My 75 1.8 is inconsistent in its idle. It will idle at 900rpm but often at a stop light it will idle at 1800rmp. Idle will either be 1900 or 900. All of the hoses and seals are good. Vacume is at 16

I changed the air flow meter to a rebuilt one in hopes to solve this problem. The new unit would only idle at about 600 and Idle would not adjust. So I put the old one back on.

Why does it run better with the old unit??

How do I solve the idle problem??

1,8 idle problems are almost always air leaks. check the connections at all the hoses and the *2* O-rings at the oil filler.

there are any number of reason why the rebuilt one isn't as good as the original ...

Pull decel valve and plug all the vacume lines from it. Not needed and causes air leaks. I have 1.8 that idled odd and that fixed it.

there are any number of reason why the rebuilt one isn't as good as the original ...


So what are some of those reasons??

So how important is is the deceleration valve?? I can't find any vacume leaks anywhere.

unavailability of proper repair parts, lack of skill and understanding on the part of 'technicians' performing the work, original design that does not lend itself to "rebuilding." (lots of Bosch parts have little provision for refurbishment; standard service is replacement.)

the decel valve is an emissions band-aid, designed to provide extra air during overrun to reduce unburned hydrocarbon count. like a lot of these devices, they're good at doing what they're supposed to when they work right, but they have many undesirable and hard-to-pinpoint side effects when they start wearing out.

even in 1970, Porsche had been building cars just over 20 years, and they never expected the cars would remain in service, especially daily-driver service, for more than 35 years...

what have you been using to check for vacuum leaks?

So I pulled the decel valve and pluged the line.

It works great.

I had changed all the hoses and seals so I assumed that I didn't have any leaks. Still apears to be true.

Thanks for the help.