Originally Posted By: LT4 Vette
The IAC (Idle Air Control) valve is probably very clogged up with grime. You will have to remove it and use a flat edge screwdriver to clean the wire mesh screen that is all clogged up.
I would also remove the throtle body and clean it with a rag as it also tends to build up grime as the miles add up.
Same thing happened to our 1998 Civic.
+1 This would be my sugguestion. Also when was the last time you did a tune up with plugs/wires and an air filter?
What about the condition of the PCV?
These are other things to check other than LT4 Vette's advice.
I know it's OBD-II I just don't know if the computers were that sophisticated back in '98 that it would know if the IAC was out of range or carboned up. I don't know Honda that well, that's why I said might...
These Civics are ULTRA reliable with basic maintenance.
Our old 1998 Civic is approaching 250K miles (nephew now drives it) and the only problem the car ever had was a cracked exhaust mainfold ($85) at 160K miles and I installed a new Denso O2 sensor due to the mileage. Other than that, everything is still original on the car except maintenance items and the TBelt & WP.
BTW, if your car stalls (which out Civic did) and you scan the OBD for codes, it will not show any if your IAC is clogged.
All vacuum lines and connections must be perfect, including the intake. Check and repair as necessary.
The PCV system is critical - trace it and check all of it.
Clean the throttle body bore and plate really clean with solvent and a rag.
All this is easy to do, just a bit of time.
If she still has problems, clean the idle air motor valve.
Be careful with strong solvents on the valve.