engine surging

Have been having a continuing issue with low/rough idle on stb engine. Have checked out and replaced a large number of parts to chase down the cause, with little luck but the engine has this behavior and I am wondering if it can lead to an answer for my idle issue. Idle while rough is consistent in other words it stays at @ 650. If I bump up the rpms to between 1200 and 1600, in neutral the engine begins to "hunt" the rpms will begin to surge up and down a couple of hundred rpms, then it will settle, then it will begin to surge again, settle, surge, etc. If I go beyond 1600 the surging stops, if I go below 1200 the surging stops. Timing set ok, new plugs, wires, distributor installed end of last season.
Engine is 8.2 MPI Crusader.
Any ideas as to why it would surge like this. It does not do any surging while under load (in gear).

Vacuum leak?


Jeff

surge shows in the symptoms for the MAP sensor area. Check the vacuum line going to it as well as the harness and connector.

I will check to see if there is a vacuum leak, what is the normal reading for this engine?

One of the service manuals recommends checking at idle+ (800-1000 rpm) before diagnosing the MAP sensor: they want at least 14 in Hg of vacuum.

Do you wanna couple PDFs for the MAP tests?

That would be great, I have the service manual for this engine (got it from this site), and was going through it last night, I do not have a scan tool, have the old fashioned vacuum gauge though, I also have a voltmeter I can use as well. what I was going to do is just swap out the port MAP with the stb and see if that changes anything.
my email is [email protected] if you want to send the PDF's there.
Thanks. I have checked the vacuum on this engine to try and diagnose the idle issue and it is in the 14 hg range, but my vacuum gauge is almost as old as I am... but this engine also has a lower fuel pressure than the port engine, 39 psi at idle vs. 43 psi I know that fuel pressure can be affected by vacuum or the lack thereof so I am wondering if that is my "ghost" that I have been chasing for several seasons. Any suggestions regarding procedures for testing vacuum would be helpful as well.

Mark,
I got the PDF's, thanks alot, if they help me solve this problem I'll send ya a case a beer or your favorite bottle of Scotch...
Scott

Glad they made it intact.

If you look on the page 91 (physical page count) you'll find a troubleshooting start list. Based on your previous posts, the buzzwords to search on are "surge" & "exhaust odor".

The beer is much cheaper than the scotch; tnx for the offer.

make any progress?

Have not been able to get down in the engine room yet, had a bad storm rip though the marina and take out my entire front enclosure, I mean that it was GONE... blew away never to be seen again... I will let you know though. Thanks for your help.