Idle fine, then drop so low it quits, then all is fine.

Hotshot · Hotshot's Garage

Was with friend picking up his 86 930. Drove 2 hrs home with no issues. We knew that there’s an issue with it loosing power on long shifts. Still no issues.

Get home, start it up again, and she revs erratic and such low idle it quits.

Wait a few minutes, start up, she purrs idle for 3 mins ( 1.5-2 bar, 1100rpm ). Then out of nowhere, goes erratic and low to the point of cutting out.

Not a turbo expert.. just a NA owner.

Thoughts?

Warm up reg?

DaytonaCoupe66 · 03-10-2021, 03:07 AM

Could be a lot of things. Suggest testing the fuel pressures to start, and record the outputs. There's a ton of great diagnostic guidance on the turbo forum if you do a search. Start with the easiest, which is putting a fuel pressure guage on the car and testing the specs against the book. Post the results in the turbo forum and you'll receive suggestions on next steps.

Hotshot · Hotshot's Garage

We have the book, so this is a great starting point.

kach22i · kach22i's Garage

Start with the easy stuff like finding vacuum leaks.

jpnovak · 03-10-2021, 07:24 AM

Check:

Fuel pumps (There are 2 on CIS 930)
Check fuel pump relay - Do the mod to put single relay on each pump. Currently one relay driving 2 pumps
Check fuel tank screen for debris - Clean/change as necessary
Check fuel filter assembly.
Check Control puressures
Upgrade to Leask Adjustable WUR
Setup Control pressures with new WUR

Enjoy the boost.

motorracer · 03-10-2021, 05:17 PM

I think you mean fuses they have to relays already.

DaytonaCoupe66 · 03-11-2021, 03:20 AM

Quote:

Originally Posted by Hotshot

We have the book, so this is a great starting point.

You've got to start somewhere and all suggestions you receive will have merit. Be sure to keep a journal of what you're checking. I had chronic symptoms similar to yours but without a high idle. All CSI diagnostics were within spec, so I could put that aside as a likely culprit. I rewired the two fuel pump relays with separate fuseable links directly from the battery (as per the fix advocated by many on the turbo board) and resolved my issue for $7 in parts and 30 minutes of time. But...not before I sprung for a new rear fuel pump and rebuilt CDI. Sometimes you'll get lucky!