Engine rhythmically cutting out

[63buglover]

I have a '97 Boxster, with the base engine & 5 speed transmission. I have done several things to it in the past year attempting to fix missing/rough running issues; replaced the plugs, all the coil packs, MAF sensor, and the 2 front O2 sensors. Ran great for a few days this last time (one of the new coil packs went bad; reinstalled one of the old ones that I was pretty certain was still good and reset the ECU by disconnecting the battery).

Now it has started doing something completely different; it has never done this before.... you can hold the RPM's at a steady 2k for instance, and the engine will rhythmically cut out for just a moment, just as if you had turned the engine off and then back on.... on, off, on, off, on, off and so on. The dash stays the same however, other than the RPM gauge following the revs. It started doing this for a few minutes (embarrassing when driving thru town), then stop, and then do it again the next day and stop, but now the issue seems here to stay. So far it hasn’t thrown a CEL.

I sure would love to be able to drive it and enjoy being topless before the snow flies... any ideas?

[JFP in PA]

Start by checking your fuel pressure and delivery rates, and when was the last time you changed the fuel filter on the car? Another possibility is a crank position sensor on the way out.

[63buglover]

I have no idea when the fuel filter was changed, I just bought it nearly 2 years ago now, I guess. That is something I oughta do, anyway. It's so rhythmic that I can't really see it being a fuel filter, but could be the fuel pump going on/off I guess. It may be the crank sensor … but I’m worried it may be the ECU doing it, since it is so well timed & repeated. It may be turning the coil pack feeds off, turning off the fuel injectors or any number of things… either by itself or as a result of a faulty input.

It will be fun to track down. Maybe it’s a good excuse to buy a Durametric analyzer?...lol