speedster959

Been having some problems with a rough idle on start-up, took my 75 911 Carrera to the local factory trained mechanic and he found that the pressure from the warm-up regulator is not reaching 5 barr in 5 minutes (from a cold start)but only barely 3 barr. He did a "knock" adjustment and it helped a bit, up to nearly 4 barr but still not reaching correct pressure according to him.
My first question is what should the pressure be after 5 minutes? Second are warm-up regulators interchangeable from year to year. My factory manual lists the warm-up regulator for a 75 as Bosch part number: 0438 140 001 or 0438 140 008 or 0438 140 008, would a Bosch part number 0438 140 011 work in a 75 911 Carrera? I found a great price at a wholesaler closing out old stock. Any help would be great, thank you in advance.

Jeff Curtis

David, it all boils down to the final control pressure when warm, and it should NOT take five minutes, more like a minute, maybe two?

Have you looked at the auxilary air regulator that allows extra air in the intake upon startup and once it gets heated up by the 12v supply, the extra air shuts off...lowering your idle??

If your control pressure doesn't get up to 5bar, then that means your car is running rich, due to a lower pressure on the piston in the fuel dist.

So, I think you may be on the right track, as usual, check for vacuum leaks, etc. as well.

As for using another WUR, try the "knock" adjustment again to see if you can raise it a bit more, some people tap out that access hole and put a 6mm bolt (10mm head) in there with a locknut so it's adjustable.

I did NOT perform this "mod" on my SC, but it seems like it would be feasible.

speedster959

Jeff thanks for the advice. I read the article on making the WUR adjustable and I might have to try that but sounds like a winter project just in case things go bad with the modification. My mechanic was measuring the pressure right off of the WUR and he must have been looking at the final system pressure after the 5-minute warm-up period. He also adjusted the mixture to tried and achieve the right CO content but it was still a little high and floating. I’m not sure if he checked the auxiliary air regulator, I would assume that he would have, most of the members in the local PCA consider this guy a Doctor not just a mechanic, he came VERY highly recommended. I’ll have to do some reading on the auxiliary air regulator and see how it plays and how to test it.

Do you know the answer to my second question regarding the part number for the WUR and if the 011 will work in my 75?

Being a new Porsche owner I sure appriciate all the help. THANKS!