Help! Automatic transmission shifting problem

[JR Purser]

My 93 240sx convertible automatic has started shifting at high RPMs (all gears) and when I let off the gas, the rpms drop almost back to idle (not staying fully engaged) except in 4th gear (stays engaged). If I manually drop it into 1 st or 2nd, the engine stays engaged to the transmission. I've flushed the transmission but it had no effect on getting the trans to shift at normal RPMs/speed. In order to get it to shift up to the next higer gear I have to get the RPMs/speed past 4000 rpm and let off the gas. I tried the self diagnostic transmission procedure (posted by wiwalsh) but I get no flashes after step 15 on the OD Lamp I'm thinking TCU problem..any suggestions?

[tonynalli]

try using something called transmedic. or something like that. you will find it in your pap boys or store like that. it will be near the fuel and the oil additives. put the whole bottle in the transmission. it might be your seals that are bad. the transmedic will soften them up and allow them to hold properly. its only like 5 bucks a bottle. i belive lucas oil makes it also. its what i used in my old auto.

[JR Purser]

Thx Toni...but I already put a high quality ($15) seal conditioner when I flushed the transmission and it had no effect. I checked the ECU and I get a code 55 from the single red flashing LED (normal). Right now I'm checking out the Throttle sensor, Revolution sensor, speed sensor , Inhibitor switch and lastly the TCU. I tried getting the TCU out but its way up in the right footwell and I'm trying to figure out how the hell to remove it without taking the whole dash out..UUUUGH! It's very tight in there to say the least. Any Ideas? I disconnected all 3 connectors in the engine compartment (on the left side of the main fuse/relay box) and the transmission shifts at normal speed in drive 2nd to 3rd (except it won't start in 1st gear even when I manually put it in 1st). Didn't have enough road to see if it would make it to 4th. However still does not stay engaged in drive when I let off the throttle. So back to diagnotic mode. Appreciate any more HELP!

[tonynalli]

next time i go home i will look at my fsm to find the locations for you. oh and by the way the name it TONY.

[JR Purser]

Thanks TONY....checked out the TPS with a digital Ohm meter and I get 5k-13K ohms... idle to wide open.. may as well clean the throttle body while i'm in there. I'm Going to replace the Throttle Position Sensor today and see if that helps. Initial transmission sensor checks through the 3 harness connectors in the engine compartment check out ok except for the fluid temperature sensor which i get no reading..wide open. FSM says it should read 2.5k - .3k ohms cold to hot But i doubt that would cause this problem? Sure would be nice to hear from someone who had the same problem and how they fixed it..short of replacing the whole transmission!

[tonynalli]

do you want to buy a tps from me. ??? i have like two of them...email me at [email protected]

[yellow_jacket]

If the tps was bad you would also have a run condition. Have you checked all the fuses? Are all your harnesses running down to the transmission good? This sounds more like a hydraulics problem. If it was electrical the transmission would shift at higher points, but the revs would stay up when you let off the gas.

[JR Purser]

Tonynalli...Thx Tony but I just ordered 1 from Advance Auto..$45..no one had it in stock in the Clearwater Tampa Bay area..gonna pick it up today.

yellow_jacket...Thx for input..checked all fuses first..all OK under hood and left kick panel. Harnesses ck out ok too. Disconnected the TPS and Idle/full throttle plugs from the TPS unit and the transmission shifts at normal/low RPM/speed and stays engaged..so it must be the TPS..go figure! Replacing TPS today..will let u guys know result.

[bbovee]

JR...an oddity that we've both discovered and embraced the forum as a viable source of info within the same time frame, live in the same area, and have the exact same problem with duplicate cars.I'll be following the responses closely but would also appreciate contact from you with the grand finale of diagnosis and resolve.I have someone who can help me with fixing it but would like to have more info prior to the endeavor.GOOD LUCK! [email protected]

[JR Purser]

bbovee...Ok got a TPS $45, pulled the throttle body and while still off the car (easier to adjust),set the idle resistance to 1k (rotate sensor on the 2 screws that attach the unit to the throttle body) and made sure the idle switch was making contact at idle and the full throttle contact closed near the wide open position. (may as well clean throttle body while you've got it apart with carb spray or even better throttle body cleaner). Get a throttle body gasket also while you're ordering)

Put it back together and WaaLaaaa..... engine shifts smoothly and perfectly in all 4 gears. Obviously if the the TPS is not within specs or malfunctioning, you'll get this problem and probably more..definitly a critical/main sensor for the transmission.. GIve me a call (727-462-9774) if you need further info...be glad to help![

[bbovee]

JR: Thank you soooo much for the input. I've tried to call you and left a message on your answer service. DO get back to me because, as a result of my homework on this site I've discovered other valuable info that can do nothing less than make your car run better...even after your TPS resolve.I've also discovered a parts site (through the gracious share of another club member) that will be very advantageous throughout the ownership of your car...we'll, probably, end-up competing for parts?!Get back to me, 'B'

[bbovee]

I'M PSYCHED!!! JR, your advise was outstanding! Your response (TPS and gasket) to my dilemma resulted in The Perfect Solution! Found the TPS ($32.49) and gasket ($1.49) at NAPA. The first NAPA I called didn't have the parts in stock so they did a computer search of their inter-store inventory and located both parts in St. Pete...saved me a lot of phone calls and galavanting.Surprisingly, the removal of the old parts and installation of the new didn't take long and now......MY CAR IS PURRING!!!I can't thank you enough for sharing your solution!:ylsuper !!!

[JR Purser]

Purrrrrrrrrrrrfect...glad to be of help in keeping a rare classic convertible on the highway. Hope to see you on the streets!

[SHIFTrl240]

shoulda just done a auto to manual swap