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By TomGibson, February 11, 2015

I have a 2000 Corolla that has been having problems. While idling it vibrates, and a friend said it looks and sounds like it's missing. When I put it in drive or reverse the idle seems to lower a bit and gets more rough. There is also some hesitation when I start to accelerate. While I'm actively accelerating the engine seems to smooth out. Actually any time I increase the rpms it seems to smoothe out. When I lift my foot off the accelerator I can feel the vibration start again, but nowhere near as rough as when I've stopped or almost stopped. After driving a bit, particularly after driving on a freeway and the engine is warm, coming to a stop can make it stall. I can sometimes switch to neutral before it stalls, and when it's time to go again I have to rev the engine slightly before or just when I switch back to drive or reverse to prevent it from stalling, but that doesn't always work. It feels like the engine speed drops too low and it stalls. Needless to say this is a pain when I have to stop at a store on the way home, stalling when I park, again when I back out, again when I try to go... A friend helped me change the spark plugs a week ago, and I cleaned the MAF sensor, but the problem persists. Any ideas? I've also noticed a sound that pops up sometimes. It increases in pitch with the speed of the car, and I can only hear it while I'm accelerating. Someone suggested a vacuum leak, but I don't know how to check for that.

Oh, I also have an oil leak, not sure if it's related. It seems to be leaking from the back side of the engine, towards the passenger side. We changed the valve cover gasket hoping that would stop the leak, but no such luck. Well, it was also leaking into one of the spark plug holes, but just a little, and that seems to have stopped after the gasket change. While we had the valve cover off he mentioned that the timing chain seemed a little loose, but we didn't want to mess with it until we know more.

I've had the car for 9 years and have only recently been learning about properly maintaining it. I'm eager to learn more though, so any help is greatly appreciated.

You didn't mention the mileage - I'm assuming this car has over 100K miles, possibly 200K miles on it? What was the previous maintenance history of the car, any other issues with the car, aside from what you posted - like oil consumption, smoke on startup, hard to start, poor fuel economy, etc.?

A good throttle body cleaning could help here, especially for your idle issues. Possible that the throttle cable is misaligned and/or the TPS sensor is faulty. But I'd start with cleaning the TB first before you run down those other issues.

Whining noise when accelerating, could be pointing to a number of things - some of which could be related to your issues. Assuming that the battery is not more than 5 years old? Could be a the charging system is too weak - this would put an increased strain on the engine, which could cause it to stall. This family of engines is also very sensitive to electrical noise - double check battery connections are clean and tight, check chassis ground points, make sure they are clean and making good contact.

Gummed up injectors could be another possibility. If they are really clogged, nothing short of removing them and cleaning them mechanically will work. In the mean time - try running one of those in-tank cleaners. Make sure it has a lot of PEA additives - Redline Fuel System cleaner has some of the most out there at about 50% of the bottle, but can be hard to find. Chevron Techron Fuel system cleaner and Gumout Fuel system cleaner w/Reagane also have some amount of PEA.

Leak on the engine could be from the timing chain tensioner. Very common occurrence on cars with variable valve timing, like your 2000 Corolla. It is a relatively easy fix - usually it is the o-ring on the tensioner that goes bad. Most owners opt to replace the whole assembly - tensioner + o-ring can be had for about $25-$30.

Mileage is about 150K. As far as maintenance I've only had a few oil / oil filer changes, and I've replaced the air filter, most recently last month. I bought some NGK Iridium IX plugs after seeing the look on my friends face when he realized I hadn't even checked the plugs in the 9 years that I've owned the car. I've also cleaned the MAF sensor, once last year and again last month. Other than that I just check to make sure I have enough oil. Here's a pic of the old plugs:

I'm not sure if I have oil consumption, just know for certain that I have a leak. Mileage has varied between 20 and 24 mpg for as long as I've owned it, not sure if that's good, bad or average.

I haven't noticed any smoke on startup, or anytime really. I do have what looks like soot built up on the bumper above the exhaust, but I don't know if that's just because I haven't washed it in a long time or what.

The battery is about a month old, my old one needed to be replaced after almost 4 years.

