'99 Transmission shift trouble + coolant issue

Got a '99 with 65k on it, and just recently I noticed that sometimes, when holding the throttle steady, the engine will surge ever so slightly (<100rpm) as if the transmission is trying to upshift to go up a hill..usually its level ground or a very slight grade. At first I thought it was cruise control, because that's when I first noticed it at 75mph. Now it'll hit around 1500rpm no matter the speed. If I give it just the slightest variation in throttle it'll either slack off or shift up, depending which direction my foot chooses to go. Think its some wacky sensor deal in the engine, or is my tranny packing its bags to go south?


Unrelated note, I'm about a quarter inch low on coolant every oil change or two. There's no leak in the system (at least the perimeter) and I'm sure by now the infamous gaskets are trying to go on me. I don't smell funky exhaust and I don't see anything out of the ordinary in my oil. Got an opinion on this?

I think you might want ot disable that TCC mechanism, and see if it is jumping in and out of lockup, and that's what you are feeling. The conditions you describe when it happens sound about right for lock up realease threshold.

Your mileage is about right for the water pump to begin seeping a little. Stuff a paper towel up behind the bottom of the water pump pulley after you drive it, and see what's on it after it sits all night. Bet you get some wetness. Dont forget to take it out.

On your coolant leak, if your car is a 3800, you probably have the cracked intake plenum that plagues every 96-00 3800 sooner or later. If its a 3100, it's either a leaky water pump like Jeffco said (although normally you will see coolant leaking), or the infamous lower intake gasket leak that every 96-up 3100, 3400 will experience at least once in it's life.

I'd change the fuel filter and see if that makes any difference with the tranny

I changed the filter about 3k miles ago, but I noticed my fuel pressure (with my overly expensive NAPA fuel pressure guage) is just a hair under 40 at engine off-key on. Haynes says I need close to fifty psi...unrelated note, according to my gas guage I have horrible mileage (less than 16mpg hwy)..but I can drive an extra 60 miles or more after I hit E. I know the pump and float are a single unit, but my question is would a drop in pressure such as this cause the surging? It drives normally everywhere else, and she's got plenty of pickup without missing.

I thought it was 37 psi or something like that. 3.1? Baffle in tank laying on pickup/float? Do it worse near full or empty?

you try unplugging the TCC?

It might be a little harder to disconnect the TCC on a 99 with the 4T60E tranny, I am fairly sure they are like the 4L60E with one main electrical connector with something like 12 wires going to it

Pull the fuse for it.

I'll try the TCC suggestion tomorrow when I get out and about, and it don't change any at full or empty.

Couldn't seem to get to any kinda fuse or plug for the thing, mine's the single fat connector. Any idea what wire to yank? Or is there some fuse I overlooked?

edit for Jeff: I looked up the Haynes stuff again, the PSI varied by year for some reason. 97 has about 31psi while 99 has close to SIXTY (!) psi on key on - engine off.

97 engine off: 47max; engine on: 44max
99: 52min/59 max regardless

I'm not too sure what the GM folks were smoking but the figures for all four years is kinda wavey. Up then down then up then down then up again. Crazy.

If you have any hard starting problems, I'd be checking out the fuel pressure regulator.

Nope, she'll start up in a split second. I barely have to turn the key before it cranks, much to my happiness.

I guess they don't want us playing with their TCC's anymore. I looked at mine, and don't see how to do it either. My fuse reference in the owner's manual shows the TCC among other things on one fuse.

A very wild guess, but it seems that a bad spot in the TPS might cause the tranny some confusion.

there's two valves in the valve body that have wear problems,,,,,,
one fails and you loose O/D The other fails and converter un-locks,,
You will have to check when it falls out of gear to see which problem
it has ,,,,A good tranny shop can replace the valves ,, Sonnax valves
are recommended