1995 3.8L hesitation/stalling

[gelancas]

I have spent the past hour to 1.5 hours searching for an answer to my problem. I just bought a 1995 Sable GS from an individual that lived 1.5 hours away. Upon driving the car home I noticed that it would hesitate or jerk a little upon shifting into 3rd gear but once shifted into overdrive it operated smoothly. 1st and 2nd gears shift without any problem also. Well today I was driving the car and it stalled without warning while sitting at a traffic light. No check engine lights displayed. I was able to get it started right back up with no problem. I drove it back home and again noticed the jerking at around 1500 to 1800 RPMs (40-50MPH) held at constant speed. If the gas pedal was pressed it cleared up. Would an IAC valve cause this trouble? Not a very good feeling after having the car for only a day. BTW it was owned by an elderly person and only has 59K original miles. Truly a barn find, that's why I hated to pass it up. Thanks in advance for any help.

[behlinla]

My guess would be a worn TPS (throttle position sensor). Since an old person drove it, they probably kept their foot in one spot most of the time and wore out the sensor in that particular spot. So you can assume that they probably drove about 40-50 mph all the time!

The computer uses the TPS to adjust the ignition advance and transmission shifting. Worn TPS sensors spike their output at worn spots, so the computer thinks you're basically treating the gas pedal like a drum pedal and it gets confused. When you push the pedal more or less past the worn spot, it outputs normally as you've seen.

[gelancas]

Thanks behlinla! I will try that and let you know.

[pawpaw]

Originally Posted by gelancas

I have spent the past hour to 1.5 hours searching for an answer to my problem. I just bought a 1995 Sable GS from an individual that lived 1.5 hours away. Upon driving the car home I noticed that it would hesitate or jerk a little upon shifting into 3rd gear but once shifted into overdrive it operated smoothly. 1st and 2nd gears shift without any problem also. Well today I was driving the car and it stalled without warning while sitting at a traffic light. No check engine lights displayed. I was able to get it started right back up with no problem. I drove it back home and again noticed the jerking at around 1500 to 1800 RPMs (40-50MPH) held at constant speed. If the gas pedal was pressed it cleared up. Would an IAC valve cause this trouble? Not a very good feeling after having the car for only a day. BTW it was owned by an elderly person and only has 59K original miles. Truly a barn find, that's why I hated to pass it up. Thanks in advance for any help.

Welcome to TCCA.

You may have more than one problem.

I like the TPS idea, so check its resistance for a steady change from closed to wot.

The idle stall may be an acting out IAC, as its responsible for maintaining idle speed when the vehicle is put into gear, the A/C cycles on, heavy elecreical loads are applied, when the steering wheel is turned & the P/S pump applies engine load, ect. SO, you might consider removing & cleaning it with a plastic safe spray, like CRC MAF or QD cleaners, or Valvolene MAF spray & see if you get positive results. Cleaning may not last, it didn't for me on my 99 Ranger, but was a good trouble shooting step.

More thoughts for consideration, let us know how it goes.

[T_swensen]

I would see about getting the MAF sensor checked/cleaned. A bad air/fuel mixture due to a dirty Mass Air Flow sensor can definitely cause the stalling you have described.

Also, plugs/wires/distributor cap could clear it up if you don't find anything else. (A spark plug service is always recommended when purchasing an older car that may not have ever seen new plugs.)

[gelancas]

Thanks PAWPAW and T Swensen!

I went ahead and replaced the TPS since the vehicle is so old, and it appeared that the part was original. However, it didn't fix the problem. I will try cleaning both the IAC and the MAF as prescribed and let you know.

It appears to have new plug wires and a new distributor cap, so I'm guessing the spark plugs have also been changed.

Thanks again for all your input.

[sfhess]

Originally Posted by gelancas

It appears to have new plug wires and a new distributor cap, so I'm guessing the spark plugs have also been changed.

Maybe. Maybe not. They are difficult to access so they may have been left alone. I wouldn't assume anything.

I changed front plugs on my 3.8 a few years ago but left the rear bank alone because I couldn't get the boots off. Plugs were changed when I had the heads off to replace the infamous 3.8 head gaskets.

[T_swensen]

Originally Posted by gelancas

Thanks PAWPAW and T Swensen!

I went ahead and replaced the TPS since the vehicle is so old, and it appeared that the part was original. However, it didn't fix the problem. I will try cleaning both the IAC and the MAF as prescribed and let you know.

Make sure you use the special MAF sensor cleaner so that you don't destroy it. Using carb or brake cleaner is not a winner in this situation.

[T_swensen]

Originally Posted by sfhess

I changed front plugs on my 3.8 a few years ago but left the rear bank alone because I couldn't get the boots off. Plugs were changed when I had the heads off to replace the infamous 3.8 head gaskets.

Seriously, getting those plugs replaced is much easier when the head is sitting on a bench!

That was probably the only fun part of the head gasket job I did on my brother's '95 Taurus sedan.

[sfhess]

Originally Posted by T_swensen

Seriously, getting those plugs replaced is much easier when the head is sitting on a bench!

That was probably the only fun part of the head gasket job I did on my brother's '95 Taurus sedan.

Front plugs not exactly a picnic either. Working on a 3.8 is like working on a 390 in a Mustang.