Intermittent problem

[Porsche 935]

About a year ago I bought an 84 Carrera for a nice driver car. Many things were neglected. Worked out the rich fuel condition I discovered when I installed a wideband o2 in the car. Some aftermarket chip. I know the coil and sensors were replaced, also dme replay. Also air leaks were fixed with new gaskets and boot. Issue is sometimes car pulls really well from low rpm to redline. Other times, it stumbles as if rich or lean and then takes off like a boosted car. The wideband does not show a rich or lean condition so tracking down the culprit has been difficult. Any suggestions?

[Porsche 935]

Not even a guess?

[Chuck.H]

search the forum for bad tracks on the AFM - I know some have had problems with the wiper wearing grooves in the resistive surface over time. Depending on how it comes and goes may give you more clues... does it always START and IDLE perfectly?

Chuck.H
'89 TurboLookTarga, 423k miles

[Porsche 935]

Always starts and idles perfectly. It only happens at low rpm, trying to accelerate.

[DRACO A5OG]

+1 Check the AFM arm by testing the voltage output with a 9volt battery. a 944 fella on youtube shows how to do it.

Also check the Dizzy, put the car to TDC and pull the dizzy out and check for radial slop, The dizzy should have some play horizontally but only 0.5MM, if more than you need to rebuild the shims to get that tolerance. Just imagine how the rotor spins and if it has too much slop how it will not make full contact with cap ignition points.

If you remove it, spin it, if you hear a buzz, than the internal snap in bearings are gone. Then the Dizzy is pretty much toast.

[Porsche 935]

I decided to get serious about this issue. Tested all the sensors, checked fuel pressure and injectors, pulled cap-rotor and wires and ohmed. Adjusted valves and refurbished air flow meter, still same problem. Smoke tested manifold- no leaks. Used mirror to check all vacuum lines, noticed slight crack in hose that was crimped onto copper tube leading to intake boot. Removed and pulled vacuum on it. Tested good but then slightly flexed hose and lost vacuum. Retested,same thing. Cut hose off and replaced with another piece of hose for now and no more leak. Reinstalled on car, runs perfect now. Problem found, I guess when engine torqued to engage clutch, hose would leak. Now just looking for factory replacement hose.

[Porsche 935]

Found part online, can not believe the want $200 for it and no one sells just the reducer hose. Anyone find alternative to the hose section?

[DRACO A5OG]

That is a common leak, most if not all just do the thing you did and call it a day.

[Quicksilver]

Originally Posted by Porsche 935

Found part online, can not believe the want $200 for it and no one sells just the reducer hose. Anyone find alternative to the hose section?

Same hose was cracked on mine during the "Rubber Explosion®" incident. Stupid quantity of money to replace the whole hose assembly. I got the correct size of hose for the large end and then a smaller hose that could be forced inside the smaller end. Hose clamp it on and you are done for a couple bucks.