alright so as the title says i bought a 91' cavalier z24 for about $950. 3.1L 3spd auto. Its got roughly 166k on it and runs drives great the only issue is that when your slowing down as you get to say 15mph it acts like the transmission is just now downshifting and as it shifts (or whatever its really doing) the rpms rise on there own which puts power to the wheels... needless to say not the best thing when your trying to stop... what could be causing that? And besides this issue, what are any other things that would cause problems in the forseeable future? the previous owner changed plugs and wires (they look pretty new) and he also mentioned replacing a sensor and replacing the ecu/pcm all within the last 2 months.
Also what would help gas mileage... cold air/exhaust/tune? Is the computer in these cars tuneable or do they have a chip that you can change the tune on or hows that work?
94' Camaro z28 a4= bolt-ons and cam
91' Cavalier z24 a3= stock DD
As for your issue it could be the be the TCC switch torque convertor solenoid is going bad.This affects the trans shifting and causes several issues,like what you stated and also cutting off coming to a stop or going from park to reverse.You can unplug it and if it goes away you will need to buy a new switch (advance auto parts) and drain your trans and do a filter change too(I think these have filters?) but NEW fluid is a must before installing a new switch.In short the fluids additives to protect from temps,and lubricating wear out and burn up the switch causing all the drama.I am not sure if it is a two plug terminal or four but on top on trans on memory(tired after drvg 520 miles) so bare with me.Unless your other electrical items like a map sensor(maybe but) this would be present at idle not just slowing down,maybe a tps or egr valve is gummed up or loosing vacumm.Start with the TCC switch.I am way too tired to search the part tonight on the auto site for parts.But it may be listed in trans parts or sensors cannot recall when i last looked it up for some one else and linked it.
The ECM you have is OBD1. It does have a removeable chip, but you aren't going to find anything aftermarket to replace it. Unless you have some sort of modifications other than simple bolt ons, you aren't going to need one either. There are several guys on V6Z24.com that make custom chips if you're interested.