[Troubleshooting] High idle CO - MOT fail

[Laurens PNut]

1992 MR2 SW20
3SGE N/A
MT
215.000 miles

fresh spark plugs NGK BKR7
fresh engine oil
open air filter
Mongoose exhaust (de-cat)

I have failed MOT for the second time due to not passing the emission/smog test.
I must meet 3.5% CO max at idle but it is 4% and sometimes it shoots up even to higher values...

I don't experience abnormale fuel usage, the car comes up to temperature without issues, idle is not bouncy, at stable at 750 - 800 rpm.

Still, the car is running way to rich obviously. What could the issue be?

The non-branded garage said it can't be the oxygen sensor, those values were ok.

I made an appointment at Toyota but i'm still trying to figure things out.
So what have I done so far:

- the air intake temperature sensor was disconnected > reconnected
- reset the ECU
- visually check the ISCV > not cracked
- checked vacuum hoses > old but not cracked or anything
- jumped TE1 and E1 and noticed a CEL blinking which referred to a faulty TPS sensor afaik

Question:

- how to properly adjust the TPS on this car
- how to properly adjust the ignition timing
- idle speed screw on the throttle body is turned all the way in, is that normal?

I could understand that a combination of the things above can result into failing emission at idle even though the car is perfectly driveable.

In what order do I have to do the things above and how..?

[Peter Gidden]

To adjust TPS, bottom two contacts in TPS need to be closed (with ohmeter) when TPS is at rest. The contacts should open with 1-2mm of rotation of throttle plate.

Ignition timing should be set to 10 degrees BTDC at inormal idle with E1 and TE1 shorted.

[Laurens PNut]

About the TPS adjustment; I'm used to Nissan TPS sensors where you use your voltmeter to short 2 pins, get a readout (0.45v as the lowest and 5.0v as the highest and the you have to set it around 0.60v).

Is this procedure the same on the SW20 3SGE?

The way you describe it doesn't make it clear for me when TPS is set the right way. Do I have to see a certain readout? Because the turning radius after loosen up the top and bottom screw is quite big,

[Laurens PNut]

About the TPS adjustment; I'm used to Nissan TPS sensors where you use your voltmeter to short 2 pins, get a readout (0.45v as the lowest and 5.0v as the highest and the you have to set it around 0.60v).

Is this procedure the same on the SW20 3SGE?

The way you describe it doesn't make it clear for me when TPS is set the right way. Do I have to see a certain readout? Because the turning radius after loosen up the top and bottom screw is quite big,

I'm reading it again, maybe you mean I have to measure the pins and at the same time move the throttle cable to open up the butterfly valve?

[Peter Gidden]

Bottom two pins of TPS are a switch thatbtells the ECU when throttle is closed.

So you need to adjust TPS so the switch is closed when throttle is closed. And so the switch opens with 1-2mm of rotation of the throttle spindle.

[abovetherim]

About the TPS adjustment; I'm used to Nissan TPS sensors where you use your voltmeter to short 2 pins, get a readout (0.45v as the lowest and 5.0v as the highest and the you have to set it around 0.60v).

Is this procedure the same on the SW20 3SGE?

The way you describe it doesn't make it clear for me when TPS is set the right way. Do I have to see a certain readout? Because the turning radius after loosen up the top and bottom screw is quite big,

I used this on my 3sge

[Laurens PNut]

Brought the MR2 to the Toyota dealership and they did some testing.

oxygen sensor > OK
TPS sensor > OK
AIT sensor > OK
compression was tested > OK

Faulty parts:

MAP sensor
exhaust flex was leaking heavily

Just delivered them a used MAP sensor which I bought from mr2-ben.co.uk, now awaiting the exhaust part which i bought in Germany.

[Peter Gidden]

MAP sensor

Unusual.

[Laurens PNut]

Impossible?

[Peter Gidden]

Impossible?

No, they fail occassionally. But the MAP sensor is resonsible for fueling, so i'd expect lots of black smoke, or stalling.

[Laurens PNut]

We will see what happens after it is replaced then

[Laurens PNut]

Dealer replaced MAP sensor, not improved enough to pass the emissiontest...
They now want to replace the downpipe due to a leaking flex.

Could that be it?
Im almost thinking that welding in a universal cat will solve the problem rightaway...

[Laurens PNut]

Bump? Anyone? It's driving me nuts...
I am planning on replacing the cone air filter because it's dirty, pouring in some injector cleaner...

[Peter Gidden]

Injector cleaner will do nothing.

This is not a diffcult issue to fix.

What are your emmissions test figures?

[Laurens PNut]

Will go after the figures.
But could you give me some hints on where to look for if it should be an easy fix?

[Laurens PNut]

Just spoke to the dealer again, they will make a copy of the emissiontest.
They also keep saying that fixing the exhaust (flexi-part) should cure the high idle CO... I doubt it but we will see.

[Peter Gidden]

A leaking exhaust can easily affect emisions.

Pointless trying to get the car working correctly when you have obvious faults.

[Laurens PNut]

Problem is fixed, thnx everyone for their input

[Torero]

Glad to hear it must be a big relief.

What was the solution Lauren? Did you just replace the downpipe?

[Laurens PNut]

Don't know what eventually fixed the issue, I think the major issue was the downpipe in the end.