I had the exact same results on mine except it was cylinder 3 that was low.ZionXIX wrote: ↑21 Dec 2025, 11:08 Still trying to diagnose the rough idle condition.
The idle air controller is working, bench tested with the battery and made sure its clean.
Checked for vacuum leaks using a smoke tester. Found a huge gash in the hose between the turbo and intercooler. Sealing that opening with my gloved finger does nothing to the idle. I have a do88 silicone kit on order. Hopefully will be here before new years.
I pulled the spark plugs. They all look great. There are probably less than 10,000 miles on them. No cracks on the porcelin. The plug boots look new, replaced with bougicord about 8 years ago.
The distributor cap is super clean inside. Also replaced about 8 years ago with the plug wires.
I also cleaned the 2 ground wires on the back side of the valve cover.
Performed a compression test since I had the plugs out. Cylinder 1-4 are reading 150psi, cylinder 5 is at 135 psi. Maybe a valve job is in order?
My logic says if it was a bad fuel pump or low fuel pressure, the engine should perform worse at anything above idle as it would be starved for fuel. So I think the fuel pump is good.
For what it's worth I've had idle issues that were solved by double checking the vacuum routing and fix the fuel pump control module. (The forum will call it a "relay" but using the whole name is a hill will now die on since it's more than a simple relay)








