My 84 Targa is experiencing the following. Once in traffic while at a stop light it began a pulsing idle and stalled. I restarted just fine and the problem was gone. The other day I started the car and it began a erratic loping idle bouncing wildly between 500 and 3000 rpm. Touching the throttle only aggrevated the problem. The car sat for 15 to 20 minutes and the low rpm moved up to about 800 but was still erratic but not as bad. Again touching the throttle made the car rev up and down on its own. The car was of course non-drivable. I shut down the engine and restarted. The probem magically disappeared and the car was fine all the way home. I am thinking faulty sensor or computer problem. If it happens again and I can find them I want to unplug sensor input one at a time to find the faulty one. I bought the car two weeks ago. It has 77,000 miles and the 75k maintenance was supposidly done but, I can not prove it.

What do you guys think?

I also want to refurbish all Targa roof and car top seals. Ideas for sources of material? Lastly the antenna motor (and cigarette lighter) are out of commision. I have not yet checked fuses. What's a motor run? Sources?

I'd appreciate any and all help as the car is parked until I can figure out the idling problem. As the next time it might not go away and I'll be stuck.

Thanks.

reg



FYI got in touch with a (the) local Porsche dealership service manager. He feels its could be the O2 sensor but is more likely the idle control valve. Repair costs: $400.00 (shop). I'll back this up with the maintenance manual once it arrives. If not too expensive I am going to change out the O2 sensor first.

Guys,

So far I have gathered the following causes. I listed the part prices low being mail order high is dealer (Richmond, Va).

Causes:

1. Mispositioned set screw on the FI system. If set too high all air is bypassing control valve. Adjust as needed to lower idle if too high. Clockwise to lower RPM. Free if you do it. Thanks to Bob Novus for this one.

2. Head Temperature Sensor. Bad sensor can cause erratic idle and stalling. $50 to $75.
For my 84 Targa if I replace this it will be with the upgraded, twin grounded version. My service manager suspects this over the O2 sensor.

3. Oxygen Sensor. Most expensive fix if replacing. >$200.00 to 225.00 I can see why people just unplug this. Besides I think you need a special socket.

4. Idle Control Valve. ~$150

5. Throttle switch. ~$70.00

I plan to troubleshoot in the above order.

Hope the information is helpful. Will keep all informed of my results.

Reg

 

I have a similar problem with my '85. On cold starting, the motor revs wildly between 500-1500 rpm for about 10 seconds (longer in cold weather.) I replaced the O2 sensor which seemed to minimize, but not eliminate the problem. I have asked numerous authorities about this, from Bruce Anderson, to the local Mercedes shop, and they conclude, "oh, they do that." The car starts & runs fine otherwise & passes inspection, so if you can get rid of the warm running problem, you should be ok. Hope that helps!
Tom

 

I've got the same problem with my 85 930. I've had it in the shop twice. My mechanic is great but we can't seem to figure out what the problem is. First, he replaced the spark plug wires, which were apparently arcing. This did not fix it. Second, he cleaned the coil, which was corroded. This actually seemed to fix it for a while. Now, it is doing it again. Mine seems to jump from idle to about 1800-2000 and back down again. Any ideas are appreciated.

 

Sorry JD I left a reply here and then decided to move it to after my message at the top. Somehow it stamped my name on your 85 930 message. Sorry again. I'll see if the administrators can fix it.

 

It's both a warm and cold problem. What I can't figure out is how restarting the engine fixes the swinging.

 

R,

I have the same car and a few years ago had a similar problem. After several tuneups and the same problem, I changed the mass airflow sensor and the problem went away. I'm no expert but the problem never came back.

Tim

 

mine was doing something somewhat similar. i replaced the fuel filter, plugs, wires, cap/rotor, used 2 bottles of fuel injector cleaner and still nothing. turned out to be a vacuum leak b/c a hose started to crack. once that was replaced, it was like a new car. where mine cracked was right behind the heater blower on the left - where the copper pipe has a rubber fitting on the end. if the rubber is indeed cracked a good mechanic can do a homemade fix for $10 instead of the $300+ porsche part.

before you change your idle control valve, take it off (simple), and clean it out w/ carb. cleaner. that helped my problem a little bit. the manual can also tell you how to see if its working or not.

as for targa seals - DON'T TOUCH THEM. check out the archive board for what others have said to get a general consensus, but i've heard that its best to leave them alone, and check some of the other stuff, like the latches for example. they don't make the same seals anymore, no matter what anyone says. the ones they sell fit, but they're NOT the original ones. not sure where you're located but in nj there's a porsche salesman (dan) who has a targa biz on the side (carsinc1@aol.com) where he refurbishes/fixes targas. he's legit, and while i've never used him personally, i have met him a few times and he knows porsches in and out.

good luck!

 

try lowering the idle speed a bit. also see if the microswitch on the left side of the throttle housing is being activated when the throttle is closed. you can hear it click just as the throttle is opened. (engine off)