911SC tuning problem

[kingbird6]

Maybe some of you guys can save me some trial and error money here: My 82 SC recently started getting a flat spot and a surging at about 4,500 RPM on up but only on full throttle, otherwise it seems to have good driveability.

My idle was too high and a new shop I visted diagnosed that as a faulty distributor advance which I replaced with a rebuilt distrbutor and that at least fixed that issue. The car when cold however wants to die if the RMP drops off from depressing the clutch pedal but if I catch the throttle before she drops to nothing she'll idle fine and once it's warm I'm good with no dying. So, I could have two separate issues going on.

I have never replaced the 02 sensor and the car has 132K miles on it....Maybe one issue so I am replacing that for sure..

The injector seals were replaced last year but the manifold boots are swollen like balloons so I might have a vacuum leak. Any other ideas while I have the motor dropped ? Thanks

Brian

[Trotskyite]

My car did the exact same thing. It was a combination of things though. I replaced: injector seals, new airbox ( old one turned out to be cracked even though I had installed a pop-off valve a few months earlier), full exhaust backdate with oxygen sensor delete and a few miscellaneous things. Runs like a champ now. Could also be a blockage in your cat...

[OldTee]

My 78 is doing the same thing. The fuel distributor is new and I think it was replaced for this reason by the PO. We set the mixture the other day and the numbers are : CO = 2.87, CO2= 13.0, HC = 732, O2 = 0.6. Idle was set to 810rpm. The air pump belt was removed. I have since readjusted the idle upwards to make it somewhat drivable. It has new injectors and seals. I am pulling the engine this winter to remove the rest of the air pump stuff, add Carrera chain tensioners, Cat by-pass, replace the soft looking intake rubber hoses, fix a oil leak. Engine has 1000 miles on a rebuild 9 years ago (the car sat just after all that engine work). Total milage on the car is 70K miles.

Any ideas?

[kingbird6]

Thanks for the ideas. I will let you guys know what it is as I will be dropping the motor this Saturday and replacing the intake boots and checking for vaccum leaks. I'll test it and then see if I also need to put in a new OX sensor so i can isolate the problem. If that doesn't work I will install my cat bipass pipe. If that isn't it then I'll take it to a shop and let them narrow it down for me.

[Gunter]

Try running with the OX sensor disconnected and the mixture readjusted with the long 3mm Allen.
Check for vac leaks before you drop the engine; Acetylene torch with a small nozzle is best to pin-point.
Aside from the rubber sleeves on the intake runners, get new gaskets between the runners and the heads.

[kingbird6]

Guys, as a followup I replaced my Ox sensor, the distributor has been replaced and timing is set, checked CIS my control pressures warm and cold and they are good. No vaccum leaks found and it runs great warm and cold for the most part but...after a full warmup and run down the freeway she'll still surge under load a bit. Maybe mixture ? Seems to have plenty of power but a bit flat on the upper range. Still don't think I have a CAT problem though. I'm trying a new shop to see if they can locate the issue.

[DaddyGlenn]

Accumulator?