Land

87 22rte 4Runner with (I think) a 5-speed swapped in.

Since I got it a couple months ago, it's intermittently had trouble idling. Would misfire and die without gas. Warm or cold, didn't seem to matter. Sometimes it would run just fine, with idle rock solid at about 900-1000.

Lately, the miss and poor idle (really a non-idle) has gotten worse and more frequent, to the point that one time I couldn't get it started, not even by push starting. So, I decided to put some more time into diagnosis and fixing it.

I replaced the plugs, plug wires, redid the injector splices, replaced the intake plenum gasket and throttle body gasket and most of the vacuum lines. Also adjusted and tested the TPS and AFM per the FSM and had the injectors cleaned and balanced. Adjusted the valves and did the ignition timing when I first got it too. Still, it wouldn't idle.

Put a paper next to the tail pipe and, sure enough, it gets sucked against the pipe intermittently. Seems to smooth out a little bit with throttle, but it definitely doesn't run totally smoothly.

Before I tear into the head, could this be anything other than a sticking or burned exhaust valve (or two or three or four)?? Is there anything else I should try? Can I be sure that I will fix the problem with a new head/valves/etc?

DonHagen

I think you definitely have some valve problems here. Unless your exhaust somehow has a venturi vacuum somewhere, your engine is pulling air into one of the pistons from the wrong place.
Do you have something loose inside your intake that's fluttering and plugging it up? I would follow the path air takes into your engine. Visually check inside every pipe and connection right into the intake manifold. Do the same test but on your intake. Remove the air filter and run it. Don't worry about no filter. Dragsters race without them and don't blow up. As long as you don't forget to put it back on or drop your watch in, it's fine. With your hand can you feel air being pushed out intermittently?
You can narrow the problem down to either intake, exhaust or right in the middle.
If you don't find anything, do a pressure test. You can buy the spark plug adapter and gauge from harbour freight or princess auto. A haynes manual can walk you through the procedure. You seem to know your way around a tool box, I think you'll figure it out. Good luck, this is an interesting one.

jennygirl

Some other ideas:

Try a leak down test and also check for blow by? That way you can narrow down to FI system or internals.

Checked the idle air control valve? Those hybrid mechanical-electrical blunders are known to get gummed up / fail on pre-89 22re's. Gave me tons of headaches on my non-turbo until I swapped for the later model plenum+TB w/ purely mechanical IAC. It can create some annoying intermittent problems.

Hope you find it! I feel your pain, chasing idle issues on these motors is classic headache material.

Land

Yep, checked out the IAC while I had the plenum off, seemed ok. Resistance was fine and the door moved around when I put it in the freezer. Looked clean and seemed to turn smoothly to my touch.

Given that I've checked many things idle-related already and haven't really found an obvious problem or fixed the issue, I'd actually feel better knowing it's a valve issue for sure. A known big problem can be better than a small gremlin that's impossible to track down.

Next step is definitely a compression test/leak down test, I'll report back with the results when the time comes.

DonHagen described a super sensible procedure there, given that I'll have to follow those steps to get the head off anyway, I might as well do some careful inspection on the way.

Replacing the Throttle Body with a later model one with built in IAC sounds like a good option, I suppose I can track that down in a build thread? The fewer old crusty hoses and strange bimetal actuators the better....

Thanks for your help!

jennygirl

I have a writeup on it in my sig

You're welcome, hope you figure it out

Land

Attached is a photo of my spark plugs that I pulled for the compression test. From bottom to top it's cylinder 1,2,3,4.

Compression test seemed to show around 105-110 psi on all cylinders. I suspect such a consistently low reading might be due to a poor seal on the testing tool, so I'll have to investigate more fully.

Curious what is going on with the plugs though, they are new, maybe 100 miles on them if that. Injectors were cleaned and balanced after putting in the new plugs.

Land

DonHagen

Wow, that's crazy! To have a pipe that long alternate between pressure and vacuum in pulses that quickly is really weird. It's moving a ton of air in the wrong direction. You must have a valve that's stuck right open or maybe just bent and binding slightly. Your compression test might not have shown it stuck open because when you turn the crank by hand the valve could easily keep up. Running, the valve might be lagging behind when it's closing and gets overrun.