Corolla 99 Engine Rattles - Corolland: the Toyota Corolla Forums

Hi,

When I start the car the engine runs at 1200 RPM and when it reaches the normal operation temperature it go down to 750 RPM (at P). However, when put the transmission on D without allowing the car to move, the RPM goes down to 620 RPM and the engine start shaking. My car has 130K. I replaced spark plugs and wires and that did not change anything. I also cleaned the Throttle Body and the car now shake less violently. I could not clean the IAC because the screws were rusted I only sprayed Electrical cleaner in the IAC hole in the throttle body. Any suggestions?

Could try running a quality fuel injector cleaner as well - see if that helps improve idle quality, as the injectors might be fouled up with some carbon/varnish.

IAC valve would be something you have to pull apart to clean effectively - just spraying into the opening won't do too much. But definitely not work damaging the whole throttle body in the attempt to take it off. Those screwheads are also hard to take off even when new, as they are 5-point star heads.

You can test the operation of the idle-up circuit by turning on the AC, see if the idle jumps when it turns on. If it does, the IAC is working - if it doesn't or makes little change - then that IAC might be clogged up.

Sometimes, you can get at it by removing the throttlebody and cleaning it off the car. Give you much better access to the bleed hole on the throttle body, also can clean the gunk off the rear of the throttlebody that couldn't be reached before. Could also be a loose throttle cable - too much slack between the cable and the throttle cam can cause it to idle excessively low. I would double check and see how much slop there is in the cable - but keep in mind what you adjusted. Even minute changes can have a huge impact on idle speed. Could easily overshoot and have an excessive high idle.

I tried the idle-up circuit test. When I turn on the AC the RPM change form 650 to 750 for a second then it stays at 700. Does that means it IAC is clogged?. I live in Michigan and everything is rusted. I took TB out and used WD-40 and nothing worked. I found a used TB on Ebay that looks in better condition than my TB. I might consider buying it.

I forget to say that. Before I clean the TB, the car used to idle at 1800 until temperature gauge reaches "C" then it go down to 1200 then it go down again to 750 when it reaches normal operation temperature. Now it idles at 1800 for a second then goes down to 1200 and stays until temperature gauge reaches normal operation temperature ( needle points at the middle). have I broken the IAC or what?

I tried the idle-up circuit test. When I turn on the AC the RPM change form 650 to 750 for a second then it stays at 700. Does that means it IAC is clogged?. I live in Michigan and everything is rusted. I took TB out and used WD-40 and nothing worked. I found a used TB on Ebay that looks in better condition than my TB. I might consider buying it.

Nope - sounds like the IAC is working. It is supposed to bump up the idle slightly with an extra load on the engine.

WD-40 is good for cleaning parts and displacing water, but doesn't really work that great on rusted/corroded parts. Might trying something with a bit more penetrating power - PB Blaster, Kroil, etc.

Thank you fishexpo101 for the information

Make sure you have all your bases covered. Make sure the plugs, plug wires, coil packs are all OK. Injectors are all working (audible check), run quality gasoline only. Check air filter, make sure there are no vacuum leaks, etc.

From your description of the issues - sounds like it just needs a good tune up and a brisk drive down the highway with plenty of WOT applications (so called "Italian tune-up").

Having a spare throttlebody certainly doesn't hurt to have around - but may not help your case. Most of the stuff you have to worry about are "inside" the throttlebody, doesn't really matter how it looks on the outside. Unless the TB is free or very cheap - I wouldn't even give it a second glance. Just concentrate on the one you have - should be able to get the idle to where it needs to go, just by eliminating other possible culprits.

I biught a bottle of seafoam and put around 10 oz in the fuel tank before filling the gas tank. After driving few miles I noticed that the car RPM is bouncing between 750 to 850 while idle. What happen?is this because seafoam and how can I fix it?

How does it bounce between those RPMs? Does it do it smoothly, or is it very abrupt?

Usually, an unsteady idle is from a vacuum leak somewhere. But usually, the jump in RPMs is substantial - something that bounces abruptly from 700-800RPM to 1500-2000RPM - huge RPM swings.

Could also be a clogged or bad injector. Could also be a failing upstream O2 sensor. Hard to say any more until you flush the Seafoam out of the tank.

Just drive normally, empty as much gas out of it as possible (but not too much - too low of a gas level will damage the fuel pump). Fix up with gas from a station that sees lots of business, that usually increase your chance of getting gas that hasn't sit in the underground tanks for too long. See how the car runs then.

Thanks for the advice fishexpo101 . I drove the car today on the highway and when I stopped at the traffic light the symptoms is gone. The RPM used to bounce smoothly like a sinusoidal signal. The gas station that I used was in deserted area that maybe the reason of the problem . I feel the car performance is weaker than before and I Still have the engine rattling problem but now i feel it worse than before. I'll try to remove the IAC from the TB and clean it thoroughly. also i'll check the ignition coils secondary resistance. Also ill check fuel injector resistance and audible. but how can i check the O2 sensor?

O2 sensor - have to backprobe with a scope while the engine is running. Tough to do, practically. Might be able to get away with a datalogging OBD-II scanner. They make a number of them, from $70 to couple of thousand. But that will only report back voltage "snap shots" at the polling rate of the OBD-II on the car - something like a couple of Hz. Not enough resolution for a definitive answer - but better than nothing.

If the RPM varies smoothly and the car seem down on power - very possible the upstream (pre-cat O2 sensor) is going bad. Usually lasts about 60K-100K miles tops - sometimes you can get more out of them, sometimes less. Given the model year of your car - even with low mileage, this is a strong possibility.

If you decide to change it - stick with Denso OEM parts. Lots of people have had issues with non-Denso parts on these cars, seems that the car is pretty picky about what electrical and emissions parts you use. I've used Bosch before with a number of issues - that immediately went away when I used a Denso replacement part.

Before you go too far down this path - make sure you get a full tank of good gas in the car. Lot of the symptoms you are describing can be attributed to a bad tank of gas. If the issues still stay after running a tank of known good gas through - then start diagnosing it further.

Today I checked the ignition coil and injectors resistance and both were with in the spec. limits (according to Haynes). I also removed the IAC from the Throttle body and cleaned it. I had to use hammer to loosen the screws. I couldn't open the actuator because it was so rusty. After starting the car the Idle speed now is 1000 RPM at normal temperature . I could not found any information on how to reduce the idle speed?

Idle speed is set by the ECM. Throttle cable has a screw stop that can also be used to adjust the idle, though I'd see if the ECM can pull the idle down first. Can also try resetting the ECM, so that it relearns operating parameters and see if that fixes the higher idle.

I went to mechanic today and he told me that I need a new engine mounts and that would cost 700$. i just want to know how many engine mounts that corolla 99 has and what are there positions. Can I do it myself.Thanks for advice