Surging

[Buick Granny]

95 Buick Regal Gransport 3.8 Surging when maintaining same speed (not drastic but enough to drive you crazy) does not effect the power.
Some times stalls (3 times in 2 months) with no indication when stopping at the top of an exit ramp, Tack just keeps dropping all the way to zero, no indication until you loose power steering.
Signs point towards TCC, except when it stalls I drop it in neutral and it starts right back up. Replaced previously 3 coil packs, plugs & wires, Alternator, Vacuum lines, Fuel Filter.
Also shakes (sounds like a helicopter) when I apply the breaks coming off the Hwy. Replaced All break pads and front rotors. That maybe a tire rotation issue, does not pull left or right. Will rotate and see if that takes away the shake and then would reduce the possibility of the TCC?? ANy help or diagnostics would be greatly appreciated. Also no check engine light comes on!!

[Buick Granny]

oops 141k, Tack does not move with the surge

[Venturi]

Hi welcome to the site.

Next time you’re on a smooth level road and notice the surging hold the throttle steady and lightly apply the brake (not enough to actually apply the brakes but enough to actuate the brake switches), see if the surging disappears. I’ve seen a number of these with torque converter shutter which will cause a surge at steady speed. Tripping the brake switch will unlock the TCC and the surge should disappear if it’s being caused by torque converter shutter. Tripping the brake switch will also disable the EGR flow. Excessive EGR flow can cause the same problem but due to the design and control of this type of EGR valve it’s rare to see that on this engine.

The stalling is a hard one, there are a lot of possibilities here especially since it seems to be so intermittent. When you restart in neutral after the stall does the engine stall again when put into gear or can you go on like nothing happened?

Is the brake noise accompanied by any pulsation in the brake pedal or shake in the steering wheel?

[Granny]

Starts back up like nothing ever happened..very strange. As for brake noise, nothing coming from the brakes themselves. Its more like a loose lug nut kinda shake, and sounds like a helicopter. Replaced all lug nuts as well, they kept stripping. Probably had the wrong ones to begin with.

Will try tripping the brake switch. Thanks

[Granny]

Let me define "Surge" it's not an excelleration surge, more like a light tapping of the brakes while maintaining the same speed.

[Venturi]

Ok, try the brake switch test and we'll go from there.

[Granny]

Tried tripping the break switch and it seemed to temporarily work (about 5 minutes max). So temporarily, If asked to answer yes or no, I would have to say No. Could have been more wishful thinking. 28 miles of hwy driving, tapped about 12 times?? I think people thought their was a cop around somewhere with all the tapping. HA

[Venturi]

Tapping the brake will only disengage the TCC as long as the brake switch is tripped, as soon as you release the pedal everything will go back to normal and the TCC will go back into lock-up if the vehicle speed is high enough. If the surging stopped while the brake was applied you probably have an issue with the torque converter clutch.

Yea, sometimes the things we have to do during a test drive can cause you get strange looks and gestures from other motorists.

[Granny]

Thanks for all your Help. It seems that it really starts as soon as the car shifts into 3rd gear around 40mph. If your maintaining speed and it shifts, your only option is speed up or slow down! Does that fit your thoughts?? I also read some where that if you temporarily unplug the TCC and if the problem stops, the TCC is your problem. The auto repair rookie that I am cant find the appropriate plug location to try it. Would you recommend trying that?

[Venturi]

If I remember correctly the TCC and the shift solenoid wiring may be all grouped in one large connector so I don’t think you can just disconnect the TCC. Do you know which transmission you have? I think it should be a 4T60-E but I’m not sure.

Out of curiosity what kind of shape are the basic tune-up items in? Sometimes a plug or plug wire breaking down can make the car feel like its surging rather than misfiring too.

[Granny]

hmmm.. General Tune up items. Plugs and wires 6 months, air filter 1 month, fuel filter 1 month.

Also, rotated the tires back and found a rear rotor out of round and a flat spot on the Lugs. Replaced rotor and lugs. Runs great and no more helicopter!!

I payed closer attention when driving the other night and kept my foot slightly on the break for a few seconds and the tach would go up and the surging would stop. Does this confirm your thoughts?

[Venturi]

I’m glad you got rid of the helicopter.

It sounds like either the torque converter or the TCC may be causing the surge, unfortunately the only way to verify this is with a scan tool. The transmission can be monitored on the scan tool as well as other engine control data such as fuel trims. It’s important to verify that all the engine control parameters are in range before pointing the finger at the transmission because an underlying condition can be more pronounced when the transmission goes into overdrive.

I think you’re going to have to take the car in to a full service repair shop that can actually test drive the car while monitoring the engine and transmission control data in order to diagnose the problem.
I wish I could do more to help pinpoint the trouble but unfortunately without actually being able to put hands on the car I can’t make an accurate diagnosis.
I am interested in finding out what the problem is so please keep us updated. We’d also be happy to help with any other questions you may have.

[Granny]

Ummmm.... I only have one flat spot in my driveway and their always seems to be another vehicle parked there. (bet you can tell where i'm going with this) Moved the other vehicle and checked the Transmission fluid on perfectly level ground. It's amazing what an impact a Quart of fluid will mess up huh!! Runs pretty good now! Don't revoke my Mechanic learners permit!! ;D

[Venturi]

Ha, I thought about asking if the trans level had been checked when I asked about the tune-up items but I assumed it had been checked. Sorry…. I shouldn’t have made that assumption.

Can you locate a fluid leak? The trans pan and the lines to the cooler in the radiator are the most common sources of leaks.

[Granny]

I had checked it..but only for signs of fluid due to parking on inclines. Will have to look around and clean up under the car to see where the leak is coming from. Will let you know what I find. Thanks again.