Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

97 Corolla, Rough Idle, Stalling Noises

I have a 1997 Corolla with 150k miles.

I had my catalytic converter and flex pipe replaced this summer. Lately, my car has been idling rough. While stuck in some horrific stop and go traffic three weeks ago, it started to make noises as if it would stall out. It didn’t, but it still sometimes makes those noises.

The car seems fine on the highway. No loss of power. I did think that the hood felt too warm on a recent trip, but the temperature gauge in the car showed no issue.

The car hesitated when I tried to start it last week, but normally starts fine. It was the first cold day of the year.

I saw some white smoke come out of the tailpipe last week. It only happened once. Coolant and oil levels are fine. The spark plugs look good.

The fill pipe has been leaking gas for several months. It leaks if the tank is more than half full and it drips a bit of gas when I fill up. Two mechanics have not been able to find the leak and have told me not to replace it until it is a problem, given the age of my car.

I took it to a mechanic today (not the one who replaced the cat). He told me that the rough idling is due to the new flex pipe being shorter than what was originally there. He assured me that the car is fine to drive long distances and that there was nothing wrong with it. There’s no check engine light or anything on the dash to indicate a problem.

I should be relieved, but I’m not. I’ve lost confidence in my car. Can the stalling noises and rough idling be explained away by a changed exhaust system? Or are these signs of a problem about to happen?

A slow rough idle or random stalling at idle can be due to a vacuum leak (easily checked with a vacuum gauge) or an Idle Air Control valve that is acting up.
An IAC valve problem can occur without triggering the Check Engine Light or setting any codes.

You should take that statement about the cause of this being due to a shorter flex pipe with a grain of salt.

Have you tried to clean your throttle body out yet? Also might be a good time to clean your Mass air flow sensor(MAF) with MAF cleaner, don’t use throttle body cleaner.

Thank you, I’ll look into these things. I did some more investigating last night and confirmed that the rough idling is at it’s worst when I am in reverse.

With my early 90’s Corolla there’s a couple of things which are supposed to increase the idle speed. Like when you turn the steering wheel (with power steering), the idle speed increases. Or turn on the headlights. Or turn on the rear window defroster.

After the engine is warmed up, pull over into a quiet parking lot and listen. Does the engine increase idle speed when you do each of those?

A partly stuck open EGR can cause this symptom too. Along with quite a few other things, but those above (including the other posts too) are a good place to start. Best of luck.

Thank you all so much for your help! Just a quick update for other people who might be having similar issues.

I had to replace the battery this weekend. The car drives much better than it has over the past few months. The rough idling seems 95% cured. The battery was due for a change, but it never occurred to me that it could cause issues with the idle.

Perhaps the car needed to be rebooted to sort out the idle issues? Or maybe the dying battery has a negative effect on idling?

I had a high idle problem with my '88 Toyota Supra. Before I could find and fix that problem, I had an electrical issue pop up that needed attention first, and I had to disconnect the battery for a short time to fix that. When I reconnected the battery, the idle problem was fixed. I also assume that the car just needed a reboot.