Hessitation solved on a '82 SC (long write-up)

[wesayso]

After a few weeks of agony I have solved a hesitation problem on my daily driven '82 SC. I am typing this (long) story to maybe help others who encounter this problem. (who use the search function in the near future).

It all started with a change in behaviour of my daily driver about a month after I got it. When I first got the car everything was running well, no hesitation between 1500 - 2500 RPM and a smooth idle. After about a month the idle RPM went up. First when it was started cold and a few days later the idle would be at about 1500 RPM even when warm and if I waited long enough it eventually would drop to 1000 RPM. That's when my hesitation problem started. It would stumble from idle and it felt like I would need driving lessons because I was in the wrong gear all of the time
I had little to no hesitation during the warm up period but when warm my problem would start. I had allready decided my car needed some regular maintanance so I made an appointment with a well known shop nearby.
I had them change plugs, adjust timing and setting CO level, as well as all filters and even the Carrera Chain Tensioners. I wanted to change my Ignition wires as well but once I heard the price of those wires and the fact that my wrench said they seldom go wrong I decided to let those wait. He even checked the resistance and they were ok.
To make this story shorter: after the maintenance the car idled normal again (it was running lean before) and all seemed to be back to normal. That was until the engine was warm again! My hesitation was still there. After reading a lot of good threads on this board I thought I had a vacuum leak somewhere. I started to examine all the usual (to you guys) suspects and found some backed-out bolts in my air filter box. I almost went right ahead to order a new one until I read some more threads on the CIS subjects. I read some guys replaced the bolts at the seam of the air box with a slightly longer bolt with a nut on the back.
Talk about a challange. Armed with a mirror and a flashlight I replaced all of the bolts I could reach. It took me 3 hours to get the back one in the air filter box on the passenger site. Fishing with a wire and looking in the mirror to see what I was doing.... After a long frustrating time I tried to get my arm in there behind the intake runners and up the bottom of the airbox. I grinded one of the longer bolts with a pointy tip and I could just feel it with my finger. I ended up taping a nut to my finger and hooking it up that way to the bolt. If I would have had my garage ready (I'm in the middle of building a new one) I would have taken of the entire CIS system to check and fix everything at once. Well I was succesfull in replacing all suspect bolts and then some (I didn't do the ones on the back side around the trottle body). Next was the test drive! I hopefully went troug the warm up period hoping my problem would at least be a bit better than before. No such luck... Still the same problem in the 1500-2000 RPM range. So my next move was a field adjust using Souk's great thread on the subject:
CIS Idle Speed and Mixture Setting Without an Analyzer

Although this helped to stabilize my Idle (in start stop traffic it would hunt and even drop well below 700 RPM) it didn't help my hesitation. Even more checks on vacuum leaks didn't help any (no leaks that I could find).

From this great thread on the CIS subject I got a better understanding of the warm up sequence:
SC Lambda questions

Since I didn't have an O2 sensor (did it have one originally? It's a '82 ROW SC) I couldn't disconnect it. But I thought I could make the sensor on the distribution fake the engine was still cold. I shorted the temp sensor on the distribution and went for yet another test drive (one of many during this whole searching period). Still no change!
Since I effectively faked a cold engine but still experienced all of the same problems my mind went back to the ignition. In all my period of wrenching on cars trouble with cold cars usually ment the fuel system and trouble when warm would be ignition.
My next test drive was in the dark, to the most dark spot I could find. I opened my engine lid and looked inside: what a mess with little blue sparks around the distributor! The very next day I bought some ty-rips to get those wires further away from each other and a spray can of the stuff to seal ignition wires from water. I immediatly ordered some new ignition wires too! That day the car seemed to drive better but on my way back it had the same old trouble, but not as often as before.
Today I placed my new wires and while I was in there a new muffler because it needed one. What a difference that made! I also got a new rotor (the cap was replaced little before I bought te car) and the new rotor ment I could finally rev over 5800 RPM (the old and tired one backed out to soon and gave me quite a scare the first time that happened ). My hesitation was completely gone and the car felt and sounded new again. This afternoon I relived those happy drives that started my 911 ownership...

So: moral of this story: Check ignition before blaming CIS

Although I do believe my attempts at sealing my air filter box didn't do me any wrong to get this engine run smoother. When the money in my wallet grows back I will be thinking about replacing that part as well

Here she is by the way Black/Red leather '82 SC ROW


If this story helps anybody in the future it was well worth typing it..

Wesayso

(I do hope this is somewhat readable, I'm from the Netherlands so Englisch is not my native language)

[Paulporsche]

Congrats and thanks for sharing your experiences.

BTW your english is actually quite good. If you want to help the board, edit your thread title so that you are spelling hesitation correctly (ie 1 "s"). This will help w/ any further searches.

Also, we often refer to "Euro ride height". What ride heights does your car have? What size wheels and tires?

[wesayso]

Thanks for the kind words, I couldn't edit the title but did edit the post.
My ride height is 24 1/2" at the back and 24" at the front. Isn't that an inch below Euro height? The front sits lower and it should be the other way around but it doesn't seem out of place to me. I guess that's because of the bigger tires out back and the standard tires in the front. The wheels are 8Jx16 with 245/45 and 7Jx16 with 205/45 but the PO cut off the fender lip. If it were up to me I'd prefer to roll the fender lip.

It is low and I have a hard time just backing out my own driveway