Blamalam

Hi guys,

I've been a long-time lurker, so let me start off by saying "Thanks!" for all the collected wisdom on this forum--I had the page pulled up on my laptop as I went through a timing belt/water pump change on my '94 4Runner with the 3vze. The truck had been dripping coolant after shutoff, about a cup or so each time. Sadly, it's still dripping coolant...but that's not the reason for my post.

I CAN'T GET THE DARN THING TIMED. My idle is WAY off--250-500 RPM, and it'll stall if you leave it alone. Give it some gas and it revs right up--in fact, it's driveable as long as you pop it into neutral at red lights and give it just a touch of throttle. Having said that, it's idling incredibly rich, almost to the point that the fumes burn my eyes.

Here's what I'm seeing:

• Unstable idle, will stall
• Jumping TE1 and E1 (or whichever the diagnostic ports are, I can't remember right now) has no effect on idle speed
• No codes
• Timing light jumps between 10 and 20 (? About 2 inches "up" from the 10 degree mark on the crank pulley.
• Persistent miss at idle and part throttle

Here's what I've done over the past month-plus:

• Water pump and thermostat.
• New timing belt--assembled everything, rotated assembly with breaker bar on crank bolt through two complete turns and all marks matched up
• Valve adjustment. I couldn't get the SST to work, so I wound up pulling the cams. That made a tough job MUCH easier. With the cams out, I cleaned everything I could see to clean. New valve shims adjusted to be on the loose end of spec (.013) for the exhaust, and right in the middle of spec (.009, IIRC) for intake. Unfortunately, this step required that I remove the distributor.
• All manifold vacuum lines replaced with new tubing
• Throttle body and intake plenum cleaned. I did not remove/clean the IAC.
• VAFM replaced with a junkyard unit--original failed FSM DVM tests (never threw a code)
• Replacement TPS switch--original failed FSM DVM tests (but never threw a code)
• Checked intake air tube for cracks/leaks, none found
• Plugs cleaned and re-gapped. Plug wires look to be fine.
• Verified spark to all cylinders by pulling plug wire at distributor cap just enough to create a gap for a spark to jump across (only got shocked once!). The idle dropped a little bit each time I pulled a plug wire.
• Verified proper EGR function by pulling vacuum on EGR at idle--idle sagged and the engine nearly stalled
• Ohm'd fuel injectors, all of which were replaced about four years ago. They all checked out, right in the middle of spec (can't recall the reading, sorry)
• Ohm'd ECT sensor without engine running. Reading was right in between the 68 degree and 100-whatever degree spec, so I called it good.

I've given this thing my weekends for the past two months, and since it was due for a safety inspection I dropped it off at my mechanic's and asked him to check my work at the same time. He couldn't find anything wrong, but also couldn't track down the cause of the miss. He said he verified that the TPS was adjusted properly, but from what I've read a faulty or improperly adjusted TPS will show up as no change in RPM when test ports are jumped (if that makes sense). If I unplug the TPS, the idle RPM goes up.

Just as an aside, the engine has 183,xxx miles on it, and the HG recall was performed around 110k (previous owner). I have no evidence of HG leaks--no bubbles in coolant, not using coolant (besides what winds up on the ground after I shut off), the oil isn't milky. I did the "dollar bill" test at the tailpipe for a burnt valve, and it passed. I'm still going to perform a compression test, and I guess I need to re-check the TPS sensor. Any other suggestions?


Sorry for the huge first post, thanks for all the help.

Blamalam

I figure since this thread has had a few views and no responses that other folks are working through similar issues. I'm still going 'round and round with this frigging thing--see https://www.yotatech.com/forums/f116.../#post52284864 .

I restabbed the distributor today thinking I might've been a tooth off--nope, same issue: won't idle, wants to die. I unplugged the TPS, truck died. I unplugged the VAFM and the idle surged WAY up--1500 or so. I have a junkyard VAFM and I've installed that, so it will actually keep running now if only briefly. I've rechecked vacuum lines, and sprayed carb cleaner around the passenger side of the intake manifold (vacuum hell). I noticed that the brake pedal is rock hard, which is new. The pedal doesn't go down under pressure and the brakes are weak as hell, so I guess I have a manifold vacuum leak.

Hopefully this info helps others if only by process of elimination.

