Ron_H

Engine ran just fine except for two problems:
1. failed smog test at 15 mph (to high NOX = lean)
2. idle problems. let off the throttle at slow speeds or approaching a stop, and it either dies suddenly or starts surging / lumpy idle and then dies. I had to drive using my left foot for braking to keep the rpm high enough to keep the engine running.

I decided to replace the throttle position sensor and the accompanying wiring harness. As well, I planned to replace the intake manifold runner gaskets.
I tore into this with eagerness expecting to also pass the smog test and be a happy camper once again. I was wrong. After getting to the throttle body with
half of the runners off and the other half loose (the bolts for one bank were only hand tight!!), and in conference with Greg Brown, it was suggested that I test the impedance of the throttle position sensor before replacing it. Surely enough both the new and the old tested identical in both full throttle and idle settings, so I took Greg's advice and let the old sensor remain in place but replaced the short wiring harness that connects at the front of the engine. Along the way, I managed to over torque the bolt that holds the bracket for
the idle stabilizer thingie. That bolt also holds down the throttle housing, and it is bonded to the block somehow (epoxy?), which is the first Porsche part in 50 years I would regard is idiotically conceived because I was easily able to break it free from the bond to the block so that the throttle body housing could rock up and down. I epoxied it back into place but did not use JB Weld so I doubt it will hold in place. While in there, I found the electrical connector lying in the valley drenched in oil (see photo). Does anyone have a clue about the purpose of this connector? I also found a stray white plastic vacuum line attached to nothing. I should have plugged it. Last night I buttoned up everything and was careful to put everything back where I think it belonged, including the injectors I had unplugged from the intake runner bases on the passenger side, after first applying a light coat of machine oil to the seals. Happily I put the key in ready for a test drive........which never happened. The engine started, sputtered, coughed, wheezed, and then I gave it some throttle which caused it to instantly rev smoothly up to about 4500 all the while emitting a terrible whistling scream until I let off of the throttle. Massive air leak I suspected and it would not idle without coughing, back firing and running lumpy. No test drive last night, that's for sure. I must have missed something.

I reason that I must not have re-installed the injectors on the passenger side of the engine correctly. Would this cause such symptoms? I think they are not snapped into place and are just spewing fuel into the head while allowing false air to enter as well, and that accounts for the whistling noise. I also suspect the throttle housing which is not anchored on one side and can rock sideways. Could that account for the rough running at idle or light throttle? If it is the throttle housing, the part will need to be removed and the block drilled and inserted to allow use of a threaded bolt to hold it to the block. The third suspicion I have is the intake gasket type. I used the paper gaskets, and they replaced the metal with rubber "o" ring gaskets already installed. I think the metal gaskets are much better.
but it was explained that the metal ones are tremendously more expensive. I think I should have used the metal ones. Could those gaskets be responsible for the leaking air and thus the impossible running conditions?

Any suggestion? I really don't like taking the bus and my Saab died (blown engine).

Chalkboss

I believe that is a diagnostic port that is no longer supported/used. Your injectors should firmly seat into the rail and manifold, and the U wire clips should likewise be securely fastened and the harness seated all the way onto the injector. A loose harness will cause many problems...

WallyP

The connector looks like the never-used dealer diagnostic connector. If so, it should go to what appears to be a second crank position sensor. You don't need it.

I thought that the vacuum line might be between the flappy valve actuator and control solenoid on the left front corner of the engine - but you don't have that. Make sure that it doesn't go to the heater control valve or the recirculate flap actuator under the blower, above the passenger's toes above the grille.

The epoxied fastener sounds like one of the rubber mounts. If so, the mount consists of a small rubber cylinder with a flat plate about 3/8" bonded on each end, and a threaded stud welded on each plate. Replace it.

I like the expensive gaskets.

You can use a 4' rubber or plastic tube as a stethoscope to listen for and localize vacuum leaks by sound.

Make sure that the large O-rings on the throttle body and MAF are good and pushed in properly.

There are several rubber elbows and connectors that are prone to splitting as you put things back together, especially on the throttle body.

Good luck! Ask questions as you go, not after you finish...

Ron_H

Thanks for the responses.

I had torqued the throttle body support nut/stud too hard and broke the nut with part of the stud off so the remaining stud could no longer accept a replacement nut. I found another stud and epoxied it to the engine case. Time will tell if it will hold.

The injectors pulled free from the intake runners with I removed them and then the runners to access the side of the throttle body holding the throttle position sensor. I didn't notice any u clips and that may have been the problem: they are not seated in the runners all the way.

I did notice several u shaped vacuum tubes to the throttle body and thought I was careful not to damage any as I tightened the hose clamp around the central intake tube body to the throttle body. One of the hose clamps sits just next to that vacuum tube elbow.

I can't listen to potential air leaks because it is almost impossible to get the car to idle long enough to do so. Only full or almost full throttle will keep it running, and lessening the throttle will cause it to drop down to what sounds like only 4 cylinders running erratically, and then it shuts off. For that reason, I suspect one bank of cylinders is the source of the air leak, more specifically the injectors not being seated properly. I'll need to educate myself on proper removal and installation of those injectors. The fuel rail is seated properly and secured so I just assumed I had pushed the injectors deeply enough into the intake runner ports. The air leak scream reminds me of a supercharger sound on an American V8 when it starts to rev. Piercing. Scary. I shut it off and walked away before something happened that would be ugly.

Wisconsin Joe

Cigar "smoke test"?

Get a stogie, light it and blow some smoke into a vacuum line.
It will take more than a couple of puffs to fill the intake, but you should see smoke coming out of where ever it is leaking.

