Shuddering

Okay. So my 1988 928 S4 was back on the road and running beautifully. However, while giving the car up to about 1/3 throttle, it shudders like nothing else. I don't know if the issue lies in under inflated tires, bad coils or a timing issue, but it's driving me a little crazy every time I take off from a red light. It goes away if I put the pedal down, but it shakes the whole car if I touch the gas even a tiny bit up to about 1/3 like I said before! Hopefully someone will have some experience with this or a helpful hint they can send my way. Thanks again!

This is an interesting problem. There are so many possible causes, you need to set up a diagnostic path and follow it.

a) Is the engine in tune? When were the spark plugs, rotors, rotor caps changed? Have the spark plug wires ever been changed? The 1985 and newer Porsche 928s have two spark systems, if 1/2 of the engine cuts out it could cause a shudder and certainly loss of power. From model year 1989 there are sensors that will shut off to fuel to the 1/2 of the engine if spark fails.

b) There are fuel related issues, a failing LH fuel injection module or mass airflow module could cause these problems. Fuel pressure regulator and pressure dampeners will fail with age. You need to check the fuel pressure.

c) There are mechanical issues, possible thrust bearing issues that cause the engine to "bind"

Drop me a note at info@electronikrepair.com and I can provide more detailed information.

Rich
928 Owners Club Charter Member & Membership Chairman
1993 928 GTS Cover Girl
1987 928 S4
1979 928 5-speed - now in print
1979 928 track beast

Hey there thanks for the quick response. I have checked into these issues and I will continue to follow the diagnostic path. I am looking at the symptoms of a failing or failed TPS and they all seem to check out with what I have been experiencing. I'm going to talk to a mechanic today and see what they say. Thanks for the input!

The very first thing to do is to rule out mechanical reasons for the symptoms. DEFINITELY check your crankshaft preload. There are several good writeups online explaining how to do this. You'll need a micrometer if you don't have one already. This should be done annually as this check will also relieve the flex plate.

Once you rule out the less likely, though catastrophic, thrust bearing failure, inspect all of your ignition equipment and verify that your holding a good and steady vacuum.

With '85 and newer cars, the MAF is always suspect when driveability issues are present. After checking the obvious things first, send the MAF to Rich Andrade for an assessment/rebuild.