car = 1985 300zx non turbo with the VG30E engine and 155,000 miles. One owner car maintained regularly.

Recently I replaced the valve cover gaskets to stop some oil leaks. As part of the process, I found that the idle up sensor was defective and replaced it too. To replace the driver side valve cover gasket, it was necessary to remove the intake manifold collector and all of the connecting hoses, etc. I replaced the intake manifold collector gasket, but all else save the idle up sensor were reintalled as is.

My problem now is that I have a very rough idle. I have checked the EGR valve, PCV valve, reset the throttle valve switch, run the ECCS diagnostics with no failure codes to report, checked all the vacuum hoses.

The car accelerates fine. At city street and highway speed there is a periodic buck.

Any thoughts?