Rough idle, running super lean

Okay after about a year of work I finally got the ST185 running again today, and to my dismay, it's still having the same idle issues as it did when I started taking it apart. It idles super rough/low, at around 700-800 RPM. What's new is that with my new AEM wideband AFR I can see now that it's running lean. Very lean. At idle it's off the charts >= 18:1. When I give it some gas and bring it up to around 3k RPM it's hovering around 15-16, still way too lean.

In the year that I've had it apart I've replaced every vacuum line and intake hose, plugs, wires, intercooler, sensors, and rebuilt the turbo. Whatever it is, none of that has made a difference. I'm about at my wit's end here as I've sunk more than double the value of the car into troubleshooting at this point... any ideas?

If the engine is misfiring, for whatever reason, there will be excess oxygen in the exhaust. This will cause wideband O2 meters to report a lean condition.

Look for things that cause misfires like dirty fuel injectors, or ignition system issues such as a weak coil.

___Scott___":3k0ivbvb said:

If the engine is misfiring, for whatever reason, there will be excess oxygen in the exhaust. This will cause wideband O2 meters to report a lean condition.

Look for things that cause misfires like dirty fuel injectors, or ignition system issues such as a weak coil.

Click to expand...

I guess I can check the coil but for the most part that all sounds like the engine is coming out. It does have a sort of lope to it although prior to going over all the vacuum tubing and replacing everything I just assumed the black magic vacuum operated auto idler was on the fritz. Now I'm concerned it may be a compression problem, which effectively means a new motor....

was really hoping I was finally done with this, or that it could at least be a simpler fix... :shrug:

Have you replaced the fuel filter? I was working on a 87 Toyota pickup and I installed a wideband sensor to adjust the carb. It was beyond 18.0 idling because of the fuel filter. I replaced it and that helped bring the afr's way down

Yeah there are so many things it could be its hard to pinpoint.

Things I would check;

Vacuum leak after the AFM or bad AFM
Compression
Injector impedance (ohms)
Spark gap
Voltage drop from alternator
Distributor cap and rotors ignition coil.
Base timing
ECU capacitors, our cars are old and these things are leaking more often.

Have you checked your ISC valve? These control idle. They over time can carbon up and prevent the shaft from turning properly.
Thus the little butterfly valve is not opening properly giving rough idle or staying open a bit allowing un-metered air into the manifold.
Check the electrical plug, that the elect. solenoid is working ok and or clean out the carbon deposit.

Also, check

- map sensor. It might be reporting low pressure forcing the ecu to release less fyel
- each injector with a stethoscope to see they are all firing
- clean the throttle body and butterfly, it may not be closing completely.
- check the cold air valve, it could be stuck open.