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Discussion Starter · #1 · (Edited)
Hi specialists. I was driving my car to an event where we stayed for a couple of hours, car was not running. No problems so far. When we left the event, I noticed the CEL was on and the car was running poorly. It seemed to run very rich, did not respond to the pedal very well. Immediately tried to read the codes with shorting the connector but it did not work.

Drove (as well as I could) the car back to my garage and tried again to read the codes, still no success.

Replacing the plugs was the first, easy choice - not helping. Checked the distributor, it was rusty but cleaning did not change anything.

I noticed the cam towers were leaking oil so I took the engine into pieces, replaced the seals and thought I might also take the injectors to a shop while everything is now taken apart. Injector maintenance was completed and the engine was put back together. It runs better (3 injectors were leaking and output was bad in 2 units) now, but idle still changes between 500-1000rpm all the time. Also, CEL is still on.

I thought perhaps the wiring is a problem in the connector so I shorted the pins in the ECU connector to be able to read the codes - still nothing. CEL just stays on and will not blink.

Someone proposed to use the old, analog type of reading codes, but there is supposed to be 3 diagnostic connectors and my car only has 2 so that also does not work.

Next task was to start doing the diagnostics according to the manual I found online in the group Facebook page. That manual seems to be for a newer model since my car has the older model of TPS and there is no Idle Speed Controller as stated in the manual. So I tried measuring resistances and voltages from the ECU connector but this is not working since the values are for newer model. Of course some of those work, for example ECU seems to have power and grounding properly. Most of the wires are the same as in the manual anyway.

This has taken weeks now and I just cannot figure out what could be causing this. Any help is much appreciated. Thank you for taking some time to read my long post.
  • What can possibly make the idle go up and down like this?
  • What will make the CEL stay on no matter if I short the diagnostics connector? Grounding?
  • What devices will be checked when the ECU diagnoses the system? Temp sensors and TPS, of course but what else? Signal from the distributor when cranking? Anything else I should check?
  • Is there a repair manual somewhere online for the older model?
edit: MA61, 5M-GE, 1984/1985 Euro-spec
 

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I started to make a wager what it was, but noting you're from Finland and some mention of not having an iacv, maybe we better understand which year model and which engine you have before we start guessing.
 
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Discussion Starter · #3 · (Edited)
I started to make a wager what it was, but noting you're from Finland and some mention of not having an iacv, maybe we better understand which year model and which engine you have before we start guessing.
Uh, stupid me. I thought I had the car info in my signature but apparently not. Sorry about that, added it to the end of my post. MA61, 5M-GE, car is probably 1984 but registered 1985.
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Hmmmm..... For a 1984, your market must have gotten some setup unlike what we got here in the US. I'm looking for an ISCV in the picture and all I see is a dark, apparently unoccupied space. But my guess is your throttle position sensor. I would test that first. I've seen it before where the idle speed goes up and down and up and down when the tps is unable to register the closed throttle position. Its like the computer is still doing its thing, trying to regulate the emissions, fuel mixture, timing and such in closed loop as if you were driving down the road. It doesn't know that you intended for it to go into open loop (which you told it to do by taking your foot off the gas) and lock everything into a static idle setting.
 

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Discussion Starter · #6 ·
I'm looking for an ISCV in the picture and all I see is a dark, apparently unoccupied space.
Yes, I was wondering the same.

But my guess is your throttle position sensor. I would test that first.
It has been tested and I even shorted the pins to make sure ECU gets the "throttle closed" signal. Not helping.

vacuum leak.
Between AFM and intake valves

does this car have O2-sensor?
Vacuum leaks are possible but I tried searching for them by spraying brake cleaner all over the hoses. Nothing.

And no O2 sensor in this car. We did not have unleaded fuel that time so no catalyzer.
 

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Discussion Starter · #7 ·
One additional question; how common is a failure in ECU in these cars? I mean, they are 40 years old anyway so components inside are very old and subject to failure. There are good instructions for the MR2 (SW20) ECU repair, wondering if there's something similar for Celica Supra?

After all, the first sentence of the article says:
"Has your MR2 been idling rough or unevenly? Is it hard to start first thing in the morning? When you come to a stop does the idle dip down a little too far and then come back up? "
 

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With regards to the Check Engine codes, it is possible that the European 5MGE engines used an EFI system similar to the 1982 North American system which did not have a Check Engine Function.
Does your distributor have a vacuum advance diaphragm? If it does, that would indicate that your car does not have TCCS.
The Toyota Computer Controlled System was an EFI controller that electronically controlled the ignition advance. This was introduced in 1983 in North America and used an analog meter to display error codes. In late 1984/1985 the error codes were indicated by the Check Engine light flashing.
The Igniter in your picture is similar to that of the North American market 1982 Igniter, so I wonder if this is why you cannot see error codes....there are none.

North American 1982 owners may be able to help with troubleshooting if this is the case. Especially if they have a 1982 Service manual set.

Dale
 
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Maybe it has the IAC valve that was in the 82 US model.
Could be, as we see a hose from the overpass tube going towards the intake plenum (about 25mm dia) That could very well be the idle valve, which is simply controlled by 12V applyed to it, iirc.
 

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Discussion Starter · #11 ·
Could be, as we see a hose from the overpass tube going towards the intake plenum (about 25mm dia) That could very well be the idle valve, which is simply controlled by 12V applyed to it, iirc.
I don't see any wires going there. The only wiring is for the TPS.

If you guys think there is no diagnostics system, why is there a CEL anyway - and it's on? Definitely there seems to be something wrong and the ECU identifies it since the car seems to run very rich at the moment.

