Originally Posted by carringb
I would describe the o2 sensors as calibration devices, rather than control devices. They are relatively slow responding, which is why an upstream problem with fuel or air will cause surging while the o2 sensors respond.
The primary control is the MAF. There's various way to troubleshoot, and the Ford method has to monitor the 02 signals are varying RPMs. If the lambda value varies at low RPMs, but not at higher rpms, than there's a vacuum leak introducing a little extra air. If it varies at all RPMs, there's probably an intake leak downstream of the MAF. If it only leans out at high RPM, then fuel pressure become suspect.
I'm gonna read that a couple times and see if my scan tool can pick up these Lambda values.
BUT I did do the JSweezy method and I think it's running much better.
Pulled the intake off and cleaned out and cleaned up the throttle. Cleaned the intake and cleaned the PCV intake tube. Spent a good amount of time tracing some of the vacuum hoses so I have a mental picture of some stuff I still need to check. Cleaned the MAF again, why not?? Cleaned all the intake rubber fittings etc. Repaced them very carefully and snugged them nicely. Repaced the PCV valve and tube with new ones. Old ones were probably fine, so that might be the parts I threw at it. I am cool with 40 bucks.
Restarted the van and and did the idle rev, it dipped to 400 as usual and felt like the motor would stall because it goes quiet. It will catch itself and then go back up to 600.
So then I pulled the neg cable and turned on the lights and ate some dinner. This should have reset the KAM. Which it seems to have done. Made sure everything was off and then put the neg cable back on. Turned the key and watched the CEL light until it blinked and then went back to lit. With everything off I started the engine and watched it idle. It went to about 1200 and then slowly made it's way down to 700 and then 600. Let it sit there for 5 minutes then turned on the AC and sat for a couple more. Turned off the AC and went for a 15 mile cruise around town and on the highway. Kept it mellow for the first 10 but did push it to 75 on the freeway.
So the immediate differences were that the van coasted a little better. The RPMS still dive but not like before. When coming to a stop or slowing around a corner the van would feel like it would go dead for a second, but now i just see a very quick dip to 400 and recovery back up to 600. Feels much better on that end. I tried the idle rev trick again and it won't let itself drop below 600, so that issue went away. All in all behaving much better.
I am still wary that there could be a rogue tune in there from the previous owners. When I get a tuner, I will first get the van reflashed so I have a base stock tune. Still some things to check over for vac leaks, but I think I have moved things forward for sure. I would like to check my scan gauge again and check those fuel level trims when I do the idle rev. also will look around in it to see if I can find the 02 sensor operation in the scanner.
As always I am very grateful to everyone here for helping me out and teaching me a thing or two. Not sure I would even have a Van at all if I hadn't stumbled on this place and caught the fever. The big investment is not so intimidating with all the folks here having my back when I grab a wrench and try to make some things right.