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2000 Rolla-Poor/stumbling Idle Saga



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NILLINOIS

So my 2000 CE ( 144k) started having the 'poor cold idle and acceleration' problem. Found its usually due to either

1)dirty MAF sensor

2)coked up/dirty Idle air control valve or throttle body

3) Leaking Intake Manifold gasket.

I sprayed some carb cleaner around the intake manifold when the car was idling. No change, so gasket is still good.

I worked in the order of ease, first cleaned out the throttle body and plate. No difference

Next, I cleaned the MAF sensor with throttle body cleaner ( yes, you CAN use throttle body cleaner on these, as they are hot wire, not hot film. Still bad idle.

Next, I installed a brande new MAF sensor. Still bad idle.

Next, I removed the throttle body and cleaned it very well. I also removed the 4 incredibly stubborn phillips screws holding the IAC valve on ( to change the coolant gasket and clean the IAC valve better. Yes is was incredibly dirty in there, and the plate was hard to move. Those 4 screws were impossible for me to get off! I soaked them in PB blaster, and used a bit of heat from a butane torch. I was forced to bring them into my mech who used air tool, and still 2 of the screws broke off. After reassembly w/clean as a whistle IAC valve and coolant gasket. The bad

idle seems to be fixed, but now the acceleration is very stumbling even when the engine is warmed up.

BTW why Toyota chooses to design their IAC valve so coolant goes through it is beyond me. I did read in a blog somewhere that the design 'increases efficiencey'.

Don't know why.

I'll have to also note due to my stupidity, i removed the nut holding the throttle cable guide on the throttle body, as I thought i'd have to remove it since I couldn't get the throttle cables off the plastic guide bracket. It seems a previous owner or mech used silicone or glue on the metal cylinder ends to hold the cables in place

I finally used alot of force and got both cables removed, but forgot i had removed the nut so the the plastic guide fell off, along with the 2 springs.

It turns out these 2 springs are very difficult to reinstall properly, as one of them holds the throttle plate open just a little bit on idle. I couldnt find any diagrams to put the springs back on, so i just 'guessed' their correct installation, which would hold the throttle place shut and provide enough tension to close the plate.

I also replaced the intake manifold gasket anyway, since I had everything else off, and i've read this model gasket start leaking air anyways

After I got everything back together, including new throttle body gasket. The car is even worse than before. So i gave up and took it into my mech, who tried over 30 mins to diagnose it, but couldn't. He said i should just get a new throttle body at a junkyard and put that in, because of the springs being calibrated incorrectly, which he couldn't do, only the dealer, who would probably charge at least $600 for new throttle body. So now i'll have a dirty throttle body again, but hopefully the car will be idling correctly again.

If someone has the diagrams or service manual pages on the correct procedure to re-installed the throttle cable guide bracket and springs, i'd much appreciate it.

Yeah, heating up the throttlebody with engine coolant is more for emissions and robust running. Major function is to prevent throttlebody icing. Even in moderately cool weather, if the humidity is high enough, that drop in pressure inside the throttlebody can cause that moisture laden air to freeze inside. Eventually will choke off airflow to the engine.

It running worse with the new intake manifold gasket is weird - make sure all the vacuum lines are plugged in. No calibrated springs on the TB - this isn't a DBW setup, all cables - so not sure why the mechanic wanted to bail. Possible he didn't want to get involved in a potential electrical diagnostic blackhole.

To me, this sounds like a combination of the TPS sensor is buggered up / cable freeplay is not setup - might want to put an OBD-II real-time datalogger on there and see what the values are being reported. Also, if WOT performance seems OK, but idle and off-idle performance is terrible - could be the upstream O2 sensor dying on you. Under WOT - the ECM ignores the readings from the O2 sensor. If it still acts weird under WOT - then you've got it isolated to the TB and the TPS/cable. The TPS is telling the ECM it is cracked open xx amount, but the MAF and O2 sensors are reporting back different values than expected. Car drops to a limp mode and can run like crap.

Something with the VVT-i system is also a possiblity. Valve overlap/ timing could be messed up - causing poor performance.

I'll try and see if I can get those pages - might have a copy sitting on my other machine.

NILLINOIS

thanks for the reply fish..

So the mech has had it for almost a week, He told me his tech was having problem diagnosing it.

He claims he replaced the spark plugs ( i had almost brand new NGK V-Power set in it ), replaced the

MAF sensor ( I had just replaced it before bringing it in ) and replaced

2 fuel injectors, and the car is running better, but he still wants to do some more tests on it. The engine was

stumbling before and after i replaced the plugs..so i don't think they had anything to do with the problem.

I've never heard of fuel injectors not operating properly until the engine is at operating temp. If they are clogged or

partially functioning, would having them 'hotter' have them operate better?

Im giving him the benefit of the doubt, as the car was exhibiting symptoms of a bad or poorly operating IACV. Will see what he says

next week after more testing.

Yeah, I've never heard of injectors having to get up to temperature to operate correctly. Should be good to go right from the moment you start the car. Possible that the clogs are clearing themselves after some finite amount of time. The injectors can be cycled off the car to see if they are filled with gum/varnish or if the holes in the front are clogged.

I would lean more to the IACV or other issue with the throttlebody - but might be worthwhile to see what they come up with.

NILLINOIS

`Alright, new report. My usual mech had to bail on it, but didn't charge me. He said to get dealer diagnosis and he'd fix it for me.

My sister decided to have a friends mech look at it ( he works at GM dealership ). He scoped it and said its probably combination of

2 things:

1) bad plugs ( I installed brand new NGK V-Powers w/correct gap .044 ), he installed some NGK Iridiums and that improved it significantly.

2) bad cat coverter - he said the computer is dumping more fuel that needed because of downstream o2 sensor.

I can't believe the plugs were to blame for all this..I know that IACV was filthy, so perhaps this was 2 things causing 1 problem. It had a very rough idle even before i changed the plugs from some 3yr old Iridiums to the V-Power plugs. I guess Corollas will run best on them. We will replace the cat and see it that improves things further.

How did the plugs look - were they pretty dirty when he removed them? Plugs can get fouled almost immediately, plugs might have still been OK, just needed to blast them out on the freeway for a couple of minutes. New plugs almost always run better until they get a couple of miles on them - only thing with Iridiums is that they tend to run more consistently over their life, where other plugs tend to degrade linearly over their lifespan. The fine wire ones also tend to "spark" with the least amount of power from the coils.

Converter could be bad - you are at the right mileage and age for a catalytic converter to potentially be bad. Not sure why they mentioned the downstream O2 sensor. It is far more likely that the downstream O2 sensor is going bad, than the cat converter - unless you are one of the lucky ones that have a excessively oil consuming Corolla. The infamous P0420 - low cat efficiency code, 9/10 times - it is a bad downstream O2 sensor and/or exhaust leak than a bad converter.

Bad converters generally don't hurt idle unless the monolith structure is completely clogged up - which can be hard to do, unless you have excessive oil consumption.

NILLINOIS

Turns out that you were right fish..

It seems this was caused by a clogged up cat, we had it replaced and the problem seems to have disappeared, but the

infamous P0171 problem now shows up. I'm attempting to replace both 02 sensors, which, in the case of this particular

model year on the 8th gen, is MUCH harder than it appears. ( See my new post 'Problem removing upstream o2 sensor' )