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Viking66 · 09-27-2020, 02:00 PM

Hi all,

I have a 98 986 2.5 that needed an engine change..locked up. So I replaced it with a 1997 2.5 with 41K on it. That said. After being very hard to start the car will idle, but not to well. I have a Foxwell tool with the Porsche SW and the Actual Values show between 28-30 for the MAF reading, and 5.2-5.5 ms for the injector time at 800 RPM idle. According to the manual, they should be half that for both. If I pull the vacuum hose from the Tank vent valve it idles great because it gets the additional air it needs for all the gas the DME is pushing into it. If I do not pull that hose the car will start to pop after a bit because of all the extra fuel.

I have tried 3 different MAF units and all the same. The readings do change when the RPMs are raised so I can see the MAFs are working.

I sent my DME, Immobilizer and Key to ECU Dr and they told me my units are fine...worked perfect on their test bench and test car, has to be on the car somewhere.

I am about to pull the last hair out of my already bald head trying to figure this out.

Any help or ideas would be helpful.. Thanks in advance!!!

09-27-2020, 02:00 PM	#1
Viking66 Registered User Join Date: Jun 2020 Location: Louisiana Posts: 7	1998 986 High MAF readings Hi all, I have a 98 986 2.5 that needed an engine change..locked up. So I replaced it with a 1997 2.5 with 41K on it. That said. After being very hard to start the car will idle, but not to well. I have a Foxwell tool with the Porsche SW and the Actual Values show between 28-30 for the MAF reading, and 5.2-5.5 ms for the injector time at 800 RPM idle. According to the manual, they should be half that for both. If I pull the vacuum hose from the Tank vent valve it idles great because it gets the additional air it needs for all the gas the DME is pushing into it. If I do not pull that hose the car will start to pop after a bit because of all the extra fuel. I have tried 3 different MAF units and all the same. The readings do change when the RPMs are raised so I can see the MAFs are working. I sent my DME, Immobilizer and Key to ECU Dr and they told me my units are fine...worked perfect on their test bench and test car, has to be on the car somewhere. I am about to pull the last hair out of my already bald head trying to figure this out. Any help or ideas would be helpful.. Thanks in advance!!!