It starts just fine, even after it stalls. However, after driving a lot, particularly after driving on the freeway is when it stalls the most. If I stop somewhere, like at a store, the car often won't start unless I let it sit there for anywhere from 2-15 minutes. However, if it stalls and I immediate try to start it it will start just fine. It's like letting it sit off for a few minutes makes it not want to start until it's had a chance to cool or something. Today a nearby tow truck operator offered to get it started for me by spraying ether into the air intake. I hesitantly agreed, and he sprayed Hot Shot Starter Fluid into the hole in the airbox cover, closed it and had me start it, and it worked. If I do have a vacuum leak, and that makes the air/fuel mixture lean, does spraying that fluid into the air intake then help to correct the air/fuel ratio? Or does the fact that it worked mean that a vacuum leak isn't the problem?

Is there a good tutorial on cleaning the TB for my engine?

Thank you for your help default_smile

Lord almighty that top plug is gonna gimme nightmares

I used Redline SI-1. I also checked my coolant, and it was very low, so I filled it up. I've been checking the radiator every morning since and it still looks full, can't really see the level in the plastic reservoir though. At the same time I checked the vacuum hose connections just to make sure they were actually attached.

I have no idea what made it get better, but it's definitely better. I've driven about 150 miles and so far I've only stalled once, and have only had it idle rough enough to make me switch to neutral three times, but it does still shake while idling, just not as bad. A few times it actually idled so low and smooth at a stop light that I thought it had stalled. Also, it still has the problem of staring when hot. If it's only off for a short time it will start. If I leave it off for somewhere between 5 and 15 minutes, it won't start unless I wait a while longer, like it needs to cool down or something, unless I use starting fluid.

That hard to start when behavior is pretty peculiar. Is it that the engine won't fire at all - just have to let it cool down, or it fires but immediately dies, or is it that long cranking with the engine almost catching, but not quite?

Those can be signs of vapor lock - but that is pretty much made non-existent with EFI and return-less fuel systems, like the one in your Corolla. It is possible that it is something pretty simple, like a maintenance thing. Might even "fix" itself, once you start to drive the car more and more. Could be a clogged IAC valve on the throttle body, could be a bad upstream O2 sensor, could be faulty wiring running to the fuel pump, even a bad tank of gas.

Given the seemingly long runs on some maintenance items - I'd put my money on just getting all the fluids changed out, find all the leaks and fix them - keep an eye on fluid levels. The new plugs probably helped blow out whatever was in there. Be a good idea pull them and see if they gotten fouled or not. Also, given the age and mileage - you are close to the O2 sensor life span. Some have gotten a huge amount of mileage out of the original sensor - some had them die out very early. Since your fuel economy is a little on the low side - could be that the O2 sensor is slowly dying on you. A dying or lazy sensor will not throw a code - but can make the car run lousy. Also look into cleaning the MAF sensor (on all Corollas model year 2000+) and associated IAT sensor. The module is in the top of the airbox. There isn't any maintenance schedule for that sensor - the book just recommend replacing it. But many owners found that cleaning it gave them very good results. You can look up how to clean the MAF sensor on this forum and online - lots of DIY guides out there.

When you said the coolant was low - was it low in the external coolant reservoir tank or was it actually low in the radiator? Just keep what you have been doing, keep an eye on the coolant levels - pretty unusual for coolant to go missing, as the system was designed not to lose it readily. Hoping it is not a water-jacket / head gasket issue - as that can cause all sorts of headaches for you. Same goes with engine oil - if your Corolla is one of those that consumes an excessive amount of oil - keep it topped off as often as possible.

Sigh, it was running better, but the last two days it got a little worse, and today it actually stalled multiple times again. I'm wondering if checking the vacuum hose connections may have tightened something that has since worked itself loose? Anyways...

The not starting: the starter turns the engine over, but that's it. It's like it just spins. After a while of cooling it will kind of rumble a bit like it wants to start when cranking for a while, but I still have to wait longer and let it cool more. Eventually it will crank, sound like it's almost catching then eventually fire up.

I've cleaned the MAF, that's one of the first things I learned to do. The coolant was low in the actual radiator, but since I filled it up it hasn't gone down at all in the radiator. Like I said though I can't really see how much is in the external reservoir.

How much oil does it consume? Your old plugs' residue is evidence of excessive oil burning... It'd be good to get compression readings.

My engine has ignition coils, as far as I know there aren't spark plug wires. Do the wires to the ignition coils ever need to be changed?

