An interesting high idle issue (1 Viewer)

[Spook50]

Since my injector swap and installation of the bored out throttle body, I've been methodically troubleshooting a high idle. After ensuring that the throttle plate is indeed closing properly, dashpot is backed off completely (will be adjusted to factory setting once idle is corrected) and TPS is properly adjusted, I checked the AFM. Everything there checked fine, save for continuity between E1 and FC in the "other than open" position. Instead of a being zeroed out it reads 1.1Ω, which I honestly don't think is important, given this is basically a switch that, when open, causes power to the fuel pump to be cut.

My next step was to check the ICS. I pulled the motor off of the base plate so that I wouldn't have to pull the coolant lines connected to it. While off I inspected the O-ring on the base plate and it was still in good condition. I then bench tested the motor following the procedure in the FSM. It checked out perfectly for both the ohm check and the function check. I gave it a quick clean, lubricated the shaft in the motor, inspected inside the base plate for any obstructions that might prevent it from closing, and reinstalled the motor. Cleaned the electrical contacts and plugged it back in. Drove it around for a couple days and the warm idle was rock steady at 650 RPM. Today the warm idle wouldn't go below 1000 RPM. I'm being led now to believe that either the ECU is getting a faulty signal from something (possibly the engine temperature sensor, of which I have a spare OEM unit); or just as likely, a faulty connection either in the connector or an old wire running along the engine is failing. Another possibility that I high doubt is the culprit could be a failing ECU. Possible, but doubtful.

So my next step will be to ohm out the connections on the harness and the ECU associated with the ICS. If those look good I'll inspect the temp sensor.

Step by step here, but thought I'd add to the mountain of high idle threads with my methods of troubleshooting for the benefit of anyone in the future who finds themselves chasing an idle issue.

 

[Michael Hanson]

Hi, I think you knocked something loose when you did the work. Check all wiring for looseness or small broke or corroded wires.

 

[Godwin]

Or a sticking throttle cable because it's >30 years old.

 

[Spook50]

Checked both of those and all good (save of course for the ICS circuit, which I'll be shooting with the multimeter at the first chance I get to see if it's actually good or not. @Michael Hanson your thought is the direction I'm going at this point, since the idle did sit right where it needed to for a couple days after I fiddled with the ICS).

I've gotten into the habit of lubricating the throttle cable every couple of years, though to be fair I could probably stand to replace it entirely at this point for the sake of preventative maintenance.

 

[Spook50]

Well damn. ICS circuit and the engine temp sensor circuits (and the sensor itself) are both good.

It's as if the ICS isn't closing far enough to bring the idle back down below 850 RPM. Whether it be the ECU thinking that 850 RPM is right, or the ICS just not moving past that point. I'm leaning towards the ECU not closing the ICS enough (whether from some faulty signal or the ECU itself failing, though I still doubt this is the problem because I would expect other issues to occur as well if that were the case), or the ICS itself just not functioning properly, despite passing a bench check and being able to cycle all the way to the closed position manually on the bench. I do have a spare ICS motor that I'll test, and if it's good I'll clean and lubricate it then swap it in.

If that doesn't do it, it'll be time for another study session with the FSM.

 

[toy_tek]

I know you said you checked the TPS measurements, but does it snap fully back closed on it's own? Perhaps it's hanging up.

 

[Spook50]

I know you said you checked the TPS measurements, but does it snap fully back closed on it's own? Perhaps it's hanging up.

Yep that was one of the first things I checked before checking to make sure the stop screw was letting the plate close entirely (both of which checked out just fine). The adjustment screw has a fresh O-ring, seals properly and and is adjusted all the way in. My stock throttle body had the screw only out 1/16 or so of a turn.

I went ahead and replaced the ICS with my spare last night and drove it a couple times since then with the same results. Everything else behaves like it should. Engine runs smooth and strong, vacuum is steady so no indication of a leak, cold startup idle is 1200 RPM like normal, but once hot it will only settle down to 850 RPM. I've eliminated the ICS now as far as the possibility of an electrical fault or physically jamming, tested the water temp sensor (hot and cold) and the cold start injector time switch, both of which were good. Ensured both had good solid connections and signals are reaching the ECU.

I'm not 100% certain, but I'm leaning more and more towards the ECU is simply not setting the ICS down far enough to bring the idle to 650. Something else that pushes me in that direction is when I bench tested my original ICS, I reinstalled it with the plunger almost completely closed. Startup and run for a short while after that had WAY low idle that eventually "corrected" back to the high idle I'm experiencing now.

This weekend I'm thinking I'll pull the ECU entirely and do all the checks I can on the bench that the FSM details, in hopes of eliminating the ECU itself from the list of potential culprits.

Kind of humorous that I get the infamous 3FE high idle after a big job, and it's not one of the simple issues or a bonehead mistake I could've made when putting everything back together

Edit: I'm going to give it a little more time before disconnecting any electrical and see if I can get a code to come up in diagnostic mode. Before I get any more in depth with electrical troubleshooting and now that I've eliminated the obvious mechanical possibilities, I want to see if the ECU will throw any codes.

 

[toy_tek]

Any chance the AirCon circuit is telling the ECU to high idle all the time? Can you tell if it's cycling?

 

[Spook50]

Any chance the AirCon circuit is telling the ECU to high idle all the time? Can you tell if it's cycling?

Interesting thought. I kind of doubt that's the case but wouldn't hurt to check and be sure. I'm putting the 62 back together from finally pulling my transmission temp gauge out (leftover from the A440F but not really necessary with the H55F) so I'll give it a looksee when I fire it up.

