Rough idle - my fault, but I don't know what I did (1 Viewer)

[CharlieS]

Checked vaccum with brake cleaner. Idle definitely picks up temporarily when I spray under/around throttle cam/cable, or under it. I don't see any uncapped lines, but will look closer after work today. Wonder if I did some bonehead move like under-torquing the plenum fasteners leaving a crack that unmetered air gets into... There were not any other areas in the engine bay where the idle changed with application of brake cleaner spray. This is very helpful.

 

[Malleus]

@CharlieS Nothing you did would affect the idle, IME. The ECM doesn't have any learning function related to idle.

The symptoms point to the IAC. There are two tests, one which can be performed without removing the IAC, one which cannot. Pulling the throttle body has always been required for me to remove the lower of the two mounting screws (I replace them because I didn't trust that I'd be able to tighten them after mangling them to get them out).

I went through this with my '94 a few months ago. The solution was to remove, disassemble, clean, reassemble and reinstall the IAC. It works flawlessly now. Some have gone through this exercise and still not had a working IAC. The '93-'94 IACs are NLA, but the later '95-'97 IACs are still available and are direct replacements, if you need a replacement and want a new part ($$$). There is a small amount of tribal wisdom that indicates the early parts die early, but the late ones appear to be OK. My '94 is a NOV model and my DD '95 is a JAN model, so they're pretty good side-by-side comparisons. My '95 has no trouble at all.

My '94 didn't have a stop on the cable either (that was my first troubleshooting step). Bummer.

 

[CharlieS]

I'll dig into this tonight. Thank you.

 

[CharlieS]

Also, not sure if I mentioned this, but I DID use new Toyota intake and plenum gaskets.

 

[Shipwreck]

I agree that idle issue points to the IAC. If you have adjusted your throttle cable tension to achieve 650 rpm idle, that is not right. Idle speed should be controlled by the ECM and IAC.
However, I would check the basics first. Spark, fuel and air/vacuum. With all of the modifications you did to the vacuum system, I would want to measure that vacuum is in spec. (Not just listen or check for leaks).
I would also confirm that your distributor was reinstalled without being off by a tooth. If your distributor is adjusted at the far end of its adjustment range to get to your 3 deg BTDC, that is an indicator that you might be off.

 

[cruiserdan]

How many start cycles since the battery was reconnected?

 

[CharlieS]

I agree that idle issue points to the IAC. If you have adjusted your throttle cable tension to achieve 650 rpm idle, that is not right. Idle speed should be controlled by the ECM and IAC.
However, I would check the basics first. Spark, fuel and air/vacuum. With all of the modifications you did to the vacuum system, I would want to measure that vacuum is in spec. (Not just listen or check for leaks).
I would also confirm that your distributor was reinstalled without being off by a tooth. If your distributor is adjusted at the far end of its adjustment range to get to your 3 deg BTDC, that is an indicator that you might be off.

Thank you.

That makes more sense to me, and I'll dig into IAC troubleshooting after work tonight.

Vacuum leak remains a leading candidate after the brake cleaner test I did this morning after a helpful suggestion above. I need to dig into the FSM.

I installed the distributor with the valve cover off, after aligning the rotor with the notch in the gear, and having the engine at TDC on cylinder #1, crank pulley aligned with the 0 on the block casting. Timing was about 0 before i made a very tiny adjustment of the distributor clocking to get it to 3 degrees BTDC. I am pretty confident that it is good.

I'd add that I cleaned the heck out of all of the ports in the intake and plenum with B-12 Chemtool Professional (good stuff!) and brake cleaner. I hope I didn't flush crud into the IAC and gum it up. I didn't take the IAC or the other one off because I didn't want to take them out of adjustment (at least one of those has a range of motion in the install screws).

Also I only have one 3.5 mm vacuum line coming off the head now (plus the PCV, vent hose and brake booster hose) - I updated to the single later gas filter with one pipe - it goes direct to the fuel pressure regulator now. No change in engine behavior with this disconnected, open, plugged, or connected. I can feel suction with my thumb, but haven't tested how much vaccum is being created.