Blamalam

More info:

• no error codes
• idle surges between 200 - 500 RPM, I can watch the throttle opened move back and forth under vacuum at idle
• throttle body is clean
• no air intake leaks
• I can hear backfires under the intake when giving it gas
• All new small (4mm) vacuum lines, hooked up correctly per multiple different vacuum diagrams and confirmed with pics of properly hooked up engines from multiple sources
• Mechanic can't figure it out either
• Engine will die if I put truck into gear unless I blip the throttle
• Cooling system burped

AKHeathen

are you saying the idle is 2-500rpm? the starter cranks it in that range. it should be like 600-750 warmed up most of your problems could be caused by a low idle. 2nd: replace the plugs. you only cap new plugs, after that they have been heat conditioned and gapping them could pop an electrode, causing piston or valve failure. ngk is highly recomended. os the 10-20 timing thing based on a surging idle, ot does it scatter like that? the dampener can come loose. i've seen it just sit there and slip, making it impossible to time (i did it by feel that time) and when i replaced the dampener, it simply spun freely on the inner hub it used to be glued to.

Blamalam

Thanks for the reply! Yeah, after starting the engine it will hit 1,000 -1,200 RPM for roughly 10 seconds then drop down to 250-500 (indicated), then stall. The plugs are new (should've mentioned that) NGKs. I can't get the idle set correctly to set the timing.

I posted in another thread that I've replaced the TPS sensor three times, and each of the three tested out of range (approx. 5k ohms) for the idle reading (should be below 2.3k), including one sourced from a dealer. I've loosened all the throttle body stop screws so that they're not contacting their associated swing arms, and I've made sure that the butterfly valve isn't binding up in the TB throat--it isn't, and it's closing fully. I don't feel the dampener moving at all.

AKHeathen

turn the idle up to spec first, then set the timing at proper curb idle. after timing, you might end up turning it back down and re-checking the timing again, but trying to set the timing at rpm's other than specified will change it greatly.
continue adjustments after that.

Blamalam

I've adjusted the idle screw on the throttle body almost completely out and the idle still won't go up to a steady 800 +/- 50. I thought the ECT was dry, so I burped the cooling system and still no improvement. The engine is running rich and misfiring, and I know that the cam timing is right. I pulled and restabbed the distributor but still can't get it to idle right.

AKHeathen

can you unplug the cold start injector and see what it does?

Blamalam

I tried that early on, no change. The only change I do see is when I unplug the TPS (I might've mentioned that in my other thread, can't remember) the idle goes up to around 1,600 or so then settles back down, and then the engine dies.

AKHeathen

which screw are you adjusting?

Blamalam

Idle adjust screw on throttle body. From the front of the truck, it's facing you just behind the dashpot.

AKHeathen

make sure the bypass air passage didn't get plugged and that the vsv is working.

Blamalam

You mean the bypass air passage in the TB going to the IAC valve? That's clear--I've had the TB off several times now, so it's spotless :-)

I'm going to check the VSV today--I spent yesterday tearing everything off the front of the motor to verify (for the third time!) that my timing marks line up. I also ran a compression test and got some screwy numbers (all 175 - 190, which can't be right) that I'm chalking up to a cheap gauge. If nothing else, at least I don't have a dead cylinder--I'd tried pulling the plug wire to each cyl during earlier testing and the miss/misfire isn't restricted to one cyl. I also checked coil resistance, ECT resistance, and plug wire resistance--all passed.

AKHeathen

i meant the passage in the throttle body from the idle screw to in front of the throttle plate.

Blamalam

If I had a brain I'd have seen that. I can just take that screw out all the way, eh? I'll give that a shot--I really appreciate your help!

AKHeathen

just watch out for the spring. it should have one. as a precaution, i always throw down a paper towel or to to catch things.

Blamalam

Just to circle back, my idle/misfiring issues have been solved--it was the EGR VSV. The VSV had failed open, which allowed the EGR to pump exhaust into the intake at idle.

Thanks for the help, everyone!

AntonioCm1983

Rpm should be between 730 to 978 on the 4runner

AntonioCm1983

try checking the pcv on the valve cover also check the purge valve on the brake booster and the vsv could also be bad on mine found the charcoal canister itself went bad hope this helps it's about 99 percent of the time never the gas cap like ever

TNTye

Could be your Ecm mine had failed and some similar issues. Timing jumping around rough idle stalling