Not sure how much oil it consumes, I also have the leak. I should be able to test the compression the weekend after I get paid in about two weeks. Can I use the same equipment to test the compression AND the fuel pressure?

I noticed today that the idle gets worse when I turn on the ac. It's rough, then I turn on the ac and it drops and feels like it's going to stall.

Also, I didn't get to work on it this past weekend as planned, my fiancé needed the car Saturday, and it rained all day Sunday.

That the idle drops so low when you kick on the AC, that sounds like an issue with the IAC valve sticking on you. Might be worth giving the throttlebody a good cleaning. IAC valve is held on with some funny screws - looks like a torx, but they have 5-points instead of 6-points.

Sometimes, those coil on plug igniters can just plain die - for some owners, they run 100K-200K miles on the igniter - no problems. I've heard of other owners going through them quickly, every 30K or so, some are on their 3rd or 4th set!

As for using the same gauge for compression and fuel testing - it is possible. Usually compression gauges have markings to line up with typical compression readings - ie, 150-250PSI sort of range. Typical fuel pressure gauges read in the ten's of PSI - 30-60PSI range. It would work, as long as the gauge can resolve that level of PSI. These tools, you should be able to rent from an autoparts store - no need to buy a set unless you want to add to your tools collection.

I'll have to find a driver for the screws on the iac, but I was able to do a quick on car cleaning of the TB. Twas pretty dirty, especially around the pcv port. There seems to be a little less hesitation, and better acceleration, but it still has a tendency to idle too low, and actually stalled when I slowed and try to make a u-turn. Running the AC and turning the wheel all the way both seem to make it idle so low that it can stall. I'll be removing and cleaning the IAC next, and hopefully cleaning or replacing the pcv valve while I'm in there.

Do you know the name of the type of screw that's holding the iac on?

Here's a pic of my dirty TB.

There should be a number of videos online that show how to clean the IAC - if you want get some more info on it. Sometimes, even with some healthy scrubbing - the IAC will still stick. Some have resorted to soaking the whole throttlebody (sans electrical bits) in solvent to try and clean it up. Some have gone so far as to drill a couple of small holes in the throttle plate to help with adding more air (old school trick, especially on TBI setups).

To be clear, the IAC is on the bottom of the TB in this picture, but it looks like it has two parts. Am I just removing the part that sticks out to the left? (the part with the screw heads facing left) Or also the part that is attached directly under the TB? (with screw heads facing down) Would either require me to remove the TB? Also, do I need to worry about replacing gaskets? The videos I've found so far just show the people spraying the valve, which looks different in each video, making me wonder if some are only removing the part sticking out to the side.

Yup, just remove the part that sticks out (screws are facing out). Probably easiest to remove the TB to get at it. Gaskets, as long as you are careful and not damage them, can be reused. You can order some from the dealership for relatively little money, but when I did mine - the dealership had to order the gaskets - didn't have them on hand. Once you have it off - it will be pretty obvious if the IACV is the culprit, as that cavity could be completely packed with carbon and varnish, not allowing the solenoid to rotate the valve.

I've been putting off removing the iac until I can get a gasket, just in case. I started the engine last night and sprayed water on the vacuum hoses, TB, intake manifold and such, but couldn't find a leak. I did notice though that while the engine is cool, it starts and idles fine as long as I leave it in park or neutral. As it warmed up I could hear the idle starting to slow, then speeding back up in a rhythm. The warmer the engine got, the lower the idle would drop. When it got to working temp it dropped so low it was shaking, and eventually stalled. But today while driving I put it in neutral at stoplight and while it still idled up and down, it only got low enough to shake when I forgot to switch it to neutral. While idling at stoplight I tried switching the ac on and off, but idle would either not change at all, or would drop a little when the ac turned on. I didn't use the freeway today, but when I used it yesterday I occasionally had to put a little pressure on the accelerator to keep the idle from dropping too low.

I still have the problems starting it while hot. I also got my codes read: 0300, 0303 and 0304. I tried swapping the ignition coils between 3 and 1, and between 4 and 2, but I still had the same codes pop up, so the coils don't seem to be the problem(unless I'm missing something). I had a 0420 when I checked the other day, but it hasn't come back.

I've also noticed that my mileage has dropped for the last two tanks.

Thank you for all your help with this, it is greatly appreciated.

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