Started rough idling a couple days ago, engine RPM hot idle in gear seems to be about 100RPM higher than normal. otherwise it runs well. Only codes showing are 12 and 77. Engine has 67K miles. Was supposedly tuned up 10K miles ago (when we bought it). Any ideas?
A very popular problem with these engines is the intake manifold gasket develops a vaccume leak causing a rough idle. I think the gasket kit is fairly inexpensive and the job isn't too terrible. Has the fuel filter been changed when it was tuned up? Were the dual throttle bodies cleaned out? These items would be a start in your diagnosing.
I agree- the faster than normal idle indicates a vacuum leak.
Cheap is right- about $5 at NAPA:
Thanks to those who replied.
After checking the usual, plugs, wires and for vacuum leaks I went ahead and changed the intake gasket. The miss at idle appears to be gone, the idle speed is back at its usual RPM. Exhaust flow is smooth.
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