Im not new at cars, I've been messing with motor for years, also I'm and A&P mechanic


anyway, I bought my brother 99 Civic EX with a blown D16y8. I found good deal on a D16y8 from a 96 EX (just the longblock).


Swapped the motor in and i now have a high idle problem about 1500rpm although if you give it a minute it will go down to 1100. threw a CEL for "high idle"
There a very loud "rushing air" sound sounded originally to come from the fuel rail, but using a tube, it appears to come from the area below the valve cover where the intake and motor meet.
I replaced the intake gasket with a felpro ms91553. Did not fix

I've checked every vacuum line and none are leaking. I took the IAC apart and cleaned it, bench tested it to verify the motor was working. didn't help.


I did some searched here and on other civic forums, and found a couple vague posts saying there are two different d16y8 intakes any time i search for one though, there always listed as a 96-00.
Felpro shows two different part number for gaskets... 91553 for a '99 and 91485 for a '96
majestic honda web site says a '99 civic intake manifold PN: is 19564 and the '96 is 19563

So this appears to maybe be the problem.



So how do i fix it? do i have to get a new intake for a '96 civic? can they be adapted or the leak plugged?
Any help is appreciated.
Ken

 

Vacuum leak anywhere will cause it to idle high out of control. So it is apparent that your manifold is not sealing properly.

I'm not sure exactly what can be done but assuming you still have the old engine, the obvious thing is to look at the two heads and see how the ports are different. It could be related to the EGR system, I don't know if either had EGR but it does run thru ports in the manifold at cylinder 4.