Why does my engine(95 galant) stumble during acceleration?

Question

I have a 95 Mitsubishi Galant that I use for work.

It has been having issues with it stumbling while I accelerate for a little while now. But now it will barely accelerate at all.

The plugs, wires and air filter are 2 months old, the cap and rotor I replaced yesterday, along with the fuel filter.

I can hear the fuel pump working before I turn the key to start the car.

Tried some commercial Injector cleaner on a whim, nothing.

I checked the wires for arcing, but saw no signs.

The car idles fine, 90% of the time. Sometimes it drops about 400RPM and sputters but jumps right back to about a 1000Rpm idle.

It used to be that it would simply stumble at lower RPM's but when I got it above 2k it would smooth out and accelerate just fine. But now, I can barely drive the thing.

Any suggestions on what I should check next?

I am going to check the coil and injectors... but I wanted a little more input as to what else the issue could be.

Thanks in advance.

The check engine light comes on, but not when this issue is present.

For the last 4 days the check engine light has been off, but the issue has gotten worse.

There is a hole in the exhaust, right before the upstream O2 sensor, but I wouldn't think that would cause the car to run this poorly.

Checked the Mass Airflow sensor, it looks clean to me. I think I will clean it anyhow, seeing as how it is a thermsistor I will use some standard contact cleaner.

I know the O2 sensor readings would change the mix, but would it cause the car to run so poorly that it has a very hard time going up a hill?


One important detail: When the engine is cool, the problem is not so pronounced. When it gets up to normal operating temperatures, the issue is severe.

Answer 1

the hole in the exhaust is changing what the o2 sensor sees. fix that first. also check MAF (mass air flow) sensor

Answer 2

With and age and mileage, check the airfilter and plugs to see how they look. Airfilter is straight forward, if its dirty replace it! Replacing the plugs may be required. If they look like crap, or are correded replace them. You do not need super expensive plugs either! Don't get tricked into buying a 8-12 dollar plug! Single or Double platniums will do fine. Buy a feeler gauge and check the gap on all new plugs, even if they are pre-gapped. If the plugs appear to be fine, airfilter looks alright. Do an oil change and put in injector cleaner. If all else fails, it may be the O2 sensor. Most people do not realize that if the 02 sensor is failing the ECU (computer) in the car can't compensate for rapid changes in the rpm of the motor, which will cause hesitation!

Answer 3

If the check engine light is on I would take it to get that checked first. ( auto zone will check it for free) If it is not on you might be better to take it to shop

Answer 4

have you checked the TPS ( throttle positioning sensor) or the fuel pressure regulator?