I am new to Porsche ownership. Going on a week now. I picked up a 1986 non turbo 5 spd. Car runs and has had about 4800 dollars worth of work done in the last 12 months (documented) timing belts etc. Power windows work, power mirrors work, a/c works, sunroof works, power seat works. Generally great shape just one issue. (at the moment) all gauges but the gas gauge working as well.

The car starts immediately, It is however idling rough below say 2200 and falls a bit flat on power above 3000 rpm. I have been doing lots of small things and followed all the vacuum lines, i removed the AFM tested it with a 9v battery and cleaned both contacts (on the arm and the strip in addition moved the arm so it now swipes on fresh contact are.

Results, no change. Still have the issue. Any thoughts on hat to try next? Thanks so much for any direction anyone can provide! Thanks!

 

It could be the TPS...check the throat of the throttle body and make certain that the scum ring behind the throttle blade is gone, check out the movement and cleanliness of the TPS unit as much as possible. Dirt & corrosion can be so troublesome if you don't catch it early on..Sounds like a great car though..Enjoy!

 

Rough idle in our cars is usually (ordered most likely to least likely, re-order as you see fit based on work already done recently):

- bad motor mounts
- balance shafts timing off by a tooth... especially likely if it just had a belt job done recently.
- misfire due to cap/rotor, plugs, TPS idle position, AFM, FPR, etc.

Can you tell that it's low on power over 3000 relative to a different NA 944? It may be fuel pressure related (running too rich or lean). That can also affect idle, under the misfire category.

Also one note... the late cars (which includes 1986) use an AFM that uses a ~5v regulated reference voltage. The early DME used ~12v (unregulated) with an 8v minimum, so the 9v battery trick is really only applicable to the early AFM unless you wire in some other known voltage drop. I would wire some 1.5v batteries in series until you find a combination that gives you somewhere between 4.5v and 5.5v, one battery may need to be somewhat used up.

 

Welcome to Porsche ownership and their problems. A great place for maintenance help is at Clark's Garage.com and makes for great reading.

http://clarks-garage.com/shop-manual...ure-index4.htm

Cheers,
Larry

 

Thank you so much for your replies guys, I will be doing all of the recommendations you have posted this weekend and will post results.

Thanks for the welcome as well! I am a muscle car guy and come from that arena but always wanted a Porsche. Could not pass on this one for the price, I was looking for an older 911 or a 928 but this one popped up and i grabbed it. Found some interesting things about this car, it was originally sapphire blue metallic so I will be putting it back it also had 4500 dollars worth of service done with records in the the last 12 months and was driven less than 3000 miles since that work.

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[/QUOTE]Also one note... the late cars (which includes 1986) use an AFM that uses a ~5v regulated reference voltage. The early DME used ~12v (unregulated) with an 8v minimum, so the 9v battery trick is really only applicable to the early AFM unless you wire in some other known voltage drop. I would wire some 1.5v batteries in series until you find a combination that gives you somewhere between 4.5v and 5.5v, one battery may need to be somewhat used up.[/QUOTE]

Sausagehacker, this is very interesting as I did test it with a 9volt and the numbers fell as described. I will try it with the lower volts and see what happens. Looks like i have a busy weekend ahead of me!