1995 W124 Wagon - Surge Issue
 

Hi folks,

From stop, slowly accelerating, the wagon RPMs suddenly surges when it reaches 2K-2.5K RPM marks when cold or warm. When the car gets hot, I have no surging issues even starting from a stop position. Any ideas what maybe causing this surge? Could it be a transmission shifting issue? Any assistance is greatly appreciated. Thanks!

Does the vehicle change speed with the surge in engine RPM? If not, the transmission is slipping.

The wagon still accelerates in a constant pace when it surges. Could it be the modulator valve?

The modulator affects shifting firmness. Slipping while in gear is due to wear, problems in the valve body, incorrect fluid level or type, or a worn pump causing low operating pressure.

Check the fluid level before getting carried away. If it's been >30K miles since the last transmission oil and filter change, the time is well past and could be a contributing factor.

I'll check tomorrow morning. There are some leaks on the ground and after close examination it looks like ATF, red in color.

Have the throttle actuator and upper harness been changed out with post 1998 replacements? When were the coils and plugs last changed?

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Those issues should be addressed, but they're not the problem here. If they were, the car would be lurching forward as if under firm acceleration when the engine RPM spikes.

Good luck

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I tried measuring the transmission fluid using this procedure:

Started the car
Warm up for 20 minutes
Shifted the car through its gears
Pulled out the dipstick and wipe off using a lint free rag
Push back for 5 seconds
Pulled out to measure and I could not tell if there was any fluid being measured.

I did this many times and still cannot tell for sure. Now, when the car was cold this morning, I pulled out the dipstick and there was fluid in the dipstick. Is there something I should be doing? Is there another procedure I need to know to properly measure?

Transmission fluid will "fill" into the pan as the unit cools. The primary reason for "fully warmed", running in park on a flat surface. Drive the car for 20+ minutes, a couple of traffic lights etc to get it warmed up.

You'll notice a series of small notches on the bottom of the stick. Look for fluid to be in one of them. Best if it was in the middle.

Jayare

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Got it! The ATF fluid was low and once filled, the surging stopped. Whew!

However, There is a prominent leak coming from the modulator valve. I ordered a replacement part and should be arriving today so I can work on it this weekend.

From what I gathered, this is a remove and replace procedure and fine tuning involved if need be. Before removing the part, do I have to drain the fluid? Thanks.

Hi, neighbor! are you the owner of a smoked silver 95 wagon like mine parked occasionally near W 3rd ave? I guess we should meet up sometime.

You don't have any problem removing the modulator valve as its above the pan.
FWIW I just sent my '95 wagon to have its tranny rebuilt, it started shifting oddly, hard clunks as it nears a stop then started slipping under power. And the rear main seal leaking so need to pull the trans to get to the back end of the motor so may as well.
The consensus of the folks at MZF aka Peter Schmid transmission shop in Burlingame was it is due a rebuild (not doing the work there however). Oh dear, its going to cost me more than I paid for the entire car 3 years ago, at only 150K miles its sad to have to invest in a transmission job but I drive the car a lot and its in good condition....
I hope yours is not in the same category..
DDH

Thank you for the info. The modulator has been replaced and the rubber gasket is very brittle and just replaced the whole unit.

Unfortunately, I have one more leak coming from the same area. The leak is coming from harness that is plugged into the transmission to the left of the modulator.

Does anyone know hot remedy this problem?

Dieseldiehard - when you get a chance, PM me and like to meet peeps with the same wagon.