Joe6pack

I did a search, but I wasn’t able to find a similar problem. Since I am new to Porsches and air cooled cars in general, I don’t have a firm grasp on what is “normal”. Here is the problem. When sitting at a light the car will idle what I would call normally at around 800 rpms for awhile. Then, suddenly, the rpms will drop to about 750, the oil pressure will drop and the car will noticeably shudder. It will stay like this for a few seconds and then the rpms may climb a little. It has never died. It will do this with my foot on or off of the brake, A/C on or off, lights on or off, etc. I have looked for vacuum leaks and tightened everything I could find. I pulled the IAC and verified it is working per the Bentley manual. I pulled the oxygen sensor connector and nothing changed. The temperature of the engine is at or below the lower mark (it’s been quite cold here recently). Off idle, the car pulls great.

Any help would be appreciated. I just joined PCA and I plan to attend some events in the Peachstate Region so that I can become better acquainted with my car, but right now this is really bugging me. Thanks in advance for your assistance on this.

John

Steve Weiner-Rennsport Systems

Remove & clean the (brown) ground wires on the intake manifold. This is a common problem,....

Amber Gramps

IAC=ICV or idle control valve???

That is my first guess. Next would be an intake manifold leak.

Joe6pack

Wow, thanks for the quick replys. To answer the questions:

I don't know the age of the O2 sensor. I have only had the car since November. When opening the oil filler at idle, the rpms do drop. This is an '87 3.2 and it recently passed GA emissions. However, I don't have the numbers in front of me. I'll try cleaning the ground wires. A bad ground would make sense. I have seen similar problems on American cars. IAC=Idle Air Control Valve (I think that's what it's called). Thanks again for the quick replys.

John

salukijac

Wow, my car normally runs at 1100 at idle. I'm surprised a drop of 50 RPMs will have that much effect. Please let us know what you find.

Amber Gramps

Make sure your aren't using your cruise control cable as your idle stop. The cable can be too tight and cause this issue. It could also be vacuum leaks.

dshepp806

That intake manifold ground will surely do it...

ICV would be my next check (clean/lube)...

then off to look at O2 sensor measurements and idle settings (measurements).

Best,

Doyle

theiceman

doyle that was your issue too right ?

dshepp806

It was recently, for sure. Found it loose a few days after getting it out of the shop...had a real lopy idle,..shook/vibrated the car...she otherwise ran great........I had removed the ICV,..cleaned it up and lubed her with no magical results (althought the ICV is a better ICV now.....measurements are good and movement was smooth,..AFM was next on the list...a passing visual found it,..not even hand tight. Gave it proper torque and ,..guess what?....the lopy stuff went away. On recollection (only), I think it was G406 ground point(?) Certainly, the intake manifold ('89 Carrera) ground....lotsa' ground points there for several important things (look 'em up...)...

yes,..in my case.

Best,

Doyle

Joe6pack

Good call Steve and thanks everybody. I removed the ground bolt and washer and cleaned up the loop terminals (there were two). When I went to put it back, I discovered that the bolt was actually stripped. I replaced it with a new one and tightened everything down. Unfortunately, I wasn’t able to test it out, but this definitely was a problem. Hopefully, it was THE problem.

Thanks again,

John

theiceman

Well I have been in service for over 25 years or so and when i teach people it i always the same thing " fix what you can see, before you fix what you can't see" . It is amazing how successfull people can be following this advice. I think you are definitelyon the right track regardless.. please report back

Ed Hughes

Well, if a car is idling that close to redline, 50 r's ain't gonna change much.

Why is your car idling so high? That would bug the heck out of me. The 850 neighborhood is where you should be.

salukijac

Ed,
The car has always run around 1100. Yesterday I looked more closely and it was around 1050. Two different mechanics (the first one performed the PPI) have seen the car and I was never told me it was running high. In my mind I thought it was normal.

I guess I should start poking around with the Bentley and see what I can find out. Doug mentioned the cruise control cable.

I guess I better start my own thread.

ron mcatee

+1 for 850 rpm at idle.

Joe6pack

Well, I thought I would give an update on my idle woes. After cleaning the ground, the car does seem to be idling better. However, I am still experiencing the idle drops. They seem to be fewer and farther between, but they are still there. In fact, the severity may have increased. Also, the idle has always felt "lumpier" than I thought it should. In looking at the tach, I would say that I am idling closer to 800 rpms than the recommended 850. With that, I may try adjusting the idle speed as mentioned in the other idle thread that split off of this one. I will also try cleaning the other grounds, etc. I probably put 100 miles on the car this weekend and other than the idle, it ran great.