R44flyer

Good day everyone.
I am a new owner of a 88 928S4 5 speed. It has a lot of issues, but it is my long term goal to restore her. I have had her a few days and after she warms up (it's in the 40's here), the idle drops down then up..... TBH, I am not a trained mechanic, only a hobbyist. I know that vacuum leaks could be the cause, but I am not sure where to start looking. Any guidance would be appreciated.
Thanks,
Karl

Speedtoys

Smoke test..start there...there is no one place to really start looking, than know where they are by testing them all.

Highly likely that a top end refresh is the top of your list...even if I said "Oh, probly the idle stepper motor..." that will disturb so much ancient rubber and plastic, you'll be doing a top end refresh anyways.

R44flyer

Thanks, just ordered my smoker :-) Never used one before. Looks like fun. Anything I should be cognizant of with the 928?

Speedtoys

Keep a stack of money handy..lots of small pieces/hoses/etc in a top end job. Including fuel regulator, two pressure dampers, and the idle motor..those 4 will be eye watering by themelves, but cant be skipped, and fuel lines.

The front Xover hose is still available, and not too bad, but the rear and front high pressure lines must must be replaced.

Engine bay photo handy?

R44flyer

R44flyer

This is what was reported as to have been done right before I bought it:
Spark plugs
Dryer and expansion valve
AC compressor 134A
Intake refresh of all gaskets
Valve cover gaskets
Oil pan mod.
Throttle body linkage cable
Rear latch
All motor sensors
Shift linkage bushings : front and back
Window regulators
Window motors
Rebuilt MAF sensor
O2 sensor
Fuel lines
Fuel sensor
Fuel tank
Fuel filter
Cam sensor
Crank sensor
Knock sensor
Flap valve
Solenoid
Brake lines
Bosch fuel injectors

mkhargrove

go ahead and buy a 20 lb box of 10mm sockets

Kevin in Atlanta

Based on the pictures above I'm a bit skeptical that much of that list was replaced recently. Did you get any records that back that up?

copperstew

Your idle issues could be from your electrical ignition (check the WSM for the troubleshooting proc.). Rule out the ignition system before you start in on the fuel system.

Clean the ground points. In your photos those are the bundles of brown wires bolted to the body. They don't look like anybody has cleaned those ever. There is a list of them in your manual. They need to be unbolted, cleaned with sand paper and reassembled. You can coat them with copper grease, dielectric grease or cosmoline to slow oxidation.

You should take the CE panel out of the car and clean it on your bench with a dremel until all the copper is shiny. I did this last summer and it took me 5 hours total for R&R and cleaning. If you clean the grounds in the engine bay and at the central electric panel you can at least eliminate those as a cause. You'll have to do it eventually anyway.

You should also replace the two ground straps on the engine and the battery. Those two are easy to replace and not too expensive.

Since your grounds are neglected, I question if the previous owner actually did all the work he claimed, or if it was done it probably wasn't done recently. Maybe 5 years ago looking judging by those spark plug wires (I have no idea how dusty Texas is).

Your brake booster looks so rusted it will probably need to be replaced as will the master cylinder. You don't want rust from those components getting into the "new" brake lines.

R44flyer

Thank you both. I appreciate the helpful comments.
The young man I bought the car from is a "garage mechanic" who has apparently done work on/sold other 928's in the past. While I don't want to say specific negative things here, I am getting the distinct impression that a lot of pertinent information may have been omitted from our conversations.
It is going to be a long road I imagine.....
Regards,
Karl

copperstew

I don't mean to discourage you. The electrical diagnostics on this car are fairly straightforward. You can do a lot using a light probe and a good multimeter.

It will be cheaper to sort this car electrically first and then investigate the fuel system after. Those fuel parts are sometimes not available new from Porsche and when they are they are hundreds of dollars each for the little vacuum regulators and dampers.

Once sorted, these cars are just brilliant vehicles.

R44flyer

LOL, the omitted information I mean was between me and the seller :-) I am not discouraged. It's just got a long list of things to do...... Thanks CopperStew!

Mrmerlin

You need to do an INtake refresh

R44flyer

Thanks Mrmerlin,
As a newbie I am not sure what that entails and a quick search I did here was a little vague. Can you give me a little more info please?

Zirconocene

Look up Dwayne's Garage. There are a ton of great procedures documented that you will, likely, undertake.

I haven't totally studied all the pictures you uploaded but there is at least ONE fuel line that is new; looks to be one of Roger's (from 928sRUs, you'll become acquainted, along with some of the other great vendors).

Cheers