Before disconnecting the battery to remove the gauge I checked for any codes with the ECU, and unfortunately no codes that could give me a hint.

 

[Spook50]

Welp, definitely not the AC idle up circuit. I've pretty much eliminated anything electrical, verified the O2 sensors and temperature sensors are still good, TPS and AFM are good and TPS is properly set. Have two known good ICS motors, both clean and lubricated, clean ICS base plate.

Idle isn't WAY high (850-900), so it's not a critical issue, but given my obsession over making sure my engine is running at factory spec, I'm going to keep troubleshooting. Next step will be spraying some starter fluid around the intake manifold and seeing if there's a leak somewhere. I doubt it, given vacuum holds totally steady at both hot and cold idle, but I want to be absolutely sure.

If that doesn't give me any answers, I'll be setting my timing back to factory spec so I can start at a base line. The only reason it's still advanced is because it idled perfectly at 650 before I did the manifold/throttle/injector job while set at 12º TDC.

 

[fjc-man]

Isn’t there a ground cable that sometimes is loose at its attachment to the intake manifold?

 

[Spook50]

Isn’t there a ground cable that sometimes is loose at its attachment to the intake manifold?

There is a bonding cable, yes. It attaches between the #4 and #5 intake runners. It wouldn't serve as a direct ground per se, but more of an electrical bond between the aluminum upper intake, magnesium lower intake, and the iron and steel that makes up the rest of the vehicle, with the end result/goal being prevention of bimetallic corrosion.

I could be wrong, given I haven't completely disassembled the engine wiring harness, but I don't believe any electrical components rely on that as their sole grounding point. Regardless, mine is connected, with some carbon conductive grease that I use in most permanent electrical connections.

 

[RevISK]

This may be stupid but have you tried pulling up on your gas pedal to be sure it’s not sticking?
That was happening on my 62 so…

 

[toy_tek]

This may be stupid but have you tried pulling up on your gas pedal to be sure it’s not sticking?
That was happening on my 62 so…

Not stupid. Once my hand throttle cable was not slacking when pushed fully in and caused a high idle.

 

[RoaringFork]

Take this with a grain of salt as I am no 3FE expert…

Has any re-mapping been done to the ECM for the larger throttle body?
To my knowledge, with an EFI system, the diameter of the throttle valve is part of the air mass calculation. IE, 5grams per second through a 70mm bore is less air than 5grams per second on a 90mm bore.

With a smaller bore the same amount of air moving past the VAF will have more velocity(more movement of the VAF, higher reading to the ECM) than with the larger bore. Possibly in your situation the VAF is reading lower with the large bore(less velocity) and the ECM is “seeing” a lower air mass value and bringing up the idle to increase the VAF reading.

If you swap the old throttle body in and all is well, I suspect this may be the issue. HTH

 

[Spook50]

This may be stupid but have you tried pulling up on your gas pedal to be sure it’s not sticking?
That was happening on my 62 so…

Definitely not stupid, as it's becoming a more common problem with FJ62s given the length and wear on the throttle cables. I do lubricate mine every couple years using a tool for lubricating motorcycle cables, and just to be sure, I checked the cable and throttle valve when this started. No stickiness here at this point in either spot.

@RoaringFork you may very well be correct. Swapping on the old throttle body is, at this point, a "last resort" given the need for pulling off two little coolant lines, and the fact that my only gasket is the one that's currently in place. It's not uncommon in the 22RE world for those with larger throttle bodies to adjust the AFM, which I didn't want to cut open and be arbitrarily screwing with, given how easy it could be to seriously mess things up with one wrong move. The only thing that didn't have me considering the larger throttle body right away is that this is the idle with throttle fully closed; in which case the idle speed is solely adjusted by the ICS (Idle control Solenoid). Everything above fully closed throttle is right where it should be.

Something I also did was completely strip down, clean and rebuild a spare upper intake manifold, so there's a lot of potential leak points that I'm going to double check with some starter fluid hopefully this afternoon and see if I can find any spots that'll make the engine accelerate. I was sure to use high temp thread sealant on each fitting, but my ego isn't so fragile that I refuse to consider the possibility of screwing up one or two

 

[Spook50]

Both the starter fluid trick and the smoke trick indicated zero vacuum leaks. I blew smoke into it until it was wafting out of the air intake itself

Hopefully Thursday I'll double check the TPS to see if maybe I tweaked/nudged it while securing the screws, then do the O2 sensor test outlined in the FSM to make sure they're operating correctly. I'm pretty sure they're over ten years old (at least) so I'll be surprised if they're spot-on, but hopefully will still be within spec since the ECU didn't give me any codes at all.

If all that's good, I'll do a test on the O2 sensor reading itself on one of the sensors that was outlined in another thread by an old BMW tech familiar with Bosch systems (which the 62's is almost a carbon copy of). This will tell me if the ECU is actually holding an ideal air-fuel ratio under an above-idle no load condition.

 

[YooperCruiser]

Disconnect the battery and let the ecu reset

 

[toy_tek]

Edit .. already covered

 

[Spook50]

Disconnect the battery and let the ecu reset

That was among the first things I tried. No change on there.

I'm hoping I can find something out tomorrow afternoon when I'm hoping to check the O2 sensors and then make sure the A:F mixture is correct. My hope is that if it IS out of whack, it could be tied to the same thing that's causing the ECU to just hold it at 850 RPM.

On the plus side, it's not so horribly high that it's making it undriveable, but it's enough to tell me something is not quite right and lead me on a chase to find it.