Old thread

I had a few issues like this that haunted me at one point. A bad TPS was implicated in one instance, a bad coil in another. Neither were direct or easy to diagnose.

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My best guess is the IAC valve. I swapped out the crank sensor with new Denso, and it did improve but only slightly (sorry I forgot to update LOL!). I then put in an aftermarket IAC valve from the local parts store, and now it runs fine once it gets up to operating temperature. It still has the weird timing issue until it warms up, though. If you're going to spend money on the IAC valve, I would definitely pay the extra $ for a genuine Toyota part if that's an option for you. Do NOT waste your time or money on the cheap knock-off from Amazon (speaking from experience).

Just figured I'd update this post. Turns out my 4Runner has been doing "okay" for the last year or so, just with weird timing/idle issues until it warmed up to operating temperature. Then about a week ago, it started up, idled weirder than normal and I tried to give it a little gas and instead of revving up, it quit and wouldn't restart.

I finally pulled the ECU out from behind the glove box, and one of the capacitors was leaking (probably had been a long time from the looks of it). That may well have been my problem all along. So I ordered a rebuilt ECU from a vendor in Colorado that seems to have a good reputation. However, after plugging that in, it seems the aftermarket IAC valve I put in last year was toast as well, because it's making a weird buzzing sound I've never heard before... like the IAC cycling open and closed REALLY fast, with the ignition key turned to ON, with engine OFF.

So since I'm just throwing money at it now anyway with the ECU, I bit the bullet and ordered an OEM IAC valve and TPS, on solid advice from mtbtim and gamefreak to avoid aftermarket IACs and that the TPS could definitely cause it not to start, and the TPS I have in there is an aftermarket as well. The new parts will be here in a few days, and I'll continue this epic saga... LOL

Oh, the TPS is aftermarket too? That's a very vital sensor to be chancing it. I hope that does fix your issue.

Now I'm incredibly confused. I've got a rebuilt ECU from a reputable vendor, OEM IAC valve and OEM TPS. I've replaced the fuel pump, fuel filter, crank and cam sensors (both Denso), ECU coolant temp sensor, and the cams and crank all line up to TDC. It won't fire up, even with starting fluid spray. If the truck sits for a day or two, it seems like it will try to fire up for about 1 second then quits.

Still cranks but won't start, and the IAC valve is cycling open and closed really fast when the key is turned to "ON" (engine OFF). Pulling the EFI relay under the hood stops that, but the cycling happens even with a known good relay. Pulling the circuit open relay beneath the fuse box under the dash has no effect, still get the IAC cycling.

I've tried disconnecting sensors/parts to see if something is shorted out, each one individually: igniter, fuel pump, MAF, vapor pressure, ABS, cruise module, TPS, and I still get the IAC cycling with ignition ON engine OFF. I've checked every fuse, and they all appear intact (though I haven't checked them with a meter).

And for some reason, I can't get an OBD reader to connect to the ECU anymore (the original or the new one I recently put in), though the original used to work.

Any ideas would be most welcome!

It may be time for a very thorough wire inspection. Follow each sensor's wire loom back to the firewall and check for any sort of abnormal bends, old splices (you'll often see the connector still there) or blackening or splitting. After that, try opening up the ECU body itself. It's not hard to do and it's not all that fragile. Look for any damaged capacitors or burn marks. If you have a buddy with a spare ECU, try swapping it out.

You've covered all the big stuff but the inability to connect to the ECU is a big clue here.

Lastly, disconnect the battery ground to fender, passenger's side cylinder head to firewall and engine bay OBD-II port to intake plenum grounds, clean, and replace. Bad grounds do funny things.

Do you have power at your diagnostic port?


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Put a test light between terminals 6 and 14 of the OBD connector to see if you have power and ground with the key on. The EFI relay/fuse powers the OBD port and the relay is controlled by the ECM.

I did purchase a reman ECU, because the original one in there did have a leaking capacitor that buggered up several traces. I also took your advice and cleaned up the grounds, and I am able to get it started up momentarily with a blast of starting fluid now. PROGRESS! LOL **Edit: I should qualify this, that I do have to depress the throttle somewhat to get it to run... not wide open, but to hold it at about 1500rpm

Definitely some weird electrical things going on here...

I hadn't thought to check, so I just did now that you mentioned it, and... I do have power at the +B terminal of the diagnostic port, when I turn the key to "on" as Bad Luck mentioned.

I will check that as well. I do get +B power at the diagnostic port with the key "on"

So, continuing down this long, winding journey... I cleaned up the grounds as gamefreak advised. And here's a strange (to me) condition that is new.

If I disconnect the fuel pump from under the back seat, and I give a 2-3 second squirt of starting fluid behind the air filter, and give it enough throttle to hold at about 1500-1700rpm, it will start up and run (kind of rough, but it runs) for about 2 minutes (yes, minutes)... during that time, I get white smoke but it doesn't smell like oil or antifreeze being consumed. I am guessing that for some reason the cylinders are being flooded by fuel, and the starting fluid helps combust just enough that it will fire and consume a little bit of the liquid fuel, and once the liquid fuel burns off with the help of the starting fluid, it stops firing.

Once that comes to a stop (I'm guessing it's just running off residual pressure from the fuel line and the starting fluid helps to combust the fuel), I can give a squirt of starting fluid, and it will run for about 2-3 seconds, and during those 2-3 seconds it runs clean and smooth, what I would call "normal."

If I then reconnect the fuel pump, it runs for a few seconds then quits.

I can repeat this process: disconnect FP, squirt, runs for 2-3 minutes with white smoke, reconnect FP, won't run.

To me, it makes no sense. Can the fuel pump create too MUCH pressure and flood the cylinders?? Hopefully this might spark someone else's more experienced mind and point me in the right direction.

**Edit: just for reference, during experimentation today I cracked the fuel line at the tank side of the filter and ran about half a gallon out into a clear container, thinking maybe I just got some bad fuel last time I got gas. It's clean and clear golden gas color, no visible separation or settling, and doesn't smell off or soured.

Will it start and stay running with ether and the fuel pump relay.

You may just need to hold the throttle open and get it running and let it relearn it’s adaptives.

If you can, get it running and hold it at 1500rpm for a little. Then slowly back off the throttle and let it relearn its idle position.


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I was able to get it running on starting spray at 1500rpm for 2-3 minutes, but now I've got bigger problems. Looks like I'm getting coolant from behind the timing cover. Guess it's time to do the timing belt, pulleys & water pump job and/or head gasket. With 280K+ miles (100K that I put on it), I guess it's earned it

You can pull the exhaust studs out of the head and not need to remove the exhaust manifolds to pull the heads.


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