Quote:
Originally Posted by Eturbo924
Is the crank end play the same issue as releasing the tension on the flex plate? I was planning to do this over the weekend.
So... any thoughts on the surging? 
You think that is the crank play... or just some thing all 928 owners need to address? |
The heat from the exhaust is worrying - especially if the car is running rough. On later cars (89 or 90 onwards) there's a relay with LED's in it that lights up when the car detects low exhaust gas temps, and which causes the injectors on that side to not fire.
On 87/88's, there are no exhaust gas temp sensors, and thus there's no way for the car to know when its not sparking on either side. The result is it pumps air and fuel into the manifold, which results in an exhaust fire.
The single most likely cause for it to happen is a loose coil lead from the coil to the distributor cap. Check them both, as well as the plug leads, and make sure the ground leads for the coils are attached to their bracket.
Sort that out first - if the cars running on only 4 cylinders its very rough and idle will be lower (had it happen to me briefly last week at the AC tech's - he knocked the coil lead when undoing the high-side pressure valve after charging).
If its only 1 or 2 cylinders that aren't firing you'll get some fuel passing through and it'll run rough, and probably burn - in which case check all the plug leads, in the dark to check for fireflys.
If the surging isn't related to not firing, then it could be a number of things - most likely is a vacuum leak somewhere like the rubber boot that holds the MAF to the throttle, or one of the many vac lines and breather hoses around the intake.
Also worth checking:
Temp II sensor - its the sensor on the right-side of the car on top of the coolant bridge just in front of the manifold (note: porsche convention for Left/Right is as seen from the driver's seat - so right side is the US passenger side). If the sensor shows open circuit on either terminal when put to ground it needs replacing.
Idle Stabliser valve - this is underneath the intake, but you can try cleaning it with WD40 by spraying into the appropriate line just by the throttle assembly. If its sticking idle will surge.
Throttle Position Sensor - there's a test routine for the sensor in the workshop manual that indicates resistance at various positions. Like the ISV its a pain to reach, but you can measure signal at the LH plug in the passenger footwell without taking the intake apart. Most TPS's I've seen on S4's have failed on the high side, but the idle switch still works, but it could be the culprit. (the WOT side is repairable without buying a new sensor)
First order is to sort out the plug leads and make sure you're firing on all cylinders - dumping raw fuel into the exhaust is a short trip to a fire!
Checking the crank end play and releasing the flex plate is just routine on auto 928's - if your car has Thrust Bearing Failure it would normally have shown sooner in the drive than 500 miles, unless its a horrible coincidence.