RPM bounce with Auto Trans

[JOPRIMO]

Hello all, I hope someone can help with this. Lately, i've had this problem, it seems to be mostly when the AC is on but here are the symptoms:

Immediately after a full stop the Auto transmission feels like it wants to lunge forward, like its engaging the lowest gear causing me to put more than the usual pressure on the brake pedal to keep the car from moving forward. After this, at a complete stop the RPM gague bounces between 500 and about 200 RPM's, like rough idle and during this the trans lunges forward each time. If i turn off the AC the problem lessens but doesn't go away. I have found that if i let the car bounce forward a bit one time then quickly press the brake pedal sometimes the problem subsides until the next stop. Sometimes i have to put the car in neutral because the bounce is so annoying, then when i put it back into Drive, it takes a few seconds to build up enough pressure to proceed smoothly without the "dropping into gear effect."

Could my tranny or torque converter be failing? Or could the idle be off a bit and the AC is exacerbatingthe problem? I'm having the TB/WP done next week so funds for additional repairs will be limited.:frown:

Thanks for any help on this.

 

[rbirling]

I don't know anything about auto NSX's, but I'll suggest the obvious -- have you checked the fluid level? That would be the first thing I'd try. :smile:

 

[JOPRIMO]

Yes, fluid level and color are good. Thanks for the reply.

 

[NSX-Racer]

Even 500 is way too low as idle rpm as I recall from my former auto-NSX. What about the idle at neutral? I bet it is steady about 800 when engine is warm, right? That leads us to the conclusion that there's nothing wrong with the idle itself (throttle body etc.) but with the tranny. I suspect the torque converter doesn't release properly. Can be a mechanical failure or (less likely) wrong oil viscosity.

Ah yes: The A/C should not drop the idle more than about 100 rpm.

 

[Jin1976]

RPM is too low. Mine is set to 800 RPM and car runs fine. BTW mine is auto.

 

[NSXTech]

Without knowing if the idle is stable ALWAYS in p or n, the following is based on a possible tranny problem only-
Your 4 spd auto actually has 5 clutch pacs. The "extra" is second hold, which keeps the tranny in second while you are stopped, and releases at the first sighn of significant throttle pressure. This keeps the strain and heat down during prolonged stops when still in D. If the tranny filter (internal, unfortunately) is very dirty, or system pressure is low for some other reason, second hold clutch will 'drop out' intermittantly, causing the car to lunge as you decribe, and also want to move more, because it may be in first instead.

This also explains why it takes longer to move away from stopped when first put into a forward gear. I would like to know what happens if you try to stay in manual 2, both stopping in that gear (from, say, 20mph) then starting out in that gear. If the problem goes away, it is definately internal tranny.
If this changes nothing, AND if the idle is always stable in p or n, then it is probabally a t/c problem.

The good news- a pressure test of all 7 pressure ports can easily diagnose this problem.
The bad news- I have overhauled many NSX autos, 2 in the last 7 weeks. Average price- 4500.00

HTH,
MB

 

[JOPRIMO]

Excellent post! The problem does not happen in either P or N and the idle recovers to about 600 rpm (500 in D). And it does not happen all the time. Today it was just fine with the AC on too. Thanks for the info and i'll try that test today and post the results.

 

[NSX-Racer]

600 rpm (500 in D).

Too low IMHO. I would let it adjust to 800.