1985 Carrera rough idle or miss

[Unclduey]

Newbie here, although I have had my 85 Carrera cab for 11 years and SC previous to that for 3 years. The question is my Carrera has 51,000 miles and has not been driven much recently and it developed a "stumble" or I guess a miss?? It seems to miss when I rev it but it goes away around 2500 RPMs or so. The idle is worse after I drive it. So its just the initial starting out where it affects it and I can feel the rough acceleration, it also lacks some power. I put in a full tank of premium and a can of Amsoil treatment and it seemed to take care of the issue until the following weekend - ( sunny day!) it was still there and had to park it. Does it sound like a fuel issue or ignition? fouled sparkplug maybe?

Thanks in advance for any input.

[wolf76]

Hello and welcome. I am trying to track down a similar problem on my '84. I have a stumbling around 2-3000 RPM and as long as I keep my foot down it goes away. So far I have checked for vacuum leaks, replaced the fuel filter, ran some techron, changed the cap and rotor and cleaned the AFM. I am changing the plugs and wires this week as well. I have purchased a cylinder head temp sensor and a throttle switch that will be installed as well. There's a number of good posts regarding this subject here. Try searching for "AFM" or "Cleaning the AFM". Please keep me posted as to what you find.

Thanks and good luck,

Chris

[stlrj]

Originally Posted by Unclduey

Does it sound like a fuel issue or ignition? fouled sparkplug maybe?

Fouled plugs due to faulty ignition cables would be most likely.

The OEM ignition cables are made of stranded copper that short out very easily, causing the associated spark plug to foul out or fail and never recover. For that reason, I would stay away from the OEM wires in favor of the less problematic carbon core variety.


Cheers,

Joe
74 911 w/ 86 3.2 on carbon core Chrsyler ignition cables.

Here it is using HEI rated ( larger diameter ) cap and rotor from a Ford Taurus 3.8.




Extreme wet performance test and with plugs gapped at 0.060":



Try that with stock Beru components...

[kidrock]

Unclduey,

Hello and welcome. Nice looking cab you have there, thanks for posting a pic.

Wolf76 and stlrj are correct. Unfortunately, the symptom you describe could be either vacuum or ignition; you will need to isolate the problem.

The first (and easiest) thing to do (IMHO) is to check for vacuum leaks. Get a can of starter fluid and, while your motor is running, carefully spray around your intake runners, idle control valve and other hoses where suction exists. If you notice a discernable difference in your idle, then you will need to tend to that particular area.

If this test fails to uncover anything, I would move on to your basic tune-up...plugs, wires, cap and rotor. When was the last time these items were changed?

And...do you carry a good DME relay with you as a spare? Very important.

Keep us in the loop, there are many here with more expertise than me. And they're all happy to help get another Porschephile back on the road.

[rusnak]

the AFM is the air flow meter. Try cleaning the ICV or Idle Control Valve.

Probably the best advice is to first charge your battery fully, clean the battery cable clamps, and clean the DME grounds. These are the brown wires that provide ground to the DME system. Clean these electonic connections with a small brass brush, not a rag.

Then you can move on to cleaning and testing the ICV with a multimeter, test fuel pressure, and test the O2 sensor. Also make sure to drive your car. Get it hot and be sure to put fresh premium gas in the car.

[kodioneill]

I wouldn't use starter fluid to check for vacuum leaks. I would use a length of vacuum hose put to your ear to check for vacuum leaks. Most Carrera motronics have a hesitation just at throttle transition. If there is any issue with tuning such as vacuum leaks etc... they will exaggerate the hesitation. Start with the basics. When was the fuel and air filter last replaced ? Old plug wires are a problem also. Pull your plugs and see what they tell, to rich , to lean. Post some photos of your plugs they can tell a lot. I agree that the AFM could be cleaned and adjusted ( many threads on this). Take a fuel sample see how it looks.

[ben parrish]

I had intake leaks but couldn't find them with the "listen with a tube" method. I found the leaks with brake cleaner. When I sprayed it around the intake bases, the idle didn't change so much as the exhaust instantly went white with a distinctive smell.

[rusnak]

Both the tube method and the starting fluid method have been proven to work. Also visually checking vacuum hoses with a mirror and good flashlight works too. It's a good idea to use some of that 1/4" or so refrigerator hose. It is useful for bleeding brakes, and fits in your ear if you are using it to check for vacuum leaks.

I don't know about Amsoil fuel treatment, but I do like Techron and some stuff called 44K by the folks at BG.

[kodioneill]

Spraying flamable arosol on a engine is nuttttttts!

[Unclduey]

Thanks for all the welcomes and responses. Another pic for ya, up for sale shortly!

My records show plugs at 29,000 miles. I purchased with 43,000 miles in 1999 so only 8,000 miles since.....must drive car,must drive car.

Regarding the DME relay, ran into that issue last year, but I do not carry a spare...I will pick one up though,thanks for the reminder.

Picked up some plugs but the damn things sure are deep in the valve cover! I am worried the socket or extension will fall in there, I need to find something bettert han what I have to remove the plugs. Any tricks or a particular tool? I will get some plug wires, cap and rotor ordered as well and report back.

[Unclduey]

Well I didnt get to any of the suggestions as the next time I had it out all was fine. It has continued to run great so maybe a plugged fuel injector??

Anyways all is fine except something new popped up. Under acceleration to shift my seatlbelt light comes on for a few seconds and also the stereo sound goes off for 15 seconds or so. BUT the stereo lights are still on.

Does this sound like a slipping alternator belt or alternator itself? I had posted to MrBeaslys post that my car has the whistle/ringing sound as his in the area of the fan. I am in the Seattle area so if anyone has suggestions on who maybe able to rebuild or repair the alternator if that is the problem.

[Unclduey]

okay, just got in from the garage and looking at the belt. I can turn the fan with a slight pull on the blades, a little pressure is all . Is the belt too loose then? So from what I am reading I need to relocate a shim from under the nut to the outside, total of 6 shims? I know I will need to get a new belt but until then.