Chalkboss

To get an idea of how the injectors mount to the rail and harness have a look at Dwayne's most excellent write up.
http://dwaynesgarage.norcal928.org/1...%20Refresh.htm

Good move on backing away and going off to think about it!

chitown928s4

Well I just went thru the piercing sound. Turn out one of the intake bolts wasny tightened 100%. You can try and isolate by spraying starter fluid in the area of the sound then at the bolts. If the sound changes you found it.

j.kenzie@sbcglobal.net

Propane torch can also help localize vacuum leak, with less chance of fire.
Dave

WyattsRide

I was experiencing what sounds to me like similar symptoms you are having, with my 85.

Did you check that all vacuum lines are properly routed and the elbows and 7 way connector are not cracked and leaking. Are you sure that your "T" over the throttle body is seated properly and both screw clamps are tight? Did you check your Idle Stabilizer Valve? Is your MAF new? This is a long shot, but for any reason did you mess with the Ignition Modules ( or Ignition Amps) at the front left of the engine bay?

Ducman82

idle air control hooked back up?

Ron_H

Thanks again to all who have replied. I have been busy studying Dwayne's excellent and well photographed post and have made a list of items to re-check, as well as embarrassing errors I found in my process. This weekend I will likely retrace all steps to correct them.

Yes, the ISV is new and connected properly; actually, it was newly installed a few weeks before I began this latest expedition into improving the idle and low speed behavior of the engine which had otherwise been running quite well (just not California smog compliant at 15 mph!). Now it seems it won't run well at all. The vacuum elbows were mostly tightly fitting, but a couple were not and should be replaced. One was disconnected and I still haven't found to what it was meant to be connected. I might just plug it temporarily while I search for a cure. It is around the water filler bottle near the firewall on the passenger side. Actually, I am assuming the ISV is good because it was purchased new though that doesn't insure parts are operating properly. I wonder if it can be tested. It was my first stab at curing the erratic idle and it made a slight bit of difference but not much.
My intake bolts were tightened to what I thought was a uniform and acceptable amount, but I used that paper gasket, and before finishing this project I noticed that some oil had gotten onto it before the final placement of the intake runners. Perhaps it isn't compressing equally in all places. I really think that is a 1950's solution; I recall making those out of gasket material and ball bearings to cut the bolt holes because we were in high school and had little money. The metal ones seem superior. I still have no money because I didn't listen to my father and marry a wealthy girl.
Another item I suspect are the injector seals. I had planned to order some from Roger, but I had a deadline for completing this job (bad news strategy with any car, but particularly with P cars) and went ahead without completing the order. Now I will order them, because I may have damaged an old one removing and re-installing them. All of these "oversights" must be checked now. As well, though I quit smoking many years ago, I'll try the cigar smoke method suggested if I can get the car to idle long enough to apply it. Currently, it will not idle more than a few seconds before dying.
Yes the T section was carefully tightened as it fit over the throttle body, I thought. However, I did spray with WD-40 both that circular rubber sealing ring and those around the runners to the plenums before assembly because it helps slide them on and off. I wonder if I applied too much or didn't wipe off the excess sufficiently. At least I will remove that T section and the runner seals and wipe both surfaces. The T section is always a problem to get sufficiently tight without using a socket instead of a screwdriver; I will get it tighter.
The MAF was borrowed from Bill Ball who declared it in good condition; I tend to trust Bill's opinion. My original MAF is still sitting here after being removed from the car in hopes that it was the cause of the high NOX readings and smog failure. Unfortunately, it wasn't because the readings remained too high and no improvement was noticed using Bill's MAF over mine.
Now it is back to Dwayne's excellent article for more discovery.

I just finished Dwayne's post and thanks to Don for recommending it. Although some of it applied specifically to S-4s, much of it was applicable to both S-4s as well as my S-3. It gave me many areas to check and I'll tear into this issue again next weekend.

Wisconsin Joe

No.

Car off. Blow smoke into a vacuum line and see where it comes out.

If the car is running, it will just pull the smoke through the engine.

WyattsRide

You can bench test the ISV with 12v battery. Neg to the center male plug. Positive to either end male plugs. One side opens and the other closes.



This shows new vacuum line routing and existing.
http://s287999742.e-shop.info/online...IAGRAMS+S3.pdf


Remove all the lubricant you used for the rubber connectors. These should be dry and grease free when connecting. This is from a very respected 928 mechanic here. They'll go on without lubricant. Believe me. I've done it many times recently.

MikeinBloomfield

My car is an 82, so an altogether different animal, but this is what my car did when it had a massive air leak at one of the injectors. Wouldn't hold idle unless I turned the idle screw all the way up (an option you don't have) and otherwise ran as if it had a miss. Didn't have a whistle, but I did have a sound like rushing air.

Shop finally fixed it after I took the injectors out and and put them in again three times (as well as changing the AFM, testing the vacuum hoses, etc.). I still don't know what I did, but I just could not get the injectors to seat well. I could screw in the brass tie-downs, but it's obvious one of the injectors weren't sealing.

Ron_H

Yes Joe. Car should be off. I was thinking I could see the smoke being sucked in by a leaky connection or bearing seal. You method makes more sense.

Thanks for the links Rick. I will remove all the lubricants I applied in haste. It was getting dark and I was losing patience and should have just quit for the day. I can clean that all up in a jiffy, including the sleeve between the throttle body and the T duct. That's really the one that concerns me. This weekend I'll get to that chore, plus change all the injector seals and U clips, plus a whole list of "do-overs" gleaned from Dwayne's article.