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Decided to take the mx out for a drive today..It was fine most of the day until I was coming home and I stopped at a light..All of the sudden the rpms dropped and then came back up...dropped and came back up. I looked thru all the threads about this and found that some had vaccuum problems and others believed it to be voltage. I have zero air leaks and I had just put my battery back in my car from charging it today. HELLPPP!!!

I have a v6 so I don't know if it applies but mine does that sometimes once the engine has been warmed up for awhile and I have it in gear just idling with the clutch in.

Same **** happens here i love stick

i got a bigger engine ground and that seemed to help some, but didnt fix it. the S-AFC worked the best(i idle @ +7 or 8 correction).
one time the damned flapper door got hung wide open(yeah, that sucked) but uve got the other(DOHC) MAF so i dont know...

I had 95RS and I had the same or similar problem. On the day I got that problem, I was at casino having buffet that was like 20 miles away from my apartment, and when I got on the car after the meal, things started. Was it like you can drive it, but you can't drive fast, and the car does not go as much as you hit gas pedal? Mine did not die, but barely survived on that day and drove back home on interstate since the casino was over the river and I needed to take interstate.<p>Basically, I took my car to mazda and took them about a week to figure out. The diagnosis cost me about $100 (us). First, they thought it's distributer, but it wasn't. After all the hassle, I believe they changed alternater, and it's back on track. The good thing about dealership was they don't charge me whatever I don't need. Diagnosis is one time charge at about $100. Some bodyshop charge us what they do (some bodyshop in my neighborhood wants $60 per hour for diagnosis).<p>I hope my advise would help you.<p>bungo

I'll see the friend this weekend (I sold my mx to her) and make sure if it really was alternater or not. Also, I'll check the price of it and the labor.<p>bungo

Oh my god lets fix this once and for all.<p>It's not your alt., distro, head gasket, battery, O2 sensor or cat.<p>IT"S THE AIR BYPASS VALVE!!!!!!!<p>Location<p>It's located underneith your throttle body. It has two hoses going to it one from the air intake and one I don't know. <p>What it does<p>The air by-pass valve compansates for when you let off the throttle fast the plate in the throttle body kills all the air going into your engine. Your engine need some air to run. The air bypass valve opens to let you car idle.<p>What to do:<p>Stop your engine.<p>located air by-pass valve.<p>unplug electrical connector<p>start car and drive for awhile.<p>The car will idle at 1,100rpm or so. Normally it would be at 800-900 rpms.<p>If your problem goes away, your air bypass is bad, clogged, dirty, hoses missing or something. <p>Buy a new one for $200+ (or leave it unplugged)<p>I've been driving my car with it unplugged for about 1 year and passed oregon emissions test with it unplugged. <p>If you doubt this little do dad does anything unplug it. Start your car, and plug it in while the engine is running. Your engine will stop.<p>Info based on a 1993 1.6L SOHC w/manual tranny.

Hey check the throttle positioning sensor on the back of the throttle body. Mine is doing the same thing and it is the TPS. I cant find one anywhere dealer wants 300.00

It's not the TPS sensor. Those rarely go bad. Befor you go changing the TPS sensor anyway have you checked it with an ohm meter?

Rarely is not never.

It sounds like the same problem I had with my protege. It was the water thermo switch. this caused the car to idle up and down, stall out a couple of times and make the car run rich or lean depending on how the switch goes bad. This switch is part of the "choke system" for the car. It is one of the sensors that tell the computer that the engine is cold or warmed up. The check engine light didn't even come on so the guys at mazda thought I was crazy because it wouldn't act up for them and they couldn't get a code from the car, but I lucked out because there was another car around here that had the same problem and its engine light was on and they got a code for this switch and it fixed both of our cars. It only cost me $46 CND to fix so you can try this if you want, I hope this helps.<p>P.S. I am sorry for the long post.

Can someone take a picture of the air bypass? PLEASE!

Check out page F1-108 of the online shop manual. It should give you an idea of what it looks like.<p>Jspecmazdaman, so answear the last part of the question. Have you tested the TPS sensor? Do you even know what an ohm meter is?<p>One thing that gets me about this BB is how quick everyone is to give BS advice as truth. Give specs, where you got the info, if you've done the mod. yourself.<p>-Cybin

<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by jspecmazdaman:
Hey check the throttle positioning sensor on the back of the throttle body. Mine is doing the same thing and it is the TPS. I cant find one anywhere dealer wants 300.00<hr></blockquote>
How do you know? Guessing?

I had the same problem, wasn't the air bypass valve, it was a blown head gasket and baaad valve cover leak. Not saying it isn't the air bypass, just check your plug wires connectors for oil on them, or just take out your spark plugs just to make sure.