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Solved! - Diagnosis help, weird rough idle after head gasket job. 900 1995

posted by  drewb on  Sun Jun 29 08:41 CST 2008
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last visit: Sat Jan 18 12:44 CST 2014
[RELATED]

Thanks, yes I checked and rechecked everything. Several hours of time. Turned out I had reversed the two vacuum lines on the EGR valve.

Here's my theory of the strange symptoms (and I'm sticking to it):

When the car started the reversed lines opened the EGR valve fully. Since it was idling and not passing too much exhaust the computer was able to compensate. Giving it gas sent a blast of exhaust that the computer found out of range. It went nuts, never finding a good setting for some time (I forgot to mention that it would settle down after several minutes). Strange thing is it never set an OBD code.

I found it when I burned myself on the EGR tube where it goes into the intake manifold. A light bulb went off, it should never be this hot. Only if the valve was stuck open could it get "exhaust manifold hot" since it is downstream of the valve.






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