rough idle

A rough idle could be a large vacuum leak that can lean the air/fuel mixture out to such an extent that an engine will not idle at all. An EGR valve that is stuck open at idle can have the same effect as a vacuum leak. So too can a loose positive crankcase ventilation (PCV) hose, a leaky PCV valve or the wrong PCV valve (one that flows too much air for the application). If somebody replaced the PCV valve recently, they may have installed the wrong PCV valve. The rough idle in all of these cases is caused by "lean misfire." The fuel mixture is too lean to ignite reliably so it often misfires and fails to ignite at all. Lean misfire will show up as elevated hydrocarbon (HC) readings in the exhaust, which may be enough to cause a vehicle to fail an emissions test.

Thank you rasmataz for a promt post, here is just a bit more info. so you think it the EGR or the PCV. Ok good info thank you so much. happy new to all



I went and had an oil change yesterday with smog check which passed with flying colors.
Trying to start the van today, with keys in the ignition and turned, there was a sudden pop, the start tried but hesitated then tried to start for which was not continued as the pop and hesitation had me immediately turn the van off knowing something was not right. When the pop occured, the car was silent and nothing else as if the van was not tried to be started yet.

After a second start, the van started however, and now it idles rough 500 to 1000 rmps with small surges. OK now am i fubar?


thanks for any help and have a happy new year and a safe 2010

will driving the van hurt the motor? got to go to work sat the drive is 4.5 miles

Try checking these additional items:

Running rough and misfiring can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.

I had a mind boggling problem with my 3.8 Ford v-6. Ck engine light came on, Oreilly's scanner said "missfire cyl 6" so I put a coil pack on , no help, i switched plugs & wires with 5 & 6 and still cyl 6 would make no difference when I pulled away wire, compression test was 180lbs,Put a fuel injector new on #6, no help, I put a cam sensor on, no help, then a crank sensor, then the Ignition control module (mounted on inner fender) still #6 missed, then this weekend I pulled off plenium then lower intake & replaced gaskets, still # 6 miss, so today i went to junkyard & put a used MAINcomputer (in firewall) & bam it has no miss

Excellent addition to this thread! Please feel free to help out whenever you are on the site :)