Low Idle - Diagnosis Needed

[rosettiski]

My 1996 I-30 has 160K miles on it. It has recently developed a "low idle" (400-500 rpm, vs. the normal 700 rpm), particularly when the engine isn't warmed up, but intermittantly at other times as well. The engine performance seems normal when driving at speed....

I replaced the NGK plugs recently to no effect; I also cleaned out the spark plug tubes (one tube had a little oil in it, but that has not seemed to reappear). What should I be looking for next, perhaps in order of likeliness, to be causing the problem? I relatively new at wrenching....

Thanks in advance.

[NutriaforBreakfast]

Try the idle air control valve furst
You need to SLOWLY unscrew the plastic bolt that lets air
in and see if the RPM increases
If that doesn't work you may need to remove the IACV
and clean it-its probably carboned up. I think you search
the threads for this because the floor shop manual and
Chiltons don't have this-but it does work!

I found carbon had hampered engine performance on the IACV
and on the EGR tube going into the upper intake manifold
(on the back by the firewall) and had to clean them out.

[rosettiski]

Thanks for the help. After loosening up the plastic bolt, my RPM speed has become more stable. Will continue to monitor same, and will mvoe ahead with IACV cleaning if needed....

Thanks again.