough, some times very bad and some times not much. It seems worse when engine is cold. It passed the smog test fine on the high rpm part of the test and runs well on the high end while driveing. It failed the HC part of the test. I dont see any easy to find vacume leaks. A friend suggested doing a tune up but it hasnt been very long since i did that. And it runs well at high rpm. So i dont think that is the answer. Any ideas or thoughts will be helpfull. And if there is any legal tricks of the trade to help them pass? IM some what pressed for time to get it figured out. Thanks joe

 

High HC is the result of poor (incomplete) combustion. Ignition misfires are most often associated with high HC, but that's not always the case. For example, a stuck-open EGR valve can cause a rough idle, incomplete burning and high HC.

 

The catalytic converter is probably worn out also.

 

Get some O2 safe carb cleaner. Remove the throttle plate using a 12pt long socket. Look inside the upper intake. Bet you'll find a coating of carbon goo. Use the cleaner to wash down the inside of the intake. Let it sit for a half an hour. Re-assemble and start the engine. You'll get a cloud of crud, but it will clear up.
My truck failed smog check with less than 5 thousand miles. Never did pass. I found cleaning the intake helped, and cut the HC reading significantly. After doing this, it has passed with no problem every time.
As far as the catalytic, it uses a catalyst, which works until it is fouled or coated with poisons. I have the original on my 1987 vulcan in a Sable. Over 230k and it still passes.
You pays your money and you takes your chance.
tom