1994 850 won't idle but will rev, replaced MAF now no start

[RussB]

Run a compression test

Most=excellent advice. Time to start at the beginning

...make sure the engine isn't scrap before you spend another Pfennig.

what is the pfennig to dollar exchange rate these days?

[xterraguy]

Went out and monkeyed with it some more today. Looks like the MAF I nicked from the pick-and-pull isn't the same. It's a Bosch, looks similar enough to the one I started with, but the part number is not the same (can't even seem to find it) so I have the one it came with back in.

Wish I had been a bit more methodical but I can't remember the exact sequence I took today.

I pulled the airbox out, took off the IAC and checked the hoses for it for any leaks. IAC rotates freely when I twist it in my hand, no cleaning needed. I buttoned everything back up and got it warmed up again and it changed behavior. It would actually stay running on its own but would just rev up towards 2000 for a moment, stutter, and rev back up towards 2000, on and off like that somewhere between every 1-2 seconds. If I opened the throttle just a bit (like what would normally bring it up maybe 200 RPM), it would rev up to 4000 or so, but still sorta wanted wanted to "pulse" a bit.

I pulled codes and got 121 for the MAF as expected, but now I was getting 223 for the IAC valve. I'm pretty sure I introduced this code accidentally, maybe I hadn't fully plugged it back in at one point? Either way, it didn't return after clearing it, despite the new behavior persisting afterwards.

I tried disconnecting the MAF again and now it's back to the original behavior, and I can't seem to get it to start that pulsing idle again, even disconnecting the IAC deliberately. Only code is MAF again.

Argh, I'm really just about ready to take it to a shop. In the meantime, I'm gonna get a new MAF for it since I know this one is bad.

[abscate]

Being methodical is essential on these cars. It's a complex, intertwined engine management system that delivers incredible efficient, powerful, and clean performance, but you cannot 'Wing it' when you troubleshoot