View Single Post
Wayne 962 Wayne 962 is offline
Author of "101 Projects"
Wayne 962's Avatar
Frustrating 959 Problem -> Need suggestions...

Okay, let me start by saying that I am aware of the proper diagnosis procedure for the engine, and it's quite involved. I'm hoping to get some ideas on what could be the problem with the system before I start from step zero and check *everything*.

Here's the problem. When we came back from SEMA, I took Tom Woodford (the fellow who helped me write the Engine Rebuild Book) out for a drive in the 959. I drove first, and then I let him drive. Before I let him drive, I noticed that the gas tank level was low, so we filled up with some 91 octane at the local Chevron (this station closed for "maintenance" a few days later). After about 2-3 miles of driving, we got back to the shop, and the car stalled as I was putting it away.

Next time we took the car out, it wouldn't start without feathering the gas, and giving it a little bit of throttle when starting it up. It's been the same way ever since. Here are some more details:

- I ran the tank down to 1/2 full, then filled up again with 91, and then some 100 octane from Willow. I also added some of the Swepco fuel system cleaner that we sell. So far this has had no effect.

- The car ran pretty fast at Willow - the car has plenty of power, particularly at the top end. If there is a power loss at the top end, it's news to me.

- When you let off of the throttle and let the clutch out (pedal in), the engine rpm drops really, really low, and then bounces up to about 900 or so. Occassionally, the car stalls if the idle gets too low, and particularly if the car is cold. This dropping down below normal idle happens 100% of the time since this problem started.

- I have swapped out and replaced the idle control valve (ICV) with 2 other ones, and this has no effect on fixing the problem.

- The fuel injection system is not showing any fault codes. This in particular is odd because I did run the car briefly without the ICV hooked up (it ran worse). I would have thought that this would have tripped a fault code. Maybe it has to run for a certain length of time before the code would have been tripped.

- No obvious vacuum leaks, although I have not yet put my vacuum gauge on there to check (that will probably come tomorrow). Still, I doubt that there are any leaks because the upper operating range seems good, and the boost levels are good as well.

- The car runs very rough at cold idle, and if you get on the throttle, you can hear it missing when you rev it to about 2000 rpm. When warm, the car seems to have lots of power. When the car is warm and idling, the idle seems to miss slightly (much less apparent than when cold).

- Oil cap on tight.

It may be a clogged injector from grime in the bottom of the tank, but that doesn't seem likely to me either. I will replace the fuel filter regardless (ordered one today - it's the same as the 928). I don't really think it's a temperature sensor, because the engine runs rough at warm too.

Any thoughts from outside the box? I have a gut feeling, it's something real simple, instead of something real complex...

Wayne R. Dempsey, Founder, Pelican Parts Inc., and Author of:
101 Projects for Your BMW 3-Series 101 Projects for Your Porsche 911 How to Rebuild & Modify Porsche 911 Engines 101 Projects for Your Porsche Boxster & Cayman 101 Projects for Your Porsche 996 / 997 SPEED READ: Porsche 911 (October 2018)

Check out our new site: Dempsey Motorsports
Old 11-26-2007, 05:12 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)