Danton

Hi,
The other day I took the car for a drive and it ran quite poorly. The idle has dropped to around 400 rpm. When I try any type of acceleration there is a lot of vibration in the steering wheel. I can even see the rear spoiler shaking. But once on the highway at a steady speed you wouldn't know anything is wrong. Oil pressure is good. I'm thinking a loose vacuum hose somewhere but can't find one. I'm not familiar with this engine at all but very much so with the 951. Can someone steer me in the right direction as this has got me down somewhat. I really hope it's something simple...

bd0nalds0n

Are you sure it's running on all 8 cylinders?

Danton

I'll check that today and get back to you. thx!

hupp

Does it vibrate at idle too or just under acceleration?

hinchcliffe

Check plugs, wires, distributor for loose parts. Could be spark plug wires. Chekc those and get back to us.

andy-gts

I had the exact same thing happen after I got the car back from the dealer and I found a leaf next to the maf..sucked everything out and the car ran great...go figure...did the car sense problems the the resistance of the screen of the maf and run on limp mode??
any way something simple..
andy

Imo000

Yup, sounds like she’s not running on all 8. I had this happen once. By mistake I mixed up the IAT sensor connector with the last injector on the driver side. Since you don’t drive the S4 that much I’m guessing that one of the injector is probably stuck closed. While the engine is running, try pulling each plug off one at a time. The one that doesn’t make a difference is the cylinder you should start looking into. OR if you have a laser thermometer, lift the car when the engine id cold. Then start it and measure each exhaust port temp. When compared to the others, the one that’s not firing will be really cold.

I hope this helps!

Danton

It doesn't vibrate at idle, only under acceleration in gear. But the idle is lower then normal. I did try pulling the plug wires to verify if all cylinders are firing but didn't learn much. In my 951 if you pull a plug wire the car idles like total sh*t and that's what I was looking for. But doing the same in this car you barely notice anything. I will try again today and look for even the smallest deviation in the exhaust note. And sorry, no laser thermometer. Thanks for the help guys!

Imo000

I had a failed (stuck) injector on my 928 and it took a long time to find. The disadvantage of a V8 is the fact that there are 8 cylinders. As you noticed, removing one spark plug wire makes very little difference at idle. What caught my attention in you description was that is shakes under acceleration. That’s exactly how mine acted too. At idle it seemed normal but under load the problem was a lot more evident.

Mark

Could it be in 'limp home' mode?

Do you have any 928-knowledgeable friends that are also practical jokers...maybe they connected the limp home connector? (Or - did you happen to be in the fuse panel area, and connect it up my accident?)

Shark Attack

I assume this is your 87? it sounds to me like you are running on 4 cylinders. I had an 89 that did this, the PO had the plug wires on wrong. So i know that engine will run on only 4 cylinders. at itle it sounded fine. Does the 87 have the split egnition system like the 89? if so i would check for spark on all 8 cylinders.... one of your ignition modules, distributors may be toast

Danton

I pulled the plug wires today and it seems each cylinder is firing. At least for the moment. Thing is when I was done I took her for a quick spin and she ran fine. So I must have done something by either pulling the plug wires or removing the air cleaner box. Now I have zero in on what it is. I'll play with it some more tomorrow. Like someone mentioned maybe I have an injector that's palying games! :-)

Danton

Ok... Today I took her out for a quick 10 minute spin and she ran fine. The low idling and heavy vibration were not there. Then before I put her away it came back. I open the hook just to check things. I noticed a slight whirring type sound coming from the engine. I start poking around and find a hose that is very soft to squeeze.. too soft. Now there are two approx 3/4" hoses coming from under the intake and going into the valve cover on the passenger side. The one towards the front of the car came apart with a good tuck which also showed it had a crack in it and was leaking. Can someone tell me what these are for with maybe some part numbers? Also how big of a job is it to replace them. And please forgive me for my lack of 928 knowledge. Any help is appreciated!

I edited and attached a pic showing the hoses. Not my engine BTW..

Shark Attack

ooof. if it is the same one on my 89 the plenum had to come off. and they told me to do everything under there while i had it apart, the total parts cost was $700.00 I think they are just breather hoses but i know mine leaked a lot of oil out of them. good luck. a few pix may help the guys ID what the part is

hacker-pschorr

I had this problem few years ago. Easy to check, pull off each injector connector one by one. When you find one that does not effect how it runs - bingo!