2001 Corolla Rough Idle/Stalling

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zounds
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Joined: Mon Aug 05, 2013 3:09 pm

2001 Corolla Rough Idle/Stalling

Unread post by zounds » Mon May 05, 2014 7:43 pm

My 2001 Corolla has started idling extremely rough when I'm stopped at traffic lights. It happens sporadically and unpredictably. The car shakes and jerks and, if the light doesn't turn green fast enough, stalls. After the second time this happened, the check engine light came on with code P0240 (Catalyst System Efficiency). I brought it to my usual shop who told me the engine was misfiring. They changed my spark plugs and told me I was good to go. The check engine light was off when they returned it to me and I drove it for over 100 miles (mostly highway) over the next few days without it coming back on. After a few days of driving, the rough idling and stalling came back. After having trouble replicating the rough idle I was experiencing, my mechanic eventually found two bad ignition coils. He replaced them, and after driving 2 miles from the shop, the car idled rough and stalled on me again. I brought the car back to the shop. Mechanic seemed baffled, cleaned a few things, repaired some brittle looking vacuum hoses, and told me to bring it back if it does it again. It did it on the drive home. I'm at my wits end, he's at his wits end....any ideas for what could be at fault with new spark plugs, two new ignition coils, and no diagnostic codes coming up? Thanks for your time.

PS - the car has 175,000 miles on it and is an automatic. Runs well besides this problem, though I think it gets worse fuel economy than it should. Maybe the new ignition coils will help with that...

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carriedi
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Re: 2001 Corolla Rough Idle/Stalling

Unread post by carriedi » Mon May 05, 2014 10:59 pm

there are a bunch of things to check for and they need to be checked when the car is acting up. The cat. code may or may not be from the misfires. But lets assume for now that it is.

If the engine is running good while driving but only has a problem at idle, lets check the things that control Idle. If you can scan the vehicle while the rough idle is happening, what does the IAC show that's doing? What is the idle RPM? what are the fuel trims and how does the rear O2 sensor look. You may have to be driving the car with the scanner hooked up so you can duplicate the condition.

Did the car have codes for misfires? Is that why they changed the coils? Has the check engine come back on and does it have codes? If you have had a very bad spark plug or a damaged coil it could cause damage to the computer. The connection for the coils to the harness could also be a problem.

You could also have a bad coolant temp sensor that may intermittently short and cause the engine to get too much fuel at idle. Sometimes you may need to clean or replace the IAC, idle air control solenoid.

The main thing is that before you change any parts find out what is happening and what parts are affected. You may have to drive it with a scanner and graph what the computer sees and what it does to react to what is happening. the scanner should narrow down what cylinders are causing problems. You also may have to use a lab or ignition scope and see what your secondary ignition is doing. Do you have a good spark signal to all the cylinders? Do you have a good signal to the coils? Does it happen when the engine is cold? does it only happen after the engine warms up? Is the rough idle and stall the only problem?

the main thing is that it needs to be looked at when it is acting up. Now these are all things to look at for idle. If you have other things that are happening while under load or while cruising on the highway, there are other things that will come into play.
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zounds
Posts: 12
Joined: Mon Aug 05, 2013 3:09 pm

Re: 2001 Corolla Rough Idle/Stalling

Unread post by zounds » Tue May 06, 2014 9:08 am

Thank you for that thorough response. I unfortunately don't have a scan tool or a scope so unfortunately I can't test these things. I may suggest some of them to my mechanic though, as he really seems stumped. The car did have misfire codes, but the check engine light is not on anymore. Runs great cruising on the highway - this is its only major problem as far as I can tell.

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carriedi
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Re: 2001 Corolla Rough Idle/Stalling

Unread post by carriedi » Wed May 07, 2014 1:18 am

I would look at CTS, TPS, throttle body coking and the IAC first then
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zounds
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Re: 2001 Corolla Rough Idle/Stalling

Unread post by zounds » Wed May 21, 2014 8:41 pm

Just an update for anyone who might have a similar problem: My mechanic thinks the ECM is failing. He says that when it does the rough idle his scanner immediately loses its signal from the ECM - happened 3 times so he's pretty sure of it. He also assured me that TPS, IAC, and the throttle body were all checked already and are working properly.

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carriedi
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Re: 2001 Corolla Rough Idle/Stalling

Unread post by carriedi » Thu May 22, 2014 10:46 pm

make sure all the ground connections are good
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