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Joined: 29 May 2013
Posts: 20
Location: East Yorkshire

PostPosted: Sat Mar 23, 2019 7:12 am    Post subject: Rpm sensor, difficult hot start Reply with quote

Morning. I am having a couple of issues at the moment.
Firstly the car won't accelerate past 4500 rpm. It is like a rev limiter comes on. Pulls fine up to there. Same in every gear. I found an old thread on another site with exactly the same description. He found a loose wire on an RPM SENSOR. I guess this is different to the crankshaft sensor. Does anybody know its location?

Second issue. Car starts fine when cold but struggles to catch when warm. Had one back fire when staying after a couple of hours.

The car is a 3.6 2002 tip
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Joined: 21 Mar 2015
Posts: 7726
Location: Brighton

PostPosted: Sat Mar 23, 2019 7:21 pm    Post subject: Reply with quote

Rpm sensor is the Crank Angle Sensor , n/s/r and not very accessible on a tip , The bolt can rust and the sensor can corrode in but with tips its tends not to as its a bit better protected .

Ok .. what i think .. 2 seperate things actually ..

A CPS fault .. car starts when cold but will not start .. no back fire nothing when hot .. leave it to cool down and it will be fine until hot again .

A back fire indicates a timing or a mixture problem .. a cps wont send a signal so the car will NOT fire spark or fuel .. hence it cant back fire ..

Therefore im thinking its not the CPS .. it can be but logically working from what you have said then it doesn't fit the normal fault pattern for one of these .

Now if this was a Boxster i would be saying 100% i know what it is but on a 996 this is a bit more unusual ..

Basically a typical Maf fault on a Boxster and it will NOT rev above 4500 rpm .. we unplug the maf then road test it to confirm it will run normally then we replace it .

You can do the same on your car , unplug the maf then start the car .. it wont be happy at first but it will drop to default values .. then drive the car and see what difference it makes .

I WILL say i have a tester to clear fault codes as there will be some after this .. it WILL run funny when unplugged and indeed when plugged back in again until the car adapts .. but it will also prove its the maf or not .

Maf = Mass Air Flow Sensor btw .

Up To you if you want to try this or get a garage to look at it though .. this is just what i would be checking .


Just to add .. if you get the car hot when this fault happens then plug a noid light into an injector you will see if it triggers or not .. its a base indication of a working or non working CPS.

The only other way is to scope the signal or replace it regardless to prove its ok .
My Daughter's Crowdfunding has hit the target .

Thank you all so Very much .

She's not going until july 2020 though .


7pm - 9pm

Indy Mechanic .
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Joined: 29 May 2013
Posts: 20
Location: East Yorkshire

PostPosted: Sun Mar 24, 2019 7:39 am    Post subject: Reply with quote

Thanks for the reply. I was thinking along the lines of the maf sensor. I was thrown by the other post I found talking about a loose plug and an rpm sensor.
I have just bought a cheap code reader that cancels codes on my corsa. Not sure if it will on the porsche. I haven't plugged it in yet.
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Joined: 29 May 2013
Posts: 20
Location: East Yorkshire

PostPosted: Wed Apr 03, 2019 6:16 am    Post subject: Reply with quote

Just to let anybody know for future reference. The fault turned out to be crankshaft sensor. New one fitted and it was away. 😊
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Joined: 12 Apr 2019
Posts: 1

PostPosted: Fri Apr 12, 2019 6:04 pm    Post subject: Reply with quote

Hi...in my case the crankshaft sensors both give steady measurements, both in resistance cold and warm as in AC voltage while starting.
There is on one bank a camshaft sensor on which i can't get a descent reading. Has anyone got more information on this sensor/or the ignition system or are there other things known to cause this?
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