Hello everyone. I have 1985 928s(Silver/body kit)
I get this R.P.M. surge.. The R.P.M.'s go from 650 to 1500 and then back down. I have replaced the hot-wire, new plugs and cables. With no luck. I was told that it could be the LH Brain. I would appreciate any help on this issue. I have found 2 at a reasonable price before I purchase it maybe there is something else that could be a quick,and easier on my wallet. Thank you for your time and concern on this topic.

 

Have you checked for vacuum leaks James? Do that before investing in a new brain.

Look at all the vacuum lines leading from the brake booster and check the one-way vacuum valve there as well.

Post some pics of your car - it sounds purdy.

 

Yes, I had someone look at the vacuum lines. It seems to constantly boil down to the LH Brain. I hope it works. I will have just enough money to purchase both the brains this week.

I will post some pic's of my car as soon as I get my digital camera back. Thanks for your help. Is you avator a pic of yours? If so, how much for a conversion like that.

 

Searching the Archive came up with this discussion on 'surging':

<a href="http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=14&t=000376" target="_blank">http://forums.rennlist.com/forums/ultimatebb.php?ubb=get_topic&f=14&t=000376</a>

Yep, it's my little chop-top James. Would you believe $25K plus the donor car - 10 years ago. The PO commissioned the work.

 

Hi James,

I had the exact same thing on my '89 S4. The Porsche guys blamed it on the LH computer, because there was a faillure message in the computer. Do you also have the problem of stalling after revving? It turned out to be (after a tip of Greg Nichols: <a href="http://ourworld.compuserve.com/homepages/nichols/tip443.htm)the" target="_blank">http://ourworld.compuserve.com/homepages/nichols/tip443.htm)the</a> idle stabilizer.
In my case it could also have been the LH computer acting up triggered by the idle stabilizer or something, but the trick worked for me. If you need more detailed info, mail me.

 

I will look into the idle stabilizer and try to find the link above to the tip site. I think I have been there before. Thanks again.

 

One more thing after reading the past posts. I have no cats and no resinator on it.This I cut out when I first bought it 6 months ago. I was told I had really bad clogged cats. I still experienced the idle reving then dieing. I does happen if I hold the gas on a quarter of the way and wait 2 seconds and then come the stall. I appreciate all the responses.

 

Okay... once againg thanks for all the info and help. I have decided to take it to a shop on the 1st of May. I will keep you guys posted on what it was that was causing the surging.