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Jeff NJ Jeff NJ is offline
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Join Date: Nov 2013
Location: NW NJ
Posts: 1,187
So when you say a few seconds before it jumps to 850 rpm, is it literally that, or longer? I took a pic of my pierburg switch and the vac line from the disto goes to the top plug and the vac line going to the TB comes from the plug directly under the electrical connector. The rear plug is what vents to atmosphere.

If you put a timing light on, it is obvious when it is working and the timing changes it makes. For my car, it is about 5 deg BTDC until the switch turns off and it retards to about 5 ATDC, so it is easy to see. About a minute after cold start, the 35C temp switch turns off the Pierburg circuit and the timing retards and the rpm noticeably drops.

Your issue doesn't sound like lean AFR, but to get a cold start AFR, I unplug the WUR connector and the AFR doesn't really change much if at all by the time the AFR gauge can get a good reading, since there isn't time for the environment to heat up the WUR element to change the fuel pressure.
1988 930 Venetian Blue
Old 04-25-2017, 07:31 PM
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