1988 Porsche 928 S4

For your consideration is a 1988 Porsche 928 S4 which was reportedly 1/5 optioned in Diamond Blue Metallic (special color group for 930 Turbos) for the US market. Original sticker in 1988 was $70,000, which would be about $190,000 today, making it the 3rd most expensive production car in the world at the time. 
I drove the car cross country from Virginia to Texas August 2024 with a 10 day, 4 wheels up and off, pit stop to prep it for the distance. Pre-journey prep included fluid change/washout  (rear differential, engine oil, coolant), spark plugs, A/C recharge, crank shaft endplay check, and numerous inspections. Gas mileage on the highway was 18-21mpg from St. Louis to San Antonio.

Since then it has spent much of its time in storage as I have been focused on partial restoration of another Porsche 928 which is now my daily driver. I’m taking a new job in Summer 2026 and won’t have time for both 928’s. This one is a mechanically sound and excellent candidate for a slow restoration while enjoying it between projects. This would be a great parent-child project. For those unfamiliar with these vintage super cars, the community that has preserved them has compiled the most comprehensive library of procedural, instructional and diagnostics materials I’ve ever seen for anything.

It’s my opinion that the 1988 928 S4 is the 928 to have. 1988 was the last year for analog electronics, and nearly every component is serviceable or rebuild able. Replacement parts are relatively cheap compared to later model S4/GT/GTS with digital equipment. Rated at 320hp and 317ft/lbs of torque with 4 piston Brembo front calipers and major suspension updates, it set a new bar for 928 performance. When these cars are running as designed, they are effortless grand touring cars.

Sean Ratts (928 Docs) inspected and drove the car in AUG2024 en route back to San Antonio and commented that it had “a very strong motor” and a few of the usual annoying things that require an interested owner to remediate. Since then, the following have been done: - services and repairs will be updated on Carfax ahead of sale so records can be rebuilt for this car. No service records beyond what’s on Carfax. I solid survey has been conducted on the vehicle and is outlined below. The car has a long life ahead of it with regular driving and proper maintenance. If you want a 928 that’s not going to cost $4-5K a year to keep driving, this one’s for you.


Services/preventatives/diagnostics under current ownership: 
- the majority of these services were recorded in 4K with a GoPro. I will also include raw unedited 928 procedural video (~800GB) which covers general maintenance, some electronics diagnostics/repair, proper stereo install, timing belt/water pump, timing check, interior removal and reassembly, pod/dash removal and reinstall, and more (which will be for private use only).

1- crank shaft endplay and flex plate release AUG2024: .152mm (average of 6 measurements- 3 pairs with 2 different gauges)
2- Crank shaft endplay and flex plate release SEPT2025: .154 ( average of 3, single gauge). ~1.5mm of movement.
*** factory spec .11-.33 with wear limit .40 so there is are miles and miles to go before a bottom end rebuild. Crank shaft endplay is still nominal after 37 years.
3- complete coolant system flush with DI water, refilled and pressure tested. AUG2024
4- new coolant reservoir cap
5- new proper AGM battery 
6- block drilled/tapped for A/C tensioner bracket which was stripped during service in NC by prior owner. (Next standard size up, so no need to worry about keeping track of an oddball wrench in your kit)
7- All fuses replaced with proper rating 
8- multiple relays replaced
9- CE panel (fuse/relay box) cleaned, deoxidized, and treated with Stabillant 22 (pre/post systems checks recorded)
10- main engine ground cleaned 
11- Airbox mounting hardware replaced including rubber bumpers 
12- driveshaft pinch bolts replaced (which means they need to be retorqued in approximately 1000 miles). Edit- Driveshaft splines loctite’d, zero movement at +1000 miles
13- fuel pump and fuel filter replaced. SEP2025
14- HVAC actuators vacuum tested. One leaking, new part included in sale
15- Cruise Control and vacuum reservoir tested and working
16- A/C system recharged AUG2024. New receiver/drier included with sale as well as spare used compressor with working clutch.
17- high beam wiring repaired, bulbs replaced and working 
18- numerous other minor services, fixes and function tests conducted 
19- transmission pan gasket and filter replaced and gravity wash ATF washout from Trans cooler return hose to rear.
20- aluminum radiator installed
21- sunroof and windows all work, new switches installed
22- Porken tensioner has ~1cm of throw left. 
23- Hatch struts replaced 14JAN2026
24- oil change AUG2024 20W50
25- oil change MAR 2025 20w50
26- oil change SEP 2025 20w50 with Ceratec Additive
27- Power steering reservoir, filter and low pressure hoses replaced SEP2025
28- speed mount installed SEP2025
29- transmission adjusted by Sean Ratts in Argyle, TX 
30- Modified for push to start (switch rated for 3,000,000 cycles)
31- 3M Nano Ceramic tint, Texas legal limit.
32- Head Gasket chem test - zero color change APR2025. I’m happy to conduct an updated HG chem test on a video call or in person for serious buyers.


Under prior ownership:
- rebuilt steering rack
- Driveshaft upgraded to 25mm
- Transaxle looks to have been replaced/rebuilt and the torque tube bearings appear to have been replaced. I cannot confirm but considering the driveshaft upgrade and the general condition/function it’s very likely. 
- Brake master cylinder replaced
- Porken Tensioner, Timing Belt and Water pump done circa 2020. ~16K miles on Gates belt. Recommendations vary a lot but Gates says 50K miles or 8 years. WS Manual is 60K/5 years. With the amount of room left for the tensioner, I would be personally be comfortable with changing it early 2027 along with the water pump.
- Rebuilt ECU/LH
- upgraded fuel injectors (4-hole)
- interior headliner
- aftermarket touch screen double DIN head unit. Backup camera needs to be properly wired and setup but is installed 
- rear interior quarters replaced 
- Rockford Speakers in the hatch 
- oil pan gasket
- motor mounts (speed mount was installed for some extra cushion)
- possibly transmission mounts (removed mounts came with the car). I haven’t measured the gap but it looks good by eyeball and there are no vibrations usually associated with worn trans mounts.
- Le Douche Carbon Fiber look steering wheel. Factory steering wheel available for purchase separately in optioned color, it needs re-covered.
- GTS rear fascia and lights

Reach out with questions. Test drives in the San Antonio area, tour under the car, or specific testing requests are available with proof of funds.
- I have ~2000hrs on 928’s, I am happy to perform specific service/maintenance for the purchaser after the title has transferred at competitive rates but have limited availability thru MAY2025. I can quote TB/WB, intake refresh, reupholstery, etc. if interested after purchase (time permitting)
- this is a great driver quality 928 S4 that needs some interior work and minor cosmetic work to really shine.