mnotz

Hello!

So after I have run through the posts that even somewhat apply to the issues with my '80 and running through some troubleshooting steps I could think of (check vacuum connections, electrical connections to sensors, etc.) I feel like I should consult the resident wealth of knowledge here

I have no idea how the car ran before the intake refresh, because the intake was in pieces when I got it. Pretty much replaced all vacuum lines along with a TB/WP job (issues were present already before the TB/WP was done). Here is what's happening:

Cold start - car idles at around 1,500rpm for 30 seconds, then begins to surge in about 1-1.5sec intervals between 1,000rpm and 1,700rpm for about 90 seconds. After that the idle will settle at around 1,200rpm and will stay there steady for as long as the engine runs.

Warm/Hot start: Car starts and immediately settles at 1,200rpms, no surging.

Aside from that, the car runs very well and has lots of power throughout the rpm range.

The adjustment screw in the front of the throttle body is all the way in. Backing it out will increase the idle further. Pulling vacuum off the distributor will drop the idle to about 1,000rpm. Engine is timed spot on. Another thing I realized - while it's doing it's minute or so of surging, if I turn on the A/C, it will go into a high idle right away. Must have something to do with the idle increase for that circumstance.

Anyone that can give me a few more things to check? I have access to plenty of (used) parts in my personal 928 parts room


Thanks to all of you already in advance,
--Marcus

granprixweiss928

My first guess....vacuum leak.

mnotz

Yes, that was kind of my thought too. I could have access to a smoker next weekend. Pressurized smoke, through the AFM should do the trick, no?

What I am really worried about are the A/C solenoids and attached lines - the electrical in this car was a nightmare. I pulled left overs from 3 different alarm systems and cables for a pretty massive audio install which left everything behind the center console looking like a war zone. I brought pretty much everything back to stock and gave the vacuum lines a visual but not anything more.

mnotz

For some reason the last message posted twice...sorry for that!

checkmate1996

I'm guessing vacuum leak too. One clue is when you mentioned the AC kicking on the idle went up. Well, that little do hickey on the cross bar in the engine adds air to the system to help from stalling.

I solved all my vacuum issues when I ditched all that old german rubber hose and when silicon. Never looked back. Pull your air box and tubes and check all of the end of your vacuum lines for physical wear. Then get a vacuum gauge and hook up to your lines to see where you leak is.

mnotz

That sounds like my approach to take, checkmate! Thanks! However, no dohicky on my '80 (or the '81) on the bar. Both of my '86.5 do have it though. Not sure how the extra air is delivered when A/C is turned on on the other two...