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CEL + car shuddering, problem, possible P0740?

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On my 2000 S Boxster with 62k miles, 60k service done at indep shop.

Currently my CEL is on, and my car shudders a lot when on. When the throttle is pressed, the sound of the engine somewhat alternates and isn't really locked on at a given frequency (think of a Mustang GT's engine sound which kinda pulsates). The car also shudders, and there is a wierd pulsating sound coming from the exhaust.

This is the 2nd time I've had this problem:

Yesterday as I was driving from SF to Palo Alto (after the car was warm) I started to have the CEL blink sometimes when the RPM went over 5k RPM. By the time I got to Palo Alto, the CEL was constant on, and by the time I got to the local roads I could feel the symptoms described above.

The first time this happened (about 2 weeks ago) I just drove a few miles locally the next day and the symptoms dissapeared and the CEL went away a few miles after that. I brought it in to the indep shop and it was diagnosed with the Porsche Scanner. I don't recall the exact codes, but the mechanic did mention something about the torque converter/auto transmission. I did a search on these forums and it looks like the closest thing is this code: P0740.

Does anybody know what could possibly be wrong, how much it might cost, and what I should do?

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Does anybody know what could possibly be wrong, how much it might cost, and what I should do?

Well the first thing to do is take it to autozone and have them pull the exact codes (it's a free service they provide). I think if the light is blinking it means there is something seriously wrong and you should get it checked out asap... I could be wrong though, check the manual.

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Took it to streetwerke, diagnosed as:

Engine Misfire

P0740 Automatic transmission problem

a bunch of O2 codes

Took it to modderman:

Mechanic said engine spark plug was most likely due to the torque converter locking and unlocking.

They're taking a look now, we'll see whats wrong with the tranny

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