1983 928S 5Speed Idle Surging?
 

i have 1983 porsche 928s 5speed with a idle surging at start up the rpm go up and down from 650 to 1800 even when it warms up its still the same. the car drive fine when you are in gear driving around. so far i replaced the spark plugs, checked/fix vacuum lines, replaced both orings on the throttle body. anyone have ideas what it could be? thanks

If the car is new to you, could be a long list. Previous owners are known for compensating instead of fixing many things. Once you have all the vacuum leaks chased down, then I would start looking at vacuum hoses hooked up to the wrong place, and hoses that might be blocked. The O rings on my 83 fuel injectors leaked so bad that the idle speed needed to be turned down 100's of rpm after they were replaced, but the old ones didn't have any special symptoms otherwise.

"Jim Morehouse" jim928@ptd.net has the WorkShop Manuals on a CD, and you will need them if you plan to work on the 928 yourself.

Sorry I can't suggest anything more specific. I tried a couple simple searches, and kept getting stuff related to problems on 32v cars. Running rich is often associated with surging, so you might want to think about electrical connections on sensors as well, the air flow meter and O2 sensors etc.

how can you tell if air flow meter is bad? i know i can get a rebuild one for $206

I'm not suggesting its bad, just maybe a poor connection. I believe you can measure a voltage output that should vary with flow at the connector, but I don't know the pin or details.

This list is a "little" slow, but answers show up in a day or so that will be better than mine.

Hi try this http://www.pca.org/tech/tech_qa_question.asp?id={68B4EF0E-AEC5-4444-BDB2-1F8C292FCF0B} and watch this site for down loads when it reactivates http://www.cannell.co.uk/Manuals.htm

Here's some good information

There are several possible causes for the surging.

- An owner of an early car says:
Does your engine have a vacuum limiter? It's a saucer shaped thing on the US passenger side of the throttle body. Has two large hoses on the throttle body side, and one small hose on the outside.

It can become overly sensitive with age, and it will give the variable idle symptoms you describe.

You can replace it with 5/8" and 3/4" rubber heater hose blockoff caps, without any problem. Porsche stopped installing them in 83 or 84.
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Vacuum leaks in general can cause surging. Use a four-foot piece of rubber or plastic hose stuck in your best ear to try to locate any hisses. Stay out of the moving parts!

The Temp II sensor, on the top front of the engine can cause problems if it is saying that the engine is cold after it warms up.

Improper ignition timing can cause surging.

If you do not have the Factory Workshop Manuals, it will be very difficult to maintain the 928. Contact Jim Morehouse and buy the complete set of 928 tech info CDs that he has prepared. Jim had every scrap of 928 info that he could buy or borrow professionally scanned, converted to pdf files and burned to CDs. There is a HUGE amount of info in the set - this will be the best money that you will ever spend on your 928. Jim's email is jim928@ptd.net (We have no commercial connection with Jim.)

jsbc, thanks for stopping by, that UK link is sweat.

The UK manuals are what I suggest as last resort, shuts down when that months bandwidth is used up, and the images are from microfiche (I think) and too fuzzy for regular use. They are of course 100% better than nothing, or the poor mans manual, Pet6. ;)