Rough idle - my fault, but I don't know what I did (2 Viewers)

[CharlieS]

Mea culpa. I changed a lot of stuff at once and am the root of my own problem. But, I don't know what I did to cause it...

Before I forget - it is a '94 1FZ-FE with 297k miles.

My idle is low and lumpy and i don't know what to troubleshoot.

I just got this rig in late spring, I changed the oil drove it about 50 miles before I tore into it.

I did the following:

factory parts​

• air filter
• oil filter
• valve cover gasket, spark plug tube seals, fipg
• spark plugs (gapped and torqued to spec)
• cap
• rotor
• distributor o-ring
• thermostat, gasket and water neck o-rings
• fuel filter
• gas filter
• coolant hoses 1, 2, and 3
• crankcase vent hose
• pcv valve, hose and gasket
• vacuum line to fpr (direct from gas filter)
• fuel return line
• PHH and hard line

I deleted

• egr valve removed and temp probe bypassed with huddexpo jumper, home made block off plates new factory gaskets, removed egr pipe
• pair assembly
• all vsv related items, capping all unused ports
• intake manifold coolant lines, capped with silicone caps and clamps at head and water pump

I changed

• wrapped engine harness with reflective fiberglass insulated wrap
• relocated O2 sensors, with new denso O2s and shaved alignment plugs, into exhaust manifolds with new studs and gaskets
• Capped the air intake where the PAIR heimholtz box mounted.
• Use the 96-97 water bypass hose (aftermarket) with factory gasket
• Bypassed the rear heater assembly with Wit's End kit
• 95-97 single line gas filter on head, direct vacuum line to the fuel pressure regulator

I filled with distilled water, made sure it was good.

Once it was warmed up, I jumped the DLC and set the timing to 3 deg BTDC.

I'm not getting any codes when I jump the DLC. I was getting 25 and 26 prior to swapping O2 sensors and resetting by pulling the fuse.

It starts right up and if it is cold, idles like a champ. If I turn the AC on, it boosts the idle up nicely.

But, after a minute (roughly?) the idle starts to drop off and it runs very "lumpy" (like it has a hot cam), progressively getting lower and lower until it is bouncing between 100-200 rpm then it stalls or I shut it off out of mechanical sympathy.

Once it is warmed up, if I start it, it immediately goes into stumble mode, like 800 rpm and slowly bounces its way down to 2-300.

If I give it some accelerator it seems happy to run with gusto.

I'm sure this is wrong, but it feels as if it is going from open loop to closed loop then starving for fuel and then it runs out and stalls, but I can't wrap my head around how that would be. More likely a vacuum leak, broken wire or damaged sensor(s).

All of my vacuum caps and block off plates seem to be where they should be.

Any troubleshooting guidance. I suppose I need toget back to basics and check fuel pressure and spark.

 

[OffRoadScott]

Mea culpa. I changed a lot of stuff at once and am the root of my own problem. But, I don't know what I did to cause it...

Before I forget - it is a '94 1FZ-FE with 297k miles.

My idle is low and lumpy and i don't know what to troubleshoot.

I just got this rig in late spring, I changed the oil drove it about 50 miles before I tore into it.

I did the following:

factory parts​

• air filter
• oil filter
• valve cover gasket, spark plug tube seals, fipg
• spark plugs (gapped and torqued to spec)
• cap
• rotor
• distributor o-ring
• thermostat, gasket and water neck o-rings
• fuel filter
• gas filter
• coolant hoses 1, 2, and 3
• crankcase vent hose
• pcv valve, hose and gasket
• vacuum line to fpr (direct from gas filter)
• fuel return line
• PHH and hard line

I deleted

• egr valve removed and temp probe bypassed with huddexpo jumper, home made block off plates new factory gaskets, removed egr pipe
• pair assembly
• all vsv related items, capping all unused ports
• intake manifold coolant lines, capped with silicone caps and clamps at head and water pump

I changed

• wrapped engine harness with reflective fiberglass insulated wrap
• relocated O2 sensors, with new denso O2s and shaved alignment plugs, into exhaust manifolds with new studs and gaskets
• Capped the air intake where the PAIR heimholtz box mounted.
• Use the 96-97 water bypass hose (aftermarket) with factory gasket
• Bypassed the rear heater assembly with Wit's End kit
• 95-97 single line gas filter on head, direct vacuum line to the fuel pressure regulator

I filled with distilled water, made sure it was good.

Once it was warmed up, I jumped the DLC and set the timing to 3 deg BTDC.

I'm not getting any codes when I jump the DLC. I was getting 25 and 26 prior to swapping O2 sensors and resetting by pulling the fuse.

It starts right up and if it is cold, idles like a champ. If I turn the AC on, it boosts the idle up nicely.

But, after a minute (roughly?) the idle starts to drop off and it runs very "lumpy" (like it has a hot cam), progressively getting lower and lower until it is bouncing between 1-2k rpm then it stalls or I shut it off out of mechanical sympathy.

Once it is warmed up, if I start it, it immediately goes into stumble mode, like 800 rpm and slowly bounces its way down to 2-300.

If I give it some accelerator it seems happy to run with gusto.

