Engine bogs after accel w/ clutch in & trans in any gear onl

Hello everyone. I' m new to this forum so excuse me if I'm inquiring in the wrong place. Anyways I just bought a 1992 b2600i from an older fella. Pretty clean truck with low miles but having an issue with the idle when the clutch engaged and in gear (any gear). As I rev it and allow the idle to drop with foot off the pedal the engine boggs like it is going to turn off and then corrects itself. On the other hand with clutch engaged and not in gear, it does fine and even without the clutch engaged. Is there a load sensor or transmission sensor of some sort? Anyone please advise. Thanks

I responded to your question over in the post about performance parts for the b2600i

Yes thanks crazy. I took the truck to a mazda service dealer and they said its the bypass valve. That unit runs approx $650. Too much for something that small that goes attached to the throttle body.. I'll see about picking it up at a dismantling yard or something. If I get lucky.

Post a photo of this part that shows its location as I'm not familiar with B2600i engines, just the B2200. There's a B2600i (1991) at the parts yard I visit, going there in a few weeks. I saw this truck yesterday, the engine was still mostly complete.

Look in manual posted in the b2600 manual thread, page F2-142 BAC valve. Connected to the throttle body on the 2600i FI.

Check your yards. But my experience is that these tend to go out with the engine if your local yard frequently pulls engines. If you do find one, make sure it's not a 89 and that it looks just like yours. The 89 model had one that bolts on the back side of the throttle, where as the later years bolted on top like yours.

They are typically available on eBay for $70-$100.

Also, if you are looking for it online, Mazda calls it Bypass Air Control (BAC), but the rest of the world seems to call it an Idle Air Control Valve, or IAC. You'll probably find it a little quicker searching that way.

Thanks for all the good info guys! I'll be sure to keep an out for it at a couple of dismantling yards in my area and also online ie eBay.

To answer your original question, there is a sensor on the transmission that tells the engine computer it is in gear. I will assume your B2600 is pretty simmilar to my B2200i, mine bumps the engine idle by 200RPM or so when I put it in any gear with the clutch pedal pushed in. Must be some sort of anti stall system.

I had my tailshaft out of my truck when I rebuilt the motor, and there is a switch on the shift shaft right by the shifter, it pushes in the switch when it is not in neutral.

Found one on eBay for $90 bucks. (thanks for the advise "91 2600i"). Installed it and it does the same thing. Incorrect diagnosis by the Mazda dealer. It looks like to me they don't even know the cause of this. They had to call Mazda themselves and still same problem. Lost faith in them. Anyways, my next option is to look into this switch on the tranny like "befarrer" has stated. And yes it does exactly as you stated but with but with a low idle (almost turns off) after a quick accellaration and then corrects itself. I hope its not the computer and more like that sensor or something else in between the sensor and computer/IAC valve. I'm still open for any advise. I have to say, this blog/forum is pretty cool. Very helpful tips and info by good people. Thanks guys.