ToyotaViejo

I've got a '90 3VZE 4Runner 5 speed, and I had an intermittent low idle problem, and I wanted to pass along my solution.

At idle speed, the engine would drop to somewhere around 400rpms after it had warmed up. Further, after starting and stopping the engine a few times while warm (running errands) it would often idle very low. After turning on and turning off the A/C, it would also idle low. On a cold start, it was a champ.

The truck came with a TPS that passed all but one of 4Crawler's diagnostic tests. I replaced it and calibrated the new one with the throttle body out of the truck. It solved a miss on acceleration, but did nothing to affect the low idle.

I replaced the O2 sensor because the exhaust smelled really rich. My emissions numbers improved, but there was no change in mechanical operation.

There were no vacuum leaks, and all the lines were fresh and supple.

I also pulled the idle adjust screw, cleaned it and replaced the o-ring. The old one was totally hardened.

I tested the EGR modulator per the FSM and cleaned the filter. I also tested the EGR. The modulator was dirty, but functioned normally. At the same time, I checked my ignition timing. I had previously replaced the distributor for an unrelated problem.

When I installed the new distributor, I advanced it a bit to 12BTDC to squeeze a little more power out of the engine off the line.

The timing light showed that after 6 months, the timing was still 12BTDC, so the distributor didn't move; which I thought it might have.

I clocked it back to the factory 10BTDC, pulled the EFI fuse to reset the computer, drove it for 30 minutes to get it good and warm, and then set the idle screw with the diagnostic jumper in to 800rpms.

A month, and a few long road trips later, the truck idles fine under all conditions.

I find it a little hard to believe that a mild ignition advance was the sole culprit, but I think it took an old and imperfect system past the limit where the computer could sufficiently adjust the system to maintain an in-spec idle.

My understanding is that the only timing/ignition control the computer has is the advance. I suspect that the baseline advance was set too high, causing a rich state at idle that caused the computer to cut fuel flow at the injectors and/or over-retard the ignition.

I'm running 10w30 on 87 octane winterized gas, and get 15-16 in city driving, 17-18 on the highway (75mph), and even got 20mpg on a long, downhill run from Flagstaff to Phoenix a week ago. I shift at or below 2500rpms, and it's geared 4.56 final drive on 31x10.50s.

It leaks oil like the Exxon Valdez; mostly from the valve covers, but a little from the pan. The PO used a paper gasket on the pan that seeps a little.

All that aside, check your ignition timing, and if all else fails, set it back to 10BTDC. A lot of folks on this board recommend 12-14BTDC. For me, that didn't work.

MudHippy

I've run mine @~20° BTDC before on 87 octane, and it idles just fine @ 800 rpm. I currently run it @ ~24° BTDC on 92 octane, and it idles just fine @ 800 rpm like that too.

So you think you're having a hard time believing it? I'd say it's not even possible that's the case.

There's probably something not quite right with your ignition system. That's my guess. How do your plugs and wires check out? What about the ignition coil & ignitor?

If that's not it, then there must be something else going on with the engine. Because you should be able to run your 3VZ-E with the base ignition timing advanced quite a bit more than 10° BTDC without any problems.

ToyotaViejo

The plugs were new in September (NGK, properly gapped), and the wires were new in June right before I bought the truck. PO had a receipt. They're Bosch wires, but they don't show any evidence of leaks in the dark, and they don't have any burns from the exhaust manifolds.

When I pulled the plugs in September, they were in good condition, and probably not even de to be changed, but I did anyway.

I tested the igniter per the FSM, and it seems to be in spec. The coil either works or doesn't, no?

Further the truck doesn't show any evidence of a leaky windshield, and the ECU doesn't appear to be damaged or rusted from exposure.

The only other thing I can think of is that the process of removing the EGR and modulator unstuck something that was jammed. I could be wrong, but it didn't feel like a stuck/malfunctioning EGR. It felt like the engine was going to stall, but not like it was choking.