Rough idle fix
07-13-2006, 03:18 PM
#1
Instructor
Thread Starter
Join Date: Dec 2005
Location: Silver Spring, MD
Posts: 124
Likes: 0
Received 0 Likes
on
0 Posts
Rough idle fix
FWIW. My '88 S4 auto (73,000 mi.) started showing all the classic rough idle symptoms. Ok start @ 1000 rpms. Then, as engine warms and revs drop, idle wanders, finally hunting between 300-500 rpms. Sometimes stalls. Exhaust smells rich, but no black smoke at start up. After many searches of the voluminous threads and suggestions, I checked the standard things:
Vacuum: all hoses/connections were tight and flexible.
ISV: New one by PO @ 60,000 miles. Tried WD-40 soaks without success.
MAF: I installed new one several months ago (from John Speake).
Temp II sensor: correct resistance at terminal 2.
Plugs: sooty but not oily.
Coil wires: bright, clean.
LH relay: substituted new one; no change.
So it looked like a failing LH brain. But Rich Andrade at Electronikrepair, who had contacted me about an LH refurbish, said to check the Fuel Pressure Regulator before shipping the brain. I pulled vacuum there with the MityVac and found it wouldn't hold pressure. I also detected some gas odor. I also pulled vacuum on the fuel pressure dampers and they held fine. With a new FPR from 928 Intl installed, the engine idles per specs!
So, many thanks to Rich and the others who helped.
Vacuum: all hoses/connections were tight and flexible.
ISV: New one by PO @ 60,000 miles. Tried WD-40 soaks without success.
MAF: I installed new one several months ago (from John Speake).
Temp II sensor: correct resistance at terminal 2.
Plugs: sooty but not oily.
Coil wires: bright, clean.
LH relay: substituted new one; no change.
So it looked like a failing LH brain. But Rich Andrade at Electronikrepair, who had contacted me about an LH refurbish, said to check the Fuel Pressure Regulator before shipping the brain. I pulled vacuum there with the MityVac and found it wouldn't hold pressure. I also detected some gas odor. I also pulled vacuum on the fuel pressure dampers and they held fine. With a new FPR from 928 Intl installed, the engine idles per specs!
So, many thanks to Rich and the others who helped.
07-13-2006, 05:35 PM
#2
Addict
Rennlist Member
Rennlist Member
Originally Posted by rmr25
FWIW. My '88 S4 auto (73,000 mi.) started showing all the classic rough idle symptoms. Ok start @ 1000 rpms. Then, as engine warms and revs drop, idle wanders, finally hunting between 300-500 rpms. Sometimes stalls. Exhaust smells rich, but no black smoke at start up. After many searches of the voluminous threads and suggestions, I checked the standard things:
Vacuum: all hoses/connections were tight and flexible.
ISV: New one by PO @ 60,000 miles. Tried WD-40 soaks without success.
MAF: I installed new one several months ago (from John Speake).
Temp II sensor: correct resistance at terminal 2.
Plugs: sooty but not oily.
Coil wires: bright, clean.
LH relay: substituted new one; no change.
So it looked like a failing LH brain. But Rich Andrade at Electronikrepair, who had contacted me about an LH refurbish, said to check the Fuel Pressure Regulator before shipping the brain. I pulled vacuum there with the MityVac and found it wouldn't hold pressure. I also detected some gas odor. I also pulled vacuum on the fuel pressure dampers and they held fine. With a new FPR from 928 Intl installed, the engine idles per specs!
So, many thanks to Rich and the others who helped.
Vacuum: all hoses/connections were tight and flexible.
ISV: New one by PO @ 60,000 miles. Tried WD-40 soaks without success.
MAF: I installed new one several months ago (from John Speake).
Temp II sensor: correct resistance at terminal 2.
Plugs: sooty but not oily.
Coil wires: bright, clean.
LH relay: substituted new one; no change.
So it looked like a failing LH brain. But Rich Andrade at Electronikrepair, who had contacted me about an LH refurbish, said to check the Fuel Pressure Regulator before shipping the brain. I pulled vacuum there with the MityVac and found it wouldn't hold pressure. I also detected some gas odor. I also pulled vacuum on the fuel pressure dampers and they held fine. With a new FPR from 928 Intl installed, the engine idles per specs!
So, many thanks to Rich and the others who helped.
Bob,
Glad to have helped. Another 928 back to running well!
Rich
