Corolla Conundrum

I have a 91 Corolla with a 4A-FE engine & auto trans with 135,000 miles. Car idles fine and when in park or neutral, I can hit the gas pedal and engine revs fine. Problem is when in drive, there is hesitation/sputtering when accelerating. It seems to get worst as the car warms up. It backfires occasionally if I step on it to merge with traffic. Dist cap, rotor, plugs, and wires have about 20,000 miles. I replaced the fuel filter and ran seafoam in a tank of gas. Also air filter was replaced. The check engine light is not on and mpg has reduced significantly. It’s a great car and I have maintained it well(oil changes, tranny fluid and filter, Brakes and fluid, half shafts, new radiator etc.)

Possibly, the ignition coil has failed. Here are the instructions on how to check the ignition coil . You will need an electrical test meter (multimeter). Walmart has them for under $25. This is a LOT cheaper than changing parts, unnecessarily.

I have to wonder if his catalytic converter has failed since the problem worsens as the car warms up. As with any car you have to establish the basics no matter how unlikely the problem could be. I’d want a test of fuel pressure and spark delivery. Whenever someones mentions backfiring my initial reaction is that there’s a problem with the ignition timing, which in turn can mess with the converter. Here’s the easiest thing to do: take a drive at night and really floor the car and get it nice and hot when the car is acting up. I mean really get on the gas for a bit and then quickly pull off the road and look underneath and see if the catalytic converter is glowing red. If it is the converter is toast.

Now a converter can still be faulty an not glow red, but if it does, it makes troubleshooting a lot quicker. In summary check fuel pressure, check ignition timing and check the converter.

You may want to revisit your plugs. If you use OE plugs, they may only have a projected life of 12-15000 miles.

I tested the coil and found it out of spec. Went ahead and replaced it. While in the distributor, I went ahead and changed the rotor and cap. The cap for this vehicle comes with new wires attached. Also found the plugs looked good but were worn. Should’ve been .032 but were at .038. Replaced plugs (NGK). The “Go-Kart” is back to running like her old self. Thank you hellokit for steering me in the right direction. Also Xebadaih for the heads-up on the plugs. I figured the NGK’s I installed at last tune-up would last more than 20,000 miles. I checked the cat this morning just to make sure and saw no glowing. Again, thanks to all who responded

what about the possibility of the timing belt jumping a gear?