Slow Idle - Tranny Question

[Zilverado]

Can a low idle (around 400 to 450 rpm – specified normal is 750) condition cause an automatic transmission to temporarily disengage or “slip”?

The engine runs so slow that the vehicle will barely move or not move at all when sitting at a light and foot off the break. Sometimes when shifting the tranny into reverse, it won’t kick into gear until I bring the RPM up, and then it kinda “slams” in. I’ve had the tranny rebuilt before for a similar type of problem (but no idle problem at the time), so I’m just a little nervous now. Or could the slow idle be causing this?

FYI, the engine in question is computer controlled, fuel injected (not my Chevy), and so the idle adjustment is not just a simple turn of the screw.

Any suggestions would be greatly appreciated.

Thanks

[86k10]

Slow idle will cause the not moving while sitting still with your foot off the brake, and yes is it's slow enough it can come out of gear, but I don't think 450 RPM should do it. You could have the beginning of pump troubles or a leaking forward clutch drum, or something in that circuit. What kind of trans are we talking about?

[Zilverado]

Thanks for the response.

The trans is on my wife's '92 Pathfinder - a 3 speed (+OD) automatic. We had the reverse circuit rebuilt about 3 years ago - at less than 100,000 miles (at a cost of $2,500 Canadian ) We now have almost 150,000 miles, and would hate to have to spend that kind of money again.

I will be getting the idle looked at in the next little while, and hopefully the problem goes away. If not, I'm starting to think the Pathfinder should go away...

[86k10]

I was afraid you were going to say it was a foreign job. But in reality they all work with kind of the same principles. There is one good way to tell, but you will have to get some figures from a trans manual. If there are pressure taps to do it with, you need to check line presure and at the same time check what ever the other ports are whether reverse or 2nd or any other gears, to check for a leak in that particular circuit. But I would at least check line pressure at 450 and then 750 and compare them, that will at least show you if slow idle affects pressure. But make sure you have it warmed up to operating temp before you do this, for the most accurate readings.