1991 mazda rx7. did an 86 n/a swap. everything was fine until the lower intake manifold decided to crack at one of the bolt eyelets. removed it, replaced it. now, the car doesnt want to accelerate properly. around 4000rpm it stops and doesnt want to go any higher. slow acceration, it accelerates fine. tap the throttle to rev it, it backfires very loud and wants to die. i think that it might be a vacuum leak, but i cant fine one. i checked everything. it gets fuel, it has spark.......the leading plugs are burning properly but the trailing plugs are a little wet when pulled. i messed with the timing, but that did not work. it idles if you hold your foot on the pedal for however long you want. soon as its given throttle, it bogs and backfires. let off the throttle, it wants to die. any suggestions? i could really use some rotary knowledge from fellow rx owners.

 

well, im no genius but it could be a really bad 3800rpm hesitation, my car had it really bad. might be worth looking into, hope this helps.

 

i dont even think that could be the problem. that is an easy fix. it never did this until i put in the new lower intake manifold. i think that it is a vacuum leak, but i dont know where else to check unless i pull out the insert rods for the actuators and jb weld the holes shut. what do you think?

 

well, i figured out what my problem was. when i put the manifold on, i didnt have a new gasket for it so i used blue rtv gasket maker/sealant. apparently it does not work. words of wisdom to anyone who reads this. i never did that before until now, and now i know no to do it again. if you dont have a gasket, make one using sheet gasket from a local auto parts store. it might cost you $10 at the most. then put the gasket maker/sealant on it. DUH!!! i feel stupid.

 

3800 rpm hesitation only happens when there is a bad ground. easily fixable, cut or splice into the brown wire with the white stripe located on the connector to the vacuum/boost sensor. using an additional wire, attach to brown wire with white stripe and ground to chassis of vehicle. wala! problem solved.

 

well, nevermind. it is still doing it. it will idle all day long. its only when i give it fast acceleration is when it bogs. if i just hold the pedal down, rpms drop and it dies.

 

Sounds like your CAS may be one tooth out.

 

the sensor, or the gear in the housing? if just the sensor, i have an extra one. i will switch them and see what happens

 

clogged cat?

Slim chance I know but my 8 had the exact same symptoms.

 

straight pipe from manifold. checked all of the fuel system components: pump, filter, injectors, pulsation, regulator, and lines. getting spark. getting fuel. timing is right. maf works fine. tps works fine. ????????????????????spark plugs fouled out??????????? that is the last resort. i think that it might be the prob. got to wait til mon though.

 

bump..

every single sensor is functioning properly as well. ??????fuel relay by the passenger headlight?????

 

Stabbed incorrectly.

Based on what you have said in other threads regarding timing, this would be the first thing I would check on your car.

 

what does that mean, stabbed incorrectly? not familiar with that term.

 

I had the exact problem that you described!! The problem turned out to be a small slit in a silicone coupler in my intake track between the air flow meter and the throttle body.

 

there are no silicone hoses, they are all stock, but i will check the intake hose as you said. maybe there is a problem there. would it do that if the mass air flow or ecu is failing?

 

it has no leaks in the air intake hose or coupler. when i gradually rev it, it works fine. when i punch it after i gradually rev it, the rpms just drop or bog up and down, backfires, and then it wants to die. it also smells horribly like fumes and i have to leave the garage b/c it is so strong. i dont know what the problem could be.

 

as far as stabbing the CAS, what aaron means is that when you put the CAS back in (aka "stabbing" it) you accidently put it in one tooth off (you let the gear spin when you shouldnt have). search "CAS" and you'l find the proper procedure, its been written out 1000 times.