I'm sure this is wrong, but it feels as if it is going from open loop to closed loop then starving for fuel and then it runs out and stalls, but I can't wrap my head around how that would be. More likely a vacuum leak, broken wire or damaged sensor(s).

All of my vacuum caps and block off plates seem to be where they should be.

Any troubleshooting guidance. I suppose I need toget back to basics and check fuel pressure and spark.

View attachment 3383614

When you did the harness did you check for exposed wires in the harness? Also it appears there is a plug with no home, tan plug in the picture near the IAC.

 

[CharlieS]

I didn't check for damaged wires. The factory wire wrap is still intact. The heat protection is velcro, so I just peeled it back for the above picture.

The loose plug is for the no longer there vsv stuff.

 

[OffRoadScott]

View attachment 3383652I didn't check for damaged wires. The factory wire wrap is still intact. The heat protection is velcro, so I just peeled it back for the above picture.

The loose plug is for the no longer there vsv stuff.

View attachment 3383648

Mine was intact too but I had a short in the harness. Try moving the harness around while the LC is running and see if there are changes?

 

[OffRoadScott]

Also have you checked the injector clips, knock sensors clips tend to break too.

 

[CharlieS]

I just tried moving any and all harnesses in the engine bay and no change in behavior.

 

[CharlieS]

Mine was intact too but I had a short in the harness. Try moving the harness around while the LC is running and see if there are changes?

I will absolutely check all of this, but why would it run great in open loop cold start if the injectors were an issue. The knock sensor I could see how it would be ignored in open loop and then seen in closed loop.

 

[CharlieS]

I couldn't swear in a stack of bibles, but a visual inspection with a mirror on a stick and flashlight looks like injectors and knock sensor plugs are intact and in place.

 

[OffRoadScott]

I will absolutely check all of this, but why would it run great in open loop cold start if the injectors were an issue. The knock sensor I could see how it would be ignored in open loop and then seen in closed loop.

Mine was doing things very similar to what you are talking about.

Not saying the injectors are the issue, the clips could be broken and could be moving/reducing contact.

Have you cleaned the injectors?

Check the O2 sensors and make sure you have them in the right banks.

Check resistance of the O2 sensors as well, FSM calls for 5.5-6 OHMs.

 

[tmxmotorsports]

Check your battery connections and grounds

 

[CharlieS]

I haven't cleaned the injectors. Maybe penny wise and pound foolish, but it was running well before I did all of this work, so I (possibly incorrectly) figured it was good enough.

I will try to physically manipulate and check each of the injector clips.

I'll also review the fsm resistance tests for the o2 sensors, and check them with my multimeter.

I checked my grounds and battery connections earlier this evening but will triple check all of them.

 

[BILT4ME]

Also check the wiring connection on both temp sensors. One is for the computer, one is for the gauge.

If it does it when warm, then it could be triggered by the temp sensor.

Also look at IAC valve since it's affected when warm.

 

[ceylonfj40nut]

Is your accelerator cable installed per FSM? Have you checked your intake tube to see if it is on snug and not cracked anywhere? Sometimes you have to take it out and twist it a bit to confirm no cracks.

 

[CharlieS]

Intake tube is a brand new genuine Toyota part. The ends are seated and the clamps are tight.

I'll have to look up the accelerator cable adjustment in the FSM. I just put it back where I thought it was when I undid it.

 

[Desert Dino]

I have the same issue after resting the ECM

It takes time for it to learn itself, you should drive it tern off and restart

If you have Toyocom look what IAC is doing it should change slowly to the set point.

 

[CharlieS]

For future searchers, here is the cable adjustment procedure from the '94 FSM.

Except... my throttle cable doesn't have a stop.

 

[OffRoadScott]

As @BILT4ME mentioned earlier definately check the coolant temp sensors. As he did mention there are 2 different sensor, one for the gauge and the one the ECU reads. While your are in there might as well replace both.

 

[ajax1]

If you disconnected the battery or reset this will happen, I would give it a minute before you start chasing things

 

[CharlieS]

Thanks all. Working through the checklist you all provided (around the edges of my work day). I messed with the accelerator cable a bit and adjusted it to the ballpark of 650 +/- 50 in neutral after warming up and it is a bit happier idling there. Still not smooth, but at least not trying to stall. I don't like that I did this, and am treating this as a diagnostic tool to keep it running so I can continue to test. I don't feel
like this could really be the way to adjust idle rpms. That adjustment is fiddly - just tightening the jam nut alters the setting if I'm not careful.

Coolant temp sensors are plugged in and undamaged. I need to test them with the meter.

I still need to test the IAC, but need to research it first.

I like the idea of just driving it, but at the moment the alignment is so bad (new tie/relay rods and ends) that it is borderline scary. I could mess with driveway aligning it, but I have an alignment appointment on Friday, and want to get it running smoothly enough to get it there and back.

All grounds look right.

Battery terminals and connections are all snug.

I don't have Toyocom, but will look into it.

 

[LTSR]

Checking vacuum is one of the easy things you can check for. I typically just use some brake cleaner and go from there. I know you messed with a few vacuum related parts.