Bucking/Backfire problem. Even read Archives!! Help.

[FauxZ]

Howdy,

First off I'd like to say thanks for providing such insight and support via
your web sites.  I'm also a member of SOGI (Supra Owners Group Int.) and
se-r.net blows our main site away.  Bravo.

Now down to the issue.  I've been trying to get my girlfriends 93' G20 up to
snuff.  The car was obviously neglected in a previous life and a victim of
poor choices in maintenance.  I know the SR is a great motor and I'd like to
get this one back to it's former glory.  The problem is that the car seems
to have a severe backfire once warm.  Engine speed does not matter though
it's much less noticeable as RPM's rise.  At high load, low RPM it's often
so bad as to sound like someone set off a firecracker in the airbox...  I've
started at the cheap end of the repair spectrum and have worked my way up to
where I'd like some second opinions before I start spending some serious
money.

What I've done.  I've cleaned the EGR valve as well as the little pipe off
the "other valve"..  I've also tried just disconnecting the EGR...  I've
felt the EGR while revving the car and it appears to operate smoothly
without any jerking...  We'd done the full "tune up" routine...  Plugs,
wires, cap, rotor and new O2 sensor.  All this was a bust...   I checked the
timing last night and found it past the 20 mark (did I mention bad
mechanics?)... It's back down around 15 for the time being, and this has
seemed to help, but not eliminate the problem..  I might have a problem with
the PAIR Valve leaking under some throttle conditions but I'll have to check
again after reading that it opens up on Decel..

The "bucking" is much more pronounced than a simple miss... At 15mph and 2k
rpm it will rock your head forward (like fuel cut on a supra if that
helps)...I plan to check the MAF when I get my Multi-Meter back, but I can't
seem to think of anything else except cleaning the Injectors...  I would
like some opinions before I start sending injectors off to RC as they only
have 120k miles on them and $100 is a bit beyond my "guess" limit...

Thanks in advance for any assistance,

Zaron <----- 93 G20, 91 Supra, 85 Supra.  Phoenix AZ.