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Old 01-24-2012, 04:43 AM   #1
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Engine issue

'99 boxster; 125k miles
Driving home on the interstate yesterday, I felt a rythmic deceleration...almost like I was tapping the brake, only it felt like the engine was pulling me back (similar to engine braking to control decent on a long hill). The rythm was about every 1-1.5 seconds. Rythm did not change as RPM channged, up or down. When I pulled off the road and let the car idle, the rpms would vary between 200 and 800...again, with a 1 second "rythm" to the variation. I was less than a mile from the house and made it home. No CEL. No fluid leaks. No noise (beyond the air intake matching the idle rythm). I didnt lose power and didnt feel like the car was struggling to drive. It never stalled. Thoughts on a potential cause? Am I safe to drive to the shop (10 miles; 4 Interstate)?

Thanks
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Old 01-24-2012, 05:50 AM   #2
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original fuel pump ?
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Old 01-24-2012, 05:52 AM   #3
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Originally Posted by milliemax View Post
original fuel pump ?
That or the filter would be my first guess too.
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Old 01-24-2012, 06:21 AM   #4
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Yes, its the original fuel pump. Would I be risking any major damage by driving to the shop? Would like to avoid a tow if possible.
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Old 01-24-2012, 07:30 AM   #5
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Originally Posted by luke1834 View Post
Yes, its the original fuel pump. Would I be risking any major damage by driving to the shop? Would like to avoid a tow if possible.
You can drive it.
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Old 01-24-2012, 09:18 AM   #6
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Thanks for the info. Drove it to the shop. Ran fine/normal for the first 4-5 miles and then the issue began again. Shop agreed (wihtout initiation) that a fuel pump/relay could be the issue...cutting in/out causing the symptom I was describing. Will hear back in a day or so.

Thanks again

Luke
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Old 01-24-2012, 09:27 AM   #7
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VDO fuel pump $216.95 Relay $18.69 relay location front fuse box. third row/third relay /Location 13

Last edited by milliemax; 01-24-2012 at 09:30 AM.
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Old 01-30-2012, 07:18 AM   #8
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Shop Response

Well...I feel like an idiot. After taking the car to my local indp. shop, the diagnosis was a faulty A/C Compressor. The compressor was kicking on/off rapidly once the pressure built to a certain point and would cause the "surging" effect while driving. It started to cause the engine to stall while at idle while the mechanic was testing it. Shop quoted $1100 to replace the compressor...im thinking about DIY and will be waiting until the weather warms a bit. Anyone tried this particular job?

Driving the car (without the compressor and with the refrigerant removed) and it runs great once more...

Thanks for the helpful tips
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Old 01-30-2012, 12:15 PM   #9
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Luke thanks for following up and lettting us know the cause (some posts leave us all hanging without an outcome!).

I have to say that the A/C was not one of my top five potential problems - learn something new here everyday.
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