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Hello, I'm new on this forum and stumbled upon a new problem (or old) with my 2.5l 986 Boxster from 1997.

 

The problem occurs when the engine is started dead cold after sitting a few hours/overnight.

 

Engine starts immediately but the RPMs start to surge / hunt between 1100 and 700 RPM. This continues for about 10 seconds after which the idle smoothes out to the normal cold idle RPM. 

 

The first pull away requires a tad more throttle then normal to prevent stalling. After this first pull, everything is almost normal and engine performance becomes better and better. When the engine is hot, the idle sits at 780 RPM with a minor fluctuation now and then (seems to be more than normal)

 

I've been to two shops (official Porsche dealer and local Porsche specialist). Porsche dealer couldn't find anything and the specialist found the camshaft sensor on the left bank to be unplugged - but now comes the strange thing - the cabling is nowhere to be found!!!!!!? Took the car home to check myself but didn't find anything.

 

No camshaft related codes to be found in the diagnosis and no CEL either. 

 

Attached one pic showing the sensor and it's missing plug

 

Could someone help me out? - Is it possible for the engine not to throw a CEL when sensor is disconnected? - where is the sensor wire to be found?

20190205_174316.jpg

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It may be that the original engine is changed for some reason, the Euro cars, if i remember correctly, had only just one sensor on one camshaft. In this case it would therefore be normal that you can't find any wiring. Give the VIN and engine #, someone on the forum can compare the numbers for matching.

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Thanks for the quick reply. Do you know where I can find the engine number? I am able to locate the VIN

 

Also, can someone confirm that early euro cars only had one camshaft sensor installed?

 

Thanks in advance

Edited by Christiaan Poortman
Additional information/question

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1 hour ago, Christiaan Poortman said:

Thanks for the quick reply. Do you know where I can find the engine number? I am able to locate the VIN

 

Also, can someone confirm that early euro cars only had one camshaft sensor installed?

 

Thanks in advance

 

Just above the sump rail on the right side of the engine:

 

448430d1275597835-engine-number-stamp-en

 

RFM is correct on the single cam sensor.

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Thanks for the info. Will jack the car up tomorrow to clean up the engine number - it's a bit dirty right now.

 

Local Porsche specialist said that the car gave codes which could be related to the O2 sensors, but these aren't activated on a cold engine (as far as I know). Also, they measured the sensors and said they were all okay. Anything else could be giving the lack of power and hunting idle on cold start? 

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Have you tried cleaning your throttle body, MAF and idle stabilizer (if it has one)?

If you have access to Durametric and can get RKAT (or TRA) reading and FRA reading, those may give us more clues.

 

Also a good idea to check for intake air leak (by hooking up onto a smoke machine).

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Thanks for your reply. I'll sum up some things I've done:

TB cleaned

ICV cleaned (and checked, actuating freely)

AOS replaced

MAF sensor replaced (first thought this was the problem)

Spark plugs changed - old ones looked fine btw

Vacuum test was performed after all this and no leaks are observed.

 

Asked my specialist to give me the codes which were given.

 

Kind regards, hope you can help me further.

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Seems like you have gone through most suspects.

 

How about the ignition coils and fuel filter (if you have an inline one)?

What are the codes?

 

Next step is probably a Durametric scan to get more vitals. Then check the fuel pressure at cold start and after engine shut down (see if pressure holds). Possible you have leaky fuel injectors that upset the cold start fuel-air mixture. Another possibility is a sticky/leaky evap purge valve.

 

 

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Thanks for the reply. Asked the shop which code I had: P0130

 

They checked the O2 sensors and told me they gave a proper signal. 

 

Also, as I understood, O2 sensors don't affect the engine when they're cold.

 

Any explanation for this code?

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P0130 - Oxygen Sensor Ahead of Catalytic Converter (Cylinders 1 . 3) - Intercore Short Circuit or Limited Voltage Increase

 

Possible causes:

Crack in ceramic material - Oxygen sensor
Reference air polluted - Wiring harness
Short circuit in signal wire to sensor ground - DME control module 

(intercore short circuit).

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