Rough idle and bubbling noise under cab
I have a 91 GMC Sierra 1500 5.0 . It idles
rough at low speed sometimes stalling .
Runs fine at a higher speed . There's also
a bubbling noise under the cab like it's
coming from the muffler . But the noise
doesn't always happen . I have changed
the idle control valve PCV valve and fuel
Maybe you have a exhaust leak. Take it to a muffler shop. The rough idle could mean you need a tuneup or that the IAC is dirty or needs replacing.
What is the idle at? Maybe try running a can of sea foam through it
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