Handy930

Mark, I see a couple of fuel test unit at Pelican. Basic for about $100 and one with AFR meter for about 250. I think I'll pop for the basic. Messed with it this afternoon. Plugs look good. checked over vacuum hoses. No improvement. It seems to be a problem at 2200 in second and less in third. In forth at 2200 I don't detect the surge. It is more apparent when the throttle is very feathered. I found the air sensor plate very dirty and cleaned that up thinking it could be the culprit but no change. Dosed with Techron and will see what happens with this tank of fuel. Could the BOV or decelvalve be suspect? Starting to drive me nuts.

Mark Houghton

I doubt the BOV (boost recirc valve) is the issue. It would only show it's ugly head under boost conditions. The decel valve could be leaking and drawing air into the intake continuously, but I would think you'ld see high idle as a result and other such weird symptoms. I still think you're up against fuel delivery/control issues.
Get the gauges and test your system. Even if it doesn't point to the problem, the gauge is good to have regardless. Is this the one you were looking at on Pelican?>>>> http://www.pelicanparts.com/cgi-bin/...%20with%20Case

Handy930

Mark, I sent a response but it must have gone off somewhere besides here. Checked plugs, OK. Checked vacuum hoses, found nothing. The air sensor plate was very dirty and cleaned, no change. The engine at 2200 in second you can feel the surge. Third gear at 2200 less. Forth at 2200 cannot detect anything. Seems to be when the throttle is very feathered. Looked up the Pelican fuel test rig. They have the basic for about $100 and the other with AFR meter for $250. Thinking basic. This is driving me nuts. What about the decel valve? Could it be causing this? Also, the surge seems a little less when cold and then more when warm. Warm up regulator? We'll see how the fuel pressure tests go. Thanks for you input.

Handy930

Mark, now I see my first response don't know what happened. Yes that is the rig I'm looking at. I could eliminate the decel valve. But I will wait until I check out the fuel system. Thanks again.

Handy930

I did eliminate the decel valve, but no change. I am starting to think I have an air leak somewhere. After I pulled the decel I forgot to plug the vacuum line and went for a test. Of course the idle was very fast and the surge was even worse. So while I wait for the fuel test rig I will continue to look for other points of air entry. I will post the results.

Handy930

Just finished testing the fuel system. Cold pressure and system pressure OK to spec. Warm pressure I think is OK it took about 5 minutes to build to 3.8 bars. My manual just says the time will vary depending on the temperature. Holding pressure OK to spec after 10 and 20 minutes. Only thing I have not checked is the " warm full throttle enrichment pressure" and fuel delivery rate, but cannot believe it is causing my problem. The low rpm surge seems to be getting better the longer I drive with a load of Techron in the fuel. This makes me think injectors. Problem now is the weather snow/ice and cold. So I will have to wait for a good day or two to see how it is running. If I had an injector not performing wouldn't I get excess popping in the exhaust when I let off? I have this and it did seem to become more noticeable lately. If it doesn't clear up then I will check out the injectors. I will post results as they occur.

Mark Houghton

Well you're doing the right thing by systematically taking things out of the equation. How long has it been since you replaced the fuel filter? Want to make sure there isn't an obstruction happening there.

Your comments on the Techron seeming to help and your earlier comment "...at around 2200 and steady in 2nd, I will get an occasional pop out of the exhaust" may indeed point to injector health. There's a good post somewhere (I think it's on Pelican) that will walk you through cleaning (backflushing) injectors as well as flow balancing them - if you care to go through the effort - or just send them off to be professionally cleaned and checked. I used the guys (John, I think was his name) at Specialy Auto to clean mine. Good service, quick turnaround, reasonable price. http://www.specialtauto.com/porsche-parts/index.html

Handy930

Mark, I'll check out the Pelican thread and/or Specialtyauto. Thanks for the tip.

Mark Houghton

This is the posting I was referring to...DIY injector cleaning. Just be gentle when pulling out the pintle.
http://forums.pelicanparts.com/911-9...how-clean.html