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I’m new to the ETCG forums, but I’ve watched and enjoyed Eric videos since discovering them a few months ago. I’m very thankful for the advice he offers and hope that I might be able to get some help from the community with my rough idle. I’m certainly an amateur when it comes to auto repair, but I’m not afraid to get dirty. Change my own fluids, brakes, basic diagnosis, etc., but I’m stumped here.
Allow me to provide some background that may or may not have contributed to my rough idle problem. My apologies for the long post, but I want to make sure I’m providing as much detail as possible to assist those who are so graciously assisting me.
Some history: I noticed a large amount of corrosion on my positive battery post about three weeks ago. I’m talking about the size of a fist, perhaps more. It’s unfortunately one of those things I never really kept an eye on until recently. Anyway, I went about the process of cleaning it with some baking soda, warm water and a toothbrush. I removed almost all of it, creating no small mess in the process. However, there was enough corrosion between the post and the terminal on the end of the wire that I couldn’t actually remove it from the post to finish the job. I let it be for a while until recently when I attacked it again. After some serious elbow grease, I was able to remove the wire and finish the job. Or so I thought.
That night, the car gave me a no crank/no start. The following morning I was able to see that some of my baking soda/water solution had seriously fouled the terminal on the end of the wire, so much so as to prevent a circuit from forming from the terminal to the wire. I removed the terminal from the wire, got it into the house to clean it up, put it back on the wire, tightened the terminals to the posts and she started up as always. Now, enter my problem:
The battery was a little drained (12.46V, normally reads at 12.68V or so) from a few unsuccessful starting attempts (before completely removing and cleaning the terminal), so I was letting it run for a few minutes to charge the battery. After 3-4 minutes of idling from a cold start, the rough idle began. Quite rough actually – enough to shake the engine within the compartment, vibrating anything and everything in the car. Gave it some gas, and it was perfectly fine. Off the gas, and it ran like a sick dog. No check engine light.
Did some poking around (including on the ETCG website in the rough idle section) and figured the most likely culprit was the mass airflow sensor. The airbox got pretty dirty from battery crud being slopped about, I figured it plausible that the sensor was fouled. Cleaned the sensor with the appropriate cleaner, let it dry, reinstalled, no joy.
I headed back to the parts store for a remanufactured OEM sensor. Even managed to forget the old one, so I paid the core charge too. Ugh. Before installing the new sensor, I got the bright idea to unplug the old one, trying to bypass it. I read that on some cars it’s possible to bypass the MAF by unplugging it; in theory if it will run smoothly (though not efficiently) without the sensor providing data, you’ve found your problem. Unplugged it, turned it over, and it wouldn’t catch. Immediately threw a check engine light, certainly to be expected. Not able to isolate the MAF as the problem, I swapped parts. Started up and ran fine for at least 5-6 minutes, longer than it took to present the problem previously. Problem solved?
As I am currently without a code reader (not even a little crappy one), I just disconnected the battery to clear the code. Big mistake, I think. After half an hour or so, hooked the battery back up and the problem returned within a minute or so of starting. I turned it off and it has sat ever since.
Again, my apologies for the novel of a post. Thank you in advance for any advice that you can offer.
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Check your battery ground and engine ground. These can break or corrode to the degree where a connection is impossible. No ground, no circuit.
After verifying grounds check for vacuum leak, spark and fuel. What is the code stored? Any auto parts store should be able to tell you. A maf sensor is a symptom, not necessarily the cause of the code. It’s like a human body…A cough is a symptom, the cause is bronchitis. Cough syrup will help the cough bit won’t take care of the bronchitis. Check air filter, throttle body, put a vacuum gauge on it at note the needle at idle and when you slap the throttle open. It may be choking itself out due to an exhaust restriction.
Contact the dealership… This year had a bad batch of ECMs that caused all kinds of issues…. However, this repair/replacement of ECM service may have been done and you may have another issue… I think it was TSB #05306 or #04205….
Address what is going on with the Check Engine Light (Let us know what code is being thrown)…
I would clean the throttle body and start it and drive it. The idle speed may just need to relearn since you disconnected the battery.
It only threw a code when I unplugged the MAF. There was never a code before that point, and the code has been cleared now after I disconnected the battery.
Air filters have been changed regularly, and I looked it over when swapping the MAF sensors. Standard level of funk for an air filter.
I’ve read that a few drive cycles can produce a code or clear it if the problem was resolved. What time/distance constitutes a drive cycle as far as the ECM is concerned? I don’t want to stray too far from home with it idling so poorly.
Here is the drive cycle info, but I would advise you continue to look elsewhere for the issue…. Good suggestions have already been made
– Two (2) minutes or more passed after the engine start.
– The Engine Coolant Temperature (ECT) is 167°F (75°C) or more.
– Cumulative running time at 30 mph (48 km/h) or more exceeds 6 minutes.
– Vehicle is in closed loop.
– The fuel-cut is operated for 8 seconds or more (for Rear O2S Monitor).
A. Allow the engine to idle for two minutes.
B. Warm up the engine until the Engine Coolant Temperature (ECT) reaches 167°F (75°C).
C. Drive the vehicle over 30 mph (48 km/h) for more than 40 seconds.
D. Stop the vehicle and allow the engine to idle for more than 20 seconds.
E. Repeat steps C and D at least 8 times in one driving cycle. (Do not cycle the ignition key.)
-Karl
Ok so think about what you’ve done…you have probably either have a bad terminal, bad connection between cable and terminal or you have blown a fuse or shorted the battery. Easiest thing to do is check all your fuses, check the terminals and cables and make sure you have good contact and try and run it with a different battery
Alright, I’m back, and with good news! I did some fairly extensive research here and on other forums to narrow down some likely causes. Vacuum testing (propane enrichment) yielded no results, which was somewhat surprising as these Corollas are apparently known for the original intake manifold gaskets going bad in the winter. Turns out disconnecting the battery to clear the code wasn’t a horrific thing, but it did reset the ECM, so all of the fuel trim data was lost. As such, it went back to factory defaults, except the throttle body has some 70K miles of crud on it, so the default settling was out a bit out of whack.
With extreme caution, I cleaned the throttle body and the plate. I never really opened the plate, but cracked it what felt like 2mm to get at the bottom end of it. There was very little dirt/fouling in there, but apparently it was enough. Took two attempts to start, as I was being impatient and didn’t let it dry. Once running, it felt just fine. Drove it around the neighborhood for a few minutes and felt no ill effects.
My thanks to all of you who posted with advice. I sincerely appreciate it. Happy New Year everyone!
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