1990 v6 automatic troubleshooting

[4RunnerAuto]

Hey folks,

this forum has proven to be an invaluable resource for all nature of repairs on a 1990 3vZ automatic transmission, so thanks to all the contributors here! 1990, 214k miles, automatic transmission, pretty much all original...

I know this is a long post, so whoever chimes in I really appreciate it! I have provided (maybe too much) detail in the post to help eliminate possible causes so that I don't go down the wrong rabbit hole. Or at least, hopefully, I'll reduce the number of rabbit holes I must enter.
I have searched the forums/threads here thoroughly regarding my questions/issues in this post, so if there are existing links that diagnose the same issue I apologize for adding to the confusion, and links are appreciated!

Chasing issue of rough idle:
Somewhat recently I started noticing a rough idle. I don't want to muddy the waters here, but I am pretty convinced I did not notice this rough idle until after I removed the belt to the A/C compressor. (I disconnected compressor due to bad clutch, which rattled for a few days before I could pinpoint the source. I searched at the time for posts about replacing the A/C clutch, it seemed like it was difficult/problematic to do with compressor on the engine, so I pulled the belt).

Enter the rough idle. At first, when I noticed it (at a traffic light) I would shift the transmission from D to P or N. The engine would smooth out in P or N, and when I shifted back to D it would become rough again, but never stall. At this point I started considering possible issues with idle related to lack of A/C belt.

As the weather has gotten hot, the rough idle has worsened, and now the engine actually stalls when it is hot and idling. I can pretty much count on it to stall if I have driven the car for an extended length of time, especially if I turn the car off and then restart. (Example: drive long distance, engine hot, beerrun, driving home the engine stalls leaving the parking lot, and at stop lights to home). Hotter temperatures seem to make the issue worse. No apparent issues when the engine is cold or warming up. The engine currently stalls (when hot) with the transmission shifted in to all positions, with none being smoother than the other. If the engine is hot, and it is hot outside, it stalls a lot. If the engine is hot, and it is not-so-hot outside, the engine stalls less or not at all. If I drive it for a long distance and never shut the engine off in the middle of my commute, it can get me home without stalling but the idle is VERY rough at stop lights, and I often shift to N and give a little gas to keep it smooth and running. The factory tachometer in the dashboard seems to hover at or below 500 RPM with engine hot and idling in D.

1990, 214k miles, pretty much all original... original motor and transmission, 3 head gasket replacements to date, fuel pump replaced ~10 years ago. Transmission cooler installed, so no coolant reservoir. Fluids checked regularly, and there is no abnormal consumption of oil or coolant. Slight pwr steering leak.

Side note: after last head gasket replacement in 2006, the check engine light remained on until 1 month ago; I replaced the spark plugs (rough idle...) and the check engine light has disappeared. Weird.

New Air filter with new spark plugs 1 month ago, no difference in idle issues. The car was relatively underutilized for a little while, and when I changed the air filter I found significant debris in the cleaner housing which made me hopeful that the clean filter would help the issue.

Any and all input is appreciated, thanks again for a great resource!

 

[Eugene13]

Im no expert on these motors or transmissions by any means, just trying to help, but to me it sounds like a wiring issue or similar. Maybe a sensor or some sort of solenoid somewhere? MAF? Not sure but it sounds like whatever is telling the engine to idle in D, N, or R seems to be getting a faulty reading. Just my .02 :shrug:

 

[old87yota]

It could be several things.

Off the top of my head, this sounds like a vacuum leak, but...

First, have you checked if there are any stored codes in the Engine Control Unit?

The "Check Engine" light has been on for quite some time. Does the "Check Engine" light come on when the key is turned ON Position (engine not running)? If not, the bulb may be burned out.

There could still be stored codes even if the "Check Engine" or Malfunction Indicator Lamp is no longer on (assuming the lamp still works).

Here is how to check for codes and what the codes mean: http://www.teamtoyota4x4.org/archivio/1990-1995_4runner_wm/techinfo.toyota.com/ileaf/95toyrm/95toypdf/95rmsour/1995/954runne/eg2/mfisyste/diagnosi.pdf

You can use a paper clip in place of the SST 09843–18020 to jump the TE1 and E1 terminals.

Knowing what codes are stored gives you a window into what the Engine Control Unit is seeing.

