97 Malibu hesitates at cruising speed

[97malibublue]

I have a 97 Malibu 3.1 which I received with a intake problem.So I recently replaced intake gaskets. It had been setting for a few months. The car seems to run fine except for when you reach cruising speeds especially going up hills. It will start to hesitate or stutter, not sure how to describe. The rpms will drop 3 or 5 hundred for just a split second. This will do this repeatedly as long as you are continuing at the same speed. If you accelerate it stops. I have changed plugs and wires. This did not help. No CEL light either. Does anyone have any ideas? Thought about fuel problems but it would seem to do it more often if it were fuel related. Thank You

[rodeo02]

That's a tough one w/out any CEL or stored codes (random misfire, etc..) I'd guess at contaminated fuel, a failing fuel pump, a clogged fuel filter or maybe a catalytic converter that's getting plugged. That cat thing would eventually set a catalyst system inefficiency code though. I've seen fuel pump problems not set any code.

Joel

[stratford_boy]

What speeds is this happening at? Could it be the torque converter is locking up and unlocking? If this is the case, then it might be normal.

[97malibublue]

It usually happens between 55 and 65. I thought it might be the transmission slipping so I tried driving with the shifter in third gear and it did the same thing. We had a MPV Van that had some overdrive trouble once and it acted about the same. I know this car has no overdrive but I am willing to try anything. Would fuel related issues only happen at certain speeds or conditions?

[stratford_boy]

No, not usually, fuel issues would be under all kinds of driving conditions. Not just at a specific speed and load.

[97malibublue]

Yesterday it started doing it at slower speeds. It seems to do it when you keep the accelerator in one position.

[stratford_boy]

In exactly the same position every time?? If so, very uncommon, but might be a throttle position sensor...

[97malibublue]

Not sure if it is the same position. I just notice when you keep it at a steady speed it is more noticable.

[stratford_boy]

Had a malibu in the shop a couple of weeks ago with same type of issues, try this first. (Cheap things that need to be done on a regular basis anyways.) Using a can of air intake cleaner and an old toothbrush, clean the throttle plates. Remove the IAC motor and clean the pintle and spring, as well as the passage inside the throttle body. Also get a can of mass airflow cleaner and clean the mass airflow sensor. (spray the mass airflow sensor only, do not touch..) I do this to my car once a year. Make sure everything is spottless. Clean the throttle plates while holding the throttle open. Post back with your results...

[97malibublue]

I know about the MAF sensor. But I am not familiar with the IAC motor or pintle and spring. Can you give a little detail or picture where it is located? Thank You

[bcopeland]

I had the exact same problem. I thought it was the ignition coils, the spark plugs an wires, etc. Finally, I was convinced it was the fuel pump. I told my machanic and he tried to convince me that I was wrong but I had him replace it anyway. Problem solved. I bought a fuel pump rebuild kit from Ebay for about $50 rather than a $200 fuel pump.

[97malibublue]

Thank You bcopeland. I will look into the fuel pump issue.

[RAM_MAN]

2000 Malibu hesitates or stumbles at cruising speed, 55 - 60 mph. If I accelerate or decelerate the stumble disappears. There is no DTC code or service light on. The spark plug and wire are relative new; new fuel filter. The throttle body recently clean.

What cause the problem? Is it the fuel pump?

Any suggestion will be appreciated.

Thank you

Ram_Man