Need some advise. Initially after installing a secondhand auto transaxle, the car drove smoothly for its firstshort trip. Since then, its been running like s***. Starts easily, idles OK with perhaps the occasional subtle miss. Initially it would die without stalling if I opened the throttle quickly, and run terrible till I coul coax it up to highway spee, sitting on 100kph it woul purr till I slowe own or stoppe then the thing woul run awful again, almost as if it wasnt ajusting the timing as I change throttle position.

Have put new plugs in, new fuel filter, blown out the thottle boy thoroughly, an now its worse, cant even get it to run smooth at highway speed. But now it at least has generated a code, which relates to the mass airflow sensor. Wondering if this is a common problem, does it need cleaning, or replacement, or are there other things to check first. Or is this usually a sign that the ecu is on the way out?

Seeing you replaced the gearbox the problem is likely to be something you removed/replaced during the process. Check the MAF wiring and clean the plug, TPS plug etc, anything that was electrically disconnected and reconnected during the trannie transplant. Also check the air ducting for leaks at the joints, splits in the duct etc. Sounds like it is running very lean, I wouldn't be running it at any speed while it has the problem. Pull a plug to see if it is really running lean. When you cleaned out the throttle body and made it worse, my thinking is the air leak or electrical problem is in that area, ie between the MAF and intake plenum.

Thanks MadMax, will check all that, maybe the plenum chamber as I removed that to change the plugs before the check engine light started to show up. Wondering can the exhaust cause this, through a leak or other issue? The air ducting connections are done up tight, might put some sealant at the joints just to make sure theres no leaks there, cant see any holes or damage. Only connections I havent rechecked are the various connections to the transmission, so will give all those a good cleaning out, althought the box came with all the old plugs in situ, to keep them clean.

Wondering if its worth hooking up an MAF off someone elses magna to see if the trouble goes away, but am a bit reluctant in case I have a short that could stuff their component.

Anyway will check out things given your advise, if I cant rectify it, then its something more complex and beyond my ability, so will then have to take it to someone with a scanner, only two of them in town.
Another thing Ive noticed is whist giving the throttle body another cleaning, and revving the motor, noticed the check engine light does intermittently go off whilst opening the throttle, but only momentarily, which oes sound like its sucking air somewhere I guess.

Went back over everything, no vacuum or exhaust leaks, starts and idles OK, oesnt stall at idle, check engine light comes on even after disconneting the battery. Diagnostic code 12, initially thought it was coe 21 as it looked like it flashed in that order, but then realised that there is one long flash followed by two short flashes, then it repeats. Time to take it to the professionals.

Manage to get a good MAF sensor unit from the wreckers, disconnected the battery during the install, and ran it at idle for 10mins, now there are no check engine lights, and its running much better. Took it for a drive down the highway a couple of kms, evrything went reasonably good excpt aftr pulling over, and trying to accelerate normally, it wouldnt gt up and go like it use to once, but moved off OK with more gentle throttle increase then everything was fine.

The car sounds like it has an exhaust leak somewhere, so I think that could be one reason why it isnt back to perfect tuning. So parking her up for now, dont want to risk doing any damage till I can get it looked over and scanned for any problems that arent presently showing up.

Anyway, hope the story of this may help others having acceleration/ power problems. Not sure if my MAF was dodgy before showing any codes, but I have heard that this important sensor accounts for the largest percentage of the engine management role of all the sensors, backed up by info from the other sensors, so I guess if its stuffed, the tuning becomes quite stuffed up as well.