Car will not idle, frustration builds!

[84Carrera911]

Alright I'm stumped on this one, hopefully someone can help me out, here's the story:

My Porsche 911 Carrera 3.2 recently had a rebuilt transmission installed about three months ago, and had been working great. I drove it 400 miles from PA to NC with no problems. I had no problems for a few weeks while driving it in NC. The only issue I noticed with the car is that acceleration has recently been a little bucky/surgey. After washing the car once, the Clewett Engineering plug wires were arcing badly and it was running on only a few cylinders very roughly. After letting it dry, however, the issue went away. Also, idle has always been kind of rough in the car, but that's the way I've always remembered it.

The real problems began when I was driving it home one day, gas light had just come on, and I was about a half mile from my house, rounding a corner coming down a hill. I decided to open up the throttle a bit through second gear, and shifted at about 5500 rpm into third. Once it was in third and I reapplied the throttle, rpms just began to drop, as if the motor had no fuel and had run empty on gas. While cursing myself for driving aggressively with low fuel I pulled it over, a few hundred yards from my driveway. I attempted to restart the motor, but with no luck, as it seemed to have run empty on gas.

I drove my buddy's truck to a local gas station to pick up 5 gallons of 93 octane, and I filled the porsche up. Still no signs of starting, just a few occasional pops.

I got the car towed into my driveway and began to look it over. I found that my coil to distributor plug wire had broken on the metal end, the metal breaking in half. However, I don't know if this was the cause of the problem, as the arc probably could have jumped the small gap over the break in the metal. However, I replaced the wire with a generic universal wire from Advance Auto. I also found a white plug/sensor wire that had come disconnected from a cluster of three plugs that are located on a rail in the upper left half of the engine compartment. The wire was a single white wire that came off the plug.

After fixing these two issues, the car was able to turn over and tried to idle, with signs of a healthy stable idle at 800 rpm, but an occasional miss that would drop rpms and almost stall the motor, followed by a surge to 1200 rpm, then another drop until it eventually stalled itself out. This led me to believe it could be a fuel issue.

I replaced the common relay that fails next to the ECM under the drivers seat, hearing that this was a common issue. This made no difference.

I replaced the fuel filter, no difference.

I began to suspect the fuel pump, so tested idling fuel pressure at the rail: 35 psi, with a small vibration/fluctuation in the guage of 2-3 psi when the motor misses. So I assume the fuel pump is ok, but I know that there is still a chance that it is weak.

I checked for vacuum leaks and I can't find any, cap and rotor seem to be in good shape, replaced 5k ago.

I checked spark at a plug and it looks strong, which I expected since it will idle, just not well.

The motor makes a choking sound right when it decides to quit.

I'm in serious need of some suggestions.


Thanks!!

[Porsche_monkey]

Bucking/surging = lean

no idle = lean (maybe)

I am guessing you have a vacuum leak.

[steely]

Broken 'white' wire at 'cluster' = CHT?

Am guessing you may be describing the Cylinder Head Temperature sensor - and I think if it opens, the DME is misled into thinking you are overheating.

Or, it could be your O2 sensor, and that might just affect idle.

on edit, ah but you said you fixed that (never mind).

I'm leaning away from fuel and suspecting interrupted spark due to flywheel sensor probs.
Maybe they were disturbed when you repaired the CHT wire at the cluster. just a theory.

[avi8torny]

+1 on the head temp sensor. Had this happen a few years ago.

[Larrybrook]

Read teh link below, another pelicanite hat problems with idle and it turned otu to be the oil cap seal.

The $2.25 fix!


Larrybrook

[Larrybrook]

whoh...next time I'll do a spell check...sheesh...

[84Carrera911]

I tested the CHT sensor and I got a reading of 3k ohms. Supposedly its supposed to be in the 1-2k ohm range, will this cause that much of a problem? I think I will use a variable resistor set to 1.5k ohms hooked up to the sensor lead and see if it will run with that. Thanks

[84Carrera911]

Ok, I don't think its the CHT sensor. I found a vacuum tube that was disconnected, from the air valve (above the oil fill cap) to the temp sensor that is right behind the throttle body. Now that it is reconnected, I can rev the motor to about 3k rpm, but it is still sputtering, occasionally popping with light backfires, and smoke is bluish white out the exhaust. This is making me still think it could be a fuel issue.


What fuel pressures should I be seeing? Apparently the stock fuel pump is rated at 58psi according to the NAPA guy, should I be seeing this at idle? What should the fuel pressure be doing from 2-3k rpm?

I'm suspecting that the screen in the fuel pump may be clogged from sucking up gunk in the tank. So I think that may be my next step, but I want to know what fuel pressures I should be seeing before I dive into that mess.

Thanks

[mackskibum]

Did you mess with base idle speed? Base idle out of adjustment can cause the idle bounce you describe as the ICV tries to maintain set RPM.