Cold Start/Idle Issue 92 Toyota Tarago/Previa TCR

[David]

Hey guys,

Vehicle is an aussie delivered 1992 Toyota Tarago, 2.4L 2TZ, Automatic in the GLi spec.

Just a brief history, car ran fine previous to replacing intake pipe and ‘cleaning’ intake. Spark plugs, leads, cap, rotor, fuel filter, oil filter, air filter have been changed within the last 6 months.

I recently replaced the intake pipe on my 92 Tarago, and at the same time I sprayed some Nulon foaming intake cleaner into the intake to try and clean the throttle plate as well as into the intake itself.

After changing the pipe and putting everything back together it was a bit difficult to start. Which I assumed was just the intake cleaner.

However, the next morning it would not start and run on its own. The engine would start and run and sputter for about a second and die. This would keep happening if you kept on trying. If I applied a bit of throttle while starting to keep the revs up it will start and run as long as you still have your foot on the accelerator. After you let it warm up a bit it will idle on its own but it will idle very low at about 600rpm. If it fully warms up it will go up to 800rpm.

Normally on a cold start or semi-cold start the engine will high idle at about 1100rpm and then drop down after driving it for a while. Driveability when warm is same as before smooth and strong. Only issue when warm is engine won’t idle up for power loads (ie headlights), or A/C.

Long story short. Took off IAC to clean with carb cleaner and make sure it is moving. Played with the adjustment screw on the throttle body (I believe it ended back up to where it was originally). I then believe I found one of if not the original problem. One wire in the TPS loom had gone open which was the IDL circuit to let the ECU know when the throttle is shut. So I repaired that and checked all the TPS values against specifications on the ECU connector side and they all checked out. Now after that repair I can hear a click from the A/C idle up valve but the idle does not jump up enough to keep the engine smooth with the A/C on.

Swapped in a wrecker IAC which I bench tested and that made no difference. Then swapped in a TPS from the same vehicle all calibrated and checked within spec. Same issue.

I can also hear an air sound, kind of like blowing through a straw. I tracked the sound to the A/C idle up valve but it didn’t make a difference to the issue with both lines clamped off.

The cold start issue is similar to trying to start a toyota vehicle with the AFM plugged in electrically but not hooked up to the intake pipe.

Also I have tried disconnecting the battery to reset the ECU several times and it doesn’t make a difference.

TL;DR
*Replaced cracked Intake pipe/sprayed Nulon foaming intake cleaner into intake with TB open.
*Car no longer starts when cold unless given throttle to warm up.
*Car no longer fast idles (1100rpm)when cold.
*Car no longer idles up for A/C or power draw.
*Can hear air sound almost like a sucking through straw sound.
*Warm driveability is unaffected.
*Found open in TPS wiring on IDL line. Wire has been replaced.
*TPS wiring checks out fine on ECU connector side.
*Replaced IAC with wrecker IAC from a 93.
*Replaced TB gasket.
*Replaced TPS with wrecker TPS also from a 93 (adjusted and checked resistances to spec)
*Issue still present.

Let me know what you guys think.

Cheers from down under!

Topic

[Brian]

I have a few thoughts on this. When you did all that cleaning, could some of the dirt fell loose deeper into the engine?
Did you clean the throttle body butterfly, aka throttle plate?
If the throttle body plate had a build up on the top or bottom, it will cause odd stalling.
Toyotas have a 3 part egr system. An eye valve, egr vacuum transducer and a vacuum switching valve. Double check all the electrical connections, but pay attention to the vacuum lines. If the rubber hoses are old, they
crack easily. If they are not removed, but moved or bumped during other repairs they can become cracked or break.
You should double check for any and all vacuum leaks about the engine.
If your particular engine is designed to run with a mass air flow sensor, you can clean it but be careful to use the specific kind of spray cleaner made for it. The wire in the middle of it is very thin and fragile.
Has the cam position sensor been unplugged? Double check that connection.
Some spray cleaners and foam cleaners can damage the exhaust system. Some can damage the oxygen sensors and damage the catalytic converter. The converter can be pressure tested at an exhaust specialist. Exhaust shops where I live do that for free. I can’t imagine it would have too high a cost if there is a charge where you are.
I mention the exhaust also just in case some dirt and grime passed through to that system and is causing blockage which would also cause issues as you describe them.
I hope this helps.

[David]

thanks for the reply!

The actual throttle valve itself wasn’t too dirty but most of the cleaning I did to it was after this issue when I had taken it off again. The inside of the intake manifold seemed about the same after the cleaner application so I’m not sure if that would have caused an issue.

When I was spraying the intake cleaner into the intake I do believe some may have gotten all over the EGR valve on the inside of the manifold. But the outside part has not been touched as it is at the back of the intake.

I tried checking for vacuum leaks via spraying carb cleaner as what I saw in Erics video but I couldn’t seem to find any. My tube and ear method only found the air “running” through the A/C idle up valve. I tried to listen for vacuum leaks and couldn’t find any.

This vehicle has a mechanical vane style air flow meter which I suspect may be getting stuck.

This vehicle doesn’t have a CPS as such, but has a sensor in the distributor which has not been touched when this issue came up.

I don’t think its an exhaust blockage since when the engine is warm the vehicle drives fine.

I did purchase a vacuum tester. However, the one I got did not zero and not sure of it’s accuracy. But from what it showed was about 22 in-Hg at idle, and when the throttle was snapped open and shut it would go to “0” and then past 22 to maybe 25 or more then back to 22. The needle did jiggle but when I tested it the engine wasn’t idling smoothly.

[Author]

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