:fro:

 

[4RunnerAuto]

Still figuring

Eugene13 and old87yota, thanks guys for your thoughtful replies. My apologies in letting the thread go quiet so soon, I've been otherwise occupied.

eugene13, I have indeed wondered about some sensor (MAF/02 or something) and was hoping to get some insight on that. I'm going to dig around more in this forum and others.
old87yota, I have also considered vacuum leak as the culprit but haven't actually been able to locate or hear anything that I can pinpoint. after I replaced the spark plugs, I started hearing a lot more of what has been described as "lifter noise," but regardless the idle issues preceded this lifter noise. I have not checked for stored codes in the ECU. After the mechanic did the head gasket and the light remained on, he claimed that they couldn't get the light to turn off, and that for the light to turn off the whole ECU would need to be replaced because the car is old. I am skeptical on this information. The check engine light does come on when the key is turned to ON, so the bulb is not burned but I had the same thought! I am going to refer to the engine codes thread and see what I might glean from there. Even though the light has gone out, there might still be a code to read?

Anyhow, the idle problem persists as described. It definitely seems temperature related. It definitely is worse if the engine is hot, has been shut off, and restarted while still hot. There is a slight, but perceptible difference if I have the transmission in P,N, or D/R. The car tends to die more in the D/R positions.

Thanks again!

 

[4RunnerAuto]

Hey guys, update here: A while back I removed all parts of the air intake to check them out. I did find a large crack in some of the "flexible" tubing, directly where it squeezes on to the throttle body. I patched this up with some gasket maker and clamped it back on there. I am assuming I have a tight seal here now, and I saw no other fail points (but the tubing is original from 1990). While I had the intake assembly off, I used some throttle body cleaner and sprayed around the inside of the throttle body, especially on the idle air control valve/bypass valve IAC in front of the air intake port/choke. I did not remove the throttle body, so I didn't spray tons of the stuff to avoid potential issues there. For a brief few minutes I thought I might have found a solution, but no such luck, idle problem as usual. After a couple more days, the check engine light came back on, so I finally got around to checking the engine code. I jumped the terminals with a paperclip, following the instructions to the link from old87yota. (Thanks!)

It is throwing code 25, "air-fuel ratio lean malfunction" with the following troubleshooting guidance:
•Engine ground bolt loose
•Open in E1 circuit
•Open in injector circuit
•Fuel line pressure (injector block-
age, etc.)
•Open or short in heated oxygen
sensor circuit
•Heated oxygen sensor
•Ignition system
•Engine coolant temp. sensor
•Volume air flow meter (Air intake)
•ECM

Is there good reason for me to suspect or replace one of the various sensors over the other? Above guidance mentions volume air flow meter (MAF?) and oxygen sensor, any other possibilities like TPS?

Thanks again everybody.

 

[RedDawn]

This sounds like my rig I just bought, less the check engine light!!! How strange!

Did you ever figure out what was the cause? In addition to the rough idle when hot, and stalling, i'm having an overheating issue with my transmission as the truck is basically stock. IF you can point me in the direction of trans cooler i'd appreciate it!

 

[DustyDog]

Hi new to the site.
I have a 1990 3.0 VZE with an idle problem as well. I am throwing code 25, have replaced o2 sensor but light comes on a few days after I clear it (a couple of times now).
I had a surging idle problem that seemed to get worse on cooler days, when I first start the truck the idle is way high - like 2k rpm - then after warming up will cycle from about 1k to 2k every few seconds. I looked it up and there are some coolant lines that run through the throttle body to what is the IAC control valve (I assume that is what I am looking at, almost like a little thermostat looking thing with a spring under a cover on the side of the throttle body). Sure enough one of coolant lines was completely blocked, so I changed it out for a new one and it ran pretty good for a few days. Then it was back to the same problem (high idle, surging idle). So today I checked it out again, no blockages as far as I can tell. I did take apart that IAC valve from the throttle body, I'm not sure if what I did was correct but I took it out, cleaned it (there was some carbon deposits on the valve) and tightened the cylinder piece that holds the valve in pretty tight - the valve before was almost flopping around in it's housing. I started the truck up, idle was about 1100 rpm. Drove it around, seemed okay. Got home, put it in park and the idle immediately shot to about 2k.
So I'm a little lost, what I originally did (replace coolant line coming off the throttle body) seemed to really help but it went back to the same issue after about a week.
Any suggestions or anyone had any look trying anything else for this issue?

 

[Rnc1592]

Same rough idle issues with my 93. I'll be following this! I think mine is a fuel injector issue, but I'm not 100% as I haven't had a chance to run codes yet.