Cornerlot

I'm a novice at the 928 game, mostly aircooled 911 stuff for me. I've acquired a 1988 928 S4 that's been off the road for several years (with gas drained). Its starts up fine on fresh gas, but doesn't like to rev easily off idle by going flat or stalling without a very very gradual throttle application. It will stall if you put it in gear (auto) or release the throttle from off-idle RPM's. I'm thinking fuel pressure. I have a CIS pressure kit that I could start with, if it will work, so where and what should I check? I haven't pulled off the fuel rail covers yet, but isn't the test port on the front of the passenger fuel rail?

Advice appreciated..

Speedtoys

You're already ahead of the game. but doubtful that setting pressures will resolve it.

Probly best to jump straight into new injectors, and fuel system hardware (reconditioned, etc).

Tom. M

Sounds a lot like a failed MAF. Can start/idle, and can run at around 2500 rpm, but a dog otherwise. Disconnect the MAF and see if it still acts the same. If so, perhaps a new MAF will help.

Speedtoys

That wont work unless you unplug the MAF first.

A bad maf wont operate outside of the starting circuit. ~2 seconds.

Mrmerlin

Based on your report the LH computer needs to be rebuilt,
I would also get the MAF rebuilt,
and replace the 02 sensor with a factory part ,
and replace the temp 2 sensor and its connector.
Inspect the CPS and replace it if the connector crumbles.
if you have to replace the CPS then you probably need an intake refresh,
please post engine pictures.

GUMBALL

Check with Richard at Electronik Repair (electronikrepair.com)

He does exchange rebuilds on ECUs as well as MAF.

Tony

Where in TX...there is a pretty great group there that you may be able to swap known good parts with...ECU..MAF etc.

Cornerlot

I'm in New Braunfels.

Cornerlot

Anyone is welcome to stop by with trial parts, before I blindly take the plunge to get the MAF and LH rebuilt. Car shows 144k, actual is not too far off that.

More details;
Foot off the gas it starts but normally stalls. Pump is running at startup.
Foot slightly on the gas it starts and idles at 2000+, and will rev to 6000 if the accel is depressed gradually (in neutral or park).
After a few minutes of maintained high idle is will idle down (in neutral) on its own at about 500 - 600 RPM but stubbles if revved.
Putting in gear (auto) at any RPM its a struggle to keep it running.

Mrmerlin

Please understand both of these parts must work perfectly for the engine run.
and if they are old then this service is part of keeping the engine running perfectly
The LH chips fail from a time perspective, this means every LH will need to be rebuilt
the MAF internals also fail from old age. This means the MAF will go out of spec and need to be rebuilt