Idle issue solved!

[davidpsalt]

85 Carrera - 3.2 ... Issue began as a miss while driving. Then would idle rough at start up then mis while driving. Then over time began stalling. So, I initially inspected my Cyl Head temp sensor, and the reference and speed sensors - the wire insulation was crumbling away so I ordered all three sensors. Installed them but they did not fix my issues. I then bought the Bentley Manual and began reading how the Bosche Fuel / IGN system works and started hunting for vacuum leaks. They were everywhere. So, I ordered new rubber lines - vacuum to Fuel Reg, and to fuel damper (two small 70 degree rubber hoses), hard pipe behind intake manifold with rubber end that had a big crack in it (it connects to the rubber intake boot), two large rubber hoses from my oil tank to the crank case and intake boot, another smaller hose from intake boot to the oil tank. Replaced the boot from the intake to the Air Fuel Meter, bought a reconditioned Air Fuel Meter (sent my core back) and Idle Control valve and new hoses for Idle control valve. Also replaced the idle adjustment screw with O ring.

Sure - I threw lots of parts at it but all the rubber was hard, cracked and allowing more and more “un metered” air into the system. All of it was 37 years old - and I want it to go another 37 years.

Fired it up and all problems are solved. Idles great, no miss, runs great! Hope this might help others that are chasing down vacuum leaks and idle issues.

I may still end up dropping the motor/trans and do a top end rebuild over the winter - but felt I needed to resolve this before hand - now I can get some fall trips up to the North Georgia mountains and twisty's before doing so!

[carreradpt]

Dave did you order the rubber parts as a kit? Or singly? Do you have the part numbers handy for the replaced parts?

[davidpsalt]

Hi Dan - I had to buy them individually. The pricing varied across all retailers I looked up - our sponsor, Sunset Porsche, Atlanta Auto, Vertex, etc. Some parts I used OEM Porsche parts - i.e. the Intake manifold 90 degree rubber boot that connect the intake to the AFM. The two large hoses that run from the oil tank to the crank case and intake boot were URO. The smaller hose that runs from the oil tank to the intake boot was Porsche as others didn't have it. These three lines were hard as a rock and cracked - glad I replaced them. My biggest leak was on the hard line - I believe it is a copper pipe that runs from the intake boot over to the drivers side behind the heater fan - its a copper tube that has a small rubber connection to a venturi valve (could have the name wrong) - it had a large crack. I believe that over time as "un metered air" was getting into the system the Bosch Fuel injection would adjust rich/lean to the best it could - as well as previous mechanics adjusting the idle, etc. Eventually, as more cracks let more un metered air in it could not compensate with the data it was getting from the AFM, O2 sensor, etc. My logic in replacing all the rubber hoses was based on my desire to make my car extremely reliable and enjoyable for years to come. Great DIY project that I cold do over a couple weeks at night in my garage - keeping the costs down to only parts.

Regarding part numbers - I ended up finding a European parts site that had the porsche schematics with the part numbers listed below - this was awesome - I could match up the hoses I wanted to replace with the correct part numbers - then I googled those part numbers and found the best prices locally.

Feel free to IM me and i would be happy to discuss as I learned alot and there is too much to type here!

[carreradpt]

Thanks Dave. I have been doing the same just to head off vacuum issues. A piece here, a piece there. Glad you got it solved.