If I hit the gas very fast, the engine almost dies but if I press the pedal slowly, the engine revs up.
 

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Discussion Starter · #12 ·
Added a couple of photos just to help you see what is there in my engine bay.
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I'm just trying to see how your idle speed control works. European cars seem to be slightly different from USDM vehicles in how they are equipped. As a result, I would imagine that the troubleshooting will be somewhat different.

1982 USDM cars I assume have a check engine light, but did not store check engine codes. It would light when things like the alternator regulator charging stopped working. It was a much simpler system. I really do not know if the European cars stored error codes or not.

From you latest pictures, you definitely do NOT have a vacuum advance distributor, so it does not quite compare to the 1982 USDM cars. I would imagine then that you do have the TCCS EFI/Ignition control then. However, it looks like you do have the IAC (Idle Air Control) valve of the USDM 1982. This is a simple on/off solenoid valve that bypasses the throttle blade of the throttle body to let the motor speed up slightly when things like air conditioning turn on at idle to prevent the motor from stalling.

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IAC Valve

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IAC Valve plumbing on a USDM 1982. 22230A Hose leads to the air intake over the cam covers.22230B leads from the IAC Valve to the Intake manifold.

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1984 USDM ISC Valve

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USDM ISC VAlve close-up

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1983 and up. Item 22270 is the ISC valve. Item 22270A leads to the air intake over the cam covers. The ISC bolts onto the front left side of the intake manifold.




By comparison, the 1983 and up USDM cars have an ISC (Idle Speed Control) valve which can step 255 discrete steps to fine tune the idle speed. The concept is the same, at idle, the valve bypasses the closed throttle blade in the throttle body to speed up or slow down the motor idle speed. As a result, the idle speed can be controlled more accurately.

Does your car have a catalytic converter? I'm just curious, because the USDM cars do, and the TCCS has errors for an Oxygen sensor. I would imagine this could affect how the system works.







Back to the original issue though, as Dannoxyz said, it sounds to me like there is an air leak between the air flow sensor and the intake. When this happens, it does not correctly match the amount of fuel being metered relative to the air flow. I would have thought that it would have run lean rather than rich, however.

Smooth idle, no throttle response

As EastClintwood found, an air leak can cause symptoms somewhat like what you describe. Idle is okay, but when applying throttle, the engine loses power and stutters. His car was a 5ME, not a 5MGE, but the concept is the same.

Unfortunately, his post no longer has the photos, but it was a leaky air hose on the intake.

Hopefully this is something simple like he found.

Dale
 
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Discussion Starter · #14 ·
Hopefully this is something simple like he found.
Hi Dale

Thank you very much for your informative post. However, as I said in my first post, the idle is not stable but it varies regularly between 500-1000 rpm (approx.) all the time. Also, this started when the engine was off and I realized the issue when we next time started driving.

Also, if there was a leaking hose letting too much air in, I also thought the engine would run lean, not rich. I also don't think that would lit the CEL.

Uh, you also asked about catalytic converter. The answer is no. We did not have unleaded fuel that time so we did not have those that early. I believe only in the mid 90's those became mandatory.
 

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FinToy, seems like the leaky hose may be the issue.
 

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Vacuum leaks are possible but I tried searching for them by spraying brake cleaner all over the hoses. Nothing.
That's not 100% test for leaks because if you have large leak or more than one, it's not possible to cover them all with brake-cleaner or propane simultaneously. Try this pressurised test: A Good-ish Car with a Good-ish Owner: A Quest to get my... Also squirt underneath intake-hoses, they like to split underneath hose-clamps on lower side where you can't see them.

Also as test, disconnect electrical connector from ISCV. Usually the idle-speed cycling is due to ECM trying to play catch-up with leaks, resulting in sine-wave.
 

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There is a second device that controls throttle bypass airflow as well. Possibly, it could be in this area.

If I recall correctly, it's the power steering pump system. When power steering is working hard, it can slow the motor down so there is a separate bypass circuit. If either the power steering pump or the lines leading to and from it are leaking, you could get similar issues.

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Sorry for the wiggly line. Too much coffee.

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These lines go down to the power steering pump and are ported.

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Lines to and from the power steering pump switch.
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Where the lines go down to and up from the power steering pump.

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Where the line from the power steering switch enters the intake manifold (the right or index finger).

This may have nothing to do with it, but my grandson had a Cressida that wouldn't idle because this circuit had a cracked hose. I had no idea what this stuff was before trying to help him.
Just be aware that you should leak check these lines too!

Dale
 

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Is the TB dirty? clean the TB butterfly plate.

Disconnect the TPS, go for a test drive, note any changes and report back.

Make sure no one has messed with the idle air adjustment screws on the TB.

Will

edit 2222 post!
 

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Discussion Starter · #19 ·
Try this pressurised test: A Good-ish Car with a Good-ish Owner: A Quest to get my... Also squirt underneath intake-hoses, they like to split underneath hose-clamps on lower side where you can't see them.
This seems to be a good tip, thanks.

Also as test, disconnect electrical connector from ISCV.
The problem is that my car does not have ISCV.

Is the TB dirty?
No, it's all perfectly clean.

Disconnect the TPS, go for a test drive, note any changes and report back.
If I disconnect the TPS, the car will not be able to drive?

Make sure no one has messed with the idle air adjustment screws on the TB.
As the problem started in the middle of the drive, I doubt this would be the cause.

Guys, I really appreciate the efforts and I know how difficult it is to say something without even seeing the car. Thank you.

So, I'll check the vacuum leaks again and report back.
 

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In our markets, the idle device is at the end of this tube. Might be the case at your location too. As for the TPS, does not hurt to try disconnected.
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