 

[CharlieS]

How many start cycles since the battery was reconnected?

A dozen or so. I haven't been counting, but at least that many.

I drove it about a half mile too, but there is so much toe, I didn't want to keep going without making it more drivable. I set them to the FSM baseline specs but that gave it a lot of toe out. I might tweak it a little just to get me to my alignment appointment.

 

[leonard_nemoy]

@CharlieS do what @ceylonfj40nut suggests. Check your intake boot for cracks and make sure it is seated correctly and tight. Did you do anything to the airflow sensor?

 

[cruiserdan]

A dozen or so. I haven't been counting, but at least that many.

I drove it about a half mile too, but there is so much toe, I didn't want to keep going without making it more drivable. I set them to the FSM baseline specs but that gave it a lot of toe out. I might tweak it a little just to get me to my alignment appointment.

The 93-94 ECM needs to go through several start cycles, after a battery disconnect, for the IAC to re-learn the hot curb idle. Has the idle come up at all in the process?

 

[CharlieS]

@CharlieS do what @ceylonfj40nut suggests. Check your intake boot for cracks and make sure it is seated correctly and tight. Did you do anything to the airflow sensor?

I will check the intake tube again. I checked it last night and again this morning. I will check again tonight after work. I'll remove and reinstall after checking the condition of the sealing surfaces.

By the way, the intake tube/boot is brand new, no cracks. It is a Toyota part and is very pliable. But I will visually inspect it just in case.

 

[CharlieS]

The 93-94 ECM needs to go through several start cycles, after a battery disconnect, for the IAC to re-learn the hot curb idle. Has the idle come up at all in the process?

That is helpful information. Thank you.

I have made the rookie mistake of changing too many things to keep good track of this. I think it may have gotten a little better, but it also still drops the idle and threatens to stall, or stalls if I let it keep going once warmed up.

 

[cruiserdan]

Have you disconnected the battery at any time during your diagnostic process?

 

[CharlieS]

Have you disconnected the battery at any time during your diagnostic process?

I have not, but I can if that is a good thing to do! Would you recommend it?

 

[cruiserdan]

I have not, but I can if that is a good thing to do! Would you recommend it?

I was asking because every time the battery is disconnected the ECM loses it's IAC settings and it needs to start over. If power has not been interrupted the idle should be re-trained by now.

Since the idle has not changed, that suggests a vacuum leak to me.

 

[leonard_nemoy]

I will check the intake tube again. I checked it last night and again this morning. I will check again tonight after work. I'll remove and reinstall after checking the condition of the sealing surfaces.

By the way, the intake tube/boot is brand new, no cracks. It is a Toyota part and is very pliable. But I will visually inspect it just in case.

Sounds like it is good to go

 

[leonard_nemoy]

Spray a can of something volatile like starting fluid around the engine. Sometimes you can hear a change in the idle when you introduce the aerosol into a vacuum leak. Just keep a fire extinguisher handy

 

[CharlieS]

IAC testing

pins reference* reading
s1-s3 10-30 32.8
b2-s2 10-30 22.0
b2-s4 10-30 22.2

*ohms at 20 deg C/68 deg F

It is like 85 F ambient, and the engine is warm, so I don't know if that first reading is within reason. It is out of spec at that temp.

I guess the next test will require removal (and I don't have a spare o-ring handy).

Removed inspected and reinstalled the intake hose and am confident that it has a good seal.

Gave the intake bolts a little snug.

Oh, and starting with the IAC unplugged- yee hah 3k rpm in a hurry...

 

[CharlieS]

Winner winner chicken dinner. IAC plunger doesn't move when tested to FSM spec.

Battery + to B1 and B2, sequentially grounding s1-s2-s3-s4-s1.

I can hear a solenoid trying to do something, but no movement.

Wierd that AC does make the idle jump significantly, leading to a false conclusion on my part.

 

[CharlieS]

Any IAC disassembly tips before I break it? I got the three small brass colored screws out (watch out, red loctite).

It doesn't want to come apart easily from here. I don't want to force it.