hi all been awhile. once car warms up it will idle ok then drop a bit(from 750 to 300 rpm). it is not constant sometimes it will idle fine then start being funny. also when i get off highway and i put in N rpms drop strait down and either bounce back up or shut off. any help would be great this is my daily driver

i have not found any vacuum leaks. sprayed started fluid arould anything i could get to. thanks

 

For staters, you need to measure the voltage of the Green/Red wire found at the TPS plug to one volt w/key to on and the engine completely warmed up. Also, do you have the BAC solenoid deleted or connected properly?

 

ok the BAC solenoid should be connected properly i will have a look at that and my TPS and update tomarrow. thanks again

 

ok TPS and BAC solenoid are all checked and good. still jumpy and wants to stall when i get off highway or come to short stop. today the idoit lights came on then off as i was coming to a stop. any ideas???

 

The idiot lights come on when there is a problem w/the alternator. And the BAC needs to be working which requires more than just the plug being connected. If you were idling the car w/all the accessories on and you pulled the plug off of the BAC the idle should drop. If it does then the BAC is likely working okay. There is also a component on the rear of the throttle body that has a small White plastic nub sticking out of it that rests against the throttle linkage. It should come in contact w/the linkage when the rpm is at 3000 or so and this prevents the secondary throttle plates from closing too quickly on a quick stop, which can cause the engine to stutter and want to fall on its face.

 

ok thanks i will go check BAC. will check the linkage. that soulds like whats goin on when RPMs drop from over 3000 it wants to "fall on its face"(haha)

 

Ok so i got a chance to go and BAC. I unplugged the clip and no difference. So this would mean bad BAC right???

 

Did you have all your accessories on like the lights, radio, wipers, fan. And what was the idle speed before you unplugged it. Normally the BAC will keep the idle at 750 rpm when under load, but you removed the power steering and A/C, which are the two largest contributors to load so your results would differ compared to those cars w/those items.

 

alright i properly checked BAC and seems good(turned everything i had on and RPM dropped when unplugged and came right back when plugged in)

i also checked TPS again and all seemed well(still set at 1k ohms and goes smoothly to 5.1k at WOT.)

still cant figure out why it wants to stall when i RPM drop or at idle(sometimes does and idiot lights come on and then RPMs jump back up)

 

This sounds exactly like what my car is doing???

https://www.rx7club.com/1st-generation-specific-1979-1985-18/massive-dip-rpm-before-returning-idle-925172/

 

The mechanism I suggested you look at from the back of the throttle body is the Dashpot. Did you check its position relative to the FSM? As previously stated, the White stub is to touch the throttle plate mechanism when the engine speed is close to 3000 rpm. This mechanism can easily be adjusted either way to see if it creates for a better driving experience.

The idiot lights turn on when the engine is off w/key to on or when the alternator is bad or when the alternator is slowed down due to the engine wanting to die out which makes the idiot lights think the car is not running. You might want to measure the output of the alternator (Black wire bolted to the alternator is the output wire) while idling to see if it is 14 volts. Too low of an output could cause the engine to stall.

 

ok so the alternaor checked out to be good.

checked the Dashpot and was not adjusted right so i adjusted it and better but still wants to fall on face

i went back and checked my TPS for fun. yesterday i set it at 1k ohms and when checked today tit was 1150 ohms. is this sign of bad TPS??? back to being stumped any ideas???

 

Some people set the TPS to 1 volt on the Green/Red wire w/key to on when completely warmed up. You might want to go this route. And as long as the car does not die out then it's okay for the rpm to drop rather dramatically as mine does the very same thing as well as others too.

 

ok i will give that a shot. i more concerned about it dropping so that my idiot lights come on and it wants to die. i will go recheck TPS. thank you for help it just scares me when my car wants to die and i dont know why

 

ok so i went and set TPS to 1 volt and still not the cure. i went back and did resistance test on BAC it should be between10.7 and 12.3 ohms. it came back at 13.8 BAC valve bad right???

 

Ok so yesterday i set my TPS to 1 volt and when i got to work today i checked it and it was at .75 volts. Maybe TPS bad???

 

The rule of thumb about checking the voltage reading on a TPS is it "always" has to be measured under the same conditions which is when the engine is as warmed up as possible. Being close to warm does not count. If the engine has not warmed up properly or it has warmed up properly but has cooled down some then you'll get various readings. The Fast Idle Cam on the rear of the throttle body changes position relative to the engine temp which then moves the throttle linkage which then changes the TPS plunger which then changes its reading.

And after 25 years of usage a TPS can easily develop dead spots. Using an analog voltmeter is best to see if the voltage movement from low to high is smooth and free of jumpy or erratic movement. The voltage range should be between 1 volt when the TPS is set properly to close to 5 volts with the plunger fully extended. So as the throttle linkage fully releases from the TPS the voltage needs to smoothly rise from 1 volt to 5 volts.

 

Ok i was thinking that i didnt drive as far before ichecked this morning. I goin to recheck TPS and check Fast Idle Cam.
What about resistance check on BAC??? It was out of range is this something that should be replaced??? Cleaned???

 

I can't remember what is spec, but if it was fine one day then it should be fine the next day.

If the car idles at 750 rpm when fully warmed then you check the TPS when it is 750 rpm and not 850 or 1050 and so on. Doing this will make for different results.

 

ok so figured that tps was bad because every time i checked it it was different. got new TPS and installed and set. started right up lil jumpy for a sec but then like butter. then out of now where it started running realy ruff and black smoke started puffing out when i hit gas. now its jumpy and if i hit 3000 RPM it realy doesnt like it. i tried to pull forward and it fell on its face. can someone help me get my car off its face this is my only car.thanks

 

Is the TPS from another aged car or brand spanking new? If it's used then you never know what you are getting as it could be worse off then the initial unit.

 

I had that problem, i rebuilt the altnator and it took care of that problem

 

TPS is old but is off working car. But i thought it could still be bad. I checked my spark plugs and they are chared black. They were fine the other day. With "new" TPS it ran great for a bit then something bad. I goin to get new plugs and see. Wires only 15k on them new with last plug change. Anyone with ideas??? Thank you all for your time