so many people seem to have this problem so here is a quick write up on it.

I went through a ton of troubleshooting to try to find the most common causes of this problem.

most people would say its the tps, not exactly true.

here is a run down on how to fix it, and why it happens

this should apply to 99% of you, if your idle is pulsing between 800rpm and anything below then this may NOT be your fix.

#1 first check all vacuum lines around the entire intake manifold assembly, sometimes they get worn and slide off easily.
some may just need to be replaced.
This definetly applies to those of you who have just done work on the car and could have knocked one off.
A vacuum line will do it everytime, just un-plug one and see.
hint: check obvious places you can see first, then check against the firewall on the passenger side, behind the intake manifold. there are connections back there you cant see so well, three lines go into the intake at that point, follow them down to see if they are disconected.

#2 The throttle cable assembly, I found this gets gunked up very easily, mainly the return spring is not working 100%, or the cable just needs to be loosend up.
You can check this one by using your foot while the car is running to pull on the gas pedal.
yes pull not push, see if the rpms drop when you do this.
also push on this piece here, just like I am doing in the photo


see if your rpms drop, if they do try to clean this spring up a little, and adjust your throttle cable.


#3 this screw may hold the answer for you, very lightly adjust this screw, go slowly this is very touchy.
you will need a small flat head to make the adjustment.



thats it, three step process.

now why it does it,
Here is the best I can come up with.
your car is not meant to idle above 1,000 rpm.
not stock anyway, unless of course if its warming up.
and after it warms up it drops the rpms.
also if have every noticed in a variety of cars when the car is half warmed up it idles slightly high, but if you ping the gas pedal it will drop down.
well the car has this capability as well.
It sees the high idle and normal temp and thinks its ready to drop down the idle, when the idle raises back up due to a vacuum leak or throuttle cable or whatever the problem may be the computer drops it back down again, then it goes up, then the car says no I need you down, car says no Im going up, and up and down we go.

you get the point.

good luck

 

and if you read down on this page I have a fix for hard starting, well at least my fix.

https://www.rx7club.com/forum/showth...hreadid=173885

 

ttt

 

Hey great post man this should help a lot of us out if it works. What car did you perform this on?. My prob right now is i have a totally random idle. When first started my car idles at 1500 rpm, then when i drive it itll idle to 2k then after driving it all day it idle low somtimes at 800 other times at 1k and sometimes even it goes lower than 800 so its all over the place. Ill try the steps you posted. Thanks for the info

 

This was done on two 89's an 87 and an 88.

I dont think your symptoms sound like my fix will help, but its worth a shot.

I would try the tps in your case.

 

i don't think thats the same problem i'm having, help me out this is what it's doing. first is it's having trouble holding an idle, it will also jump or pulse at least 500rps and drop back down and go up etc...the other thing is when i'm driving it starts to do that pulsing thing and it becomes practically uncontrolable....the tires even start to cherp. any ideas??? i'm going to check TPS resistance tomorrow. i think thats whats wrong but i'm not sure
-Andrew

 

V8kilr: what screw, where? You don't say (in the #3 thing)

 

you know that screw by that piece, next to that wire, under the plastic piece, by the blue thing.....lol....yes where is this screw!!!

 

It was in the pic, which no longer works because this is an old post. He talking about the one between the TB and the UIM on N/A's that screws right into the TB.

 

Random idle or looping idle can be caused by faulty injectors. If you air/fuel mixture is off your injectors can be working overtime which causes them to heat up, and often time you can develope tiny splits in them. Leaky injectors can cause minor or major fluctuations in idle depending on the severity of their damage. If all of the above has been checked and is working properly, it might be time to check the injectors.............

 

are you talking about the cam screw

 

sorry had pics up, stops hosting them by accident, anyway its the very small one on the top of the throttle body, very touchy screw

 

I rode on this theory for a while myself, if you do some digging on my post in this section of the forum you will see I had much greater problems then the ones I mention how to fix here.

My biggest issue was the extremely leaky fuel injectors, the primaries were leaking in the engine, while the secondaries where leaking outside of the engine.

and even still with this going on I was able to pull off a very smooth idle with the process mentioned above.

It was getting the car started that was a pain, after I swapped the fuel injectors it helped a great deal instarting and running, but still wasnt my fix.

I later found that the brand new spark plugs were faulty somehow, with only 5 miles or so on them.

yes 5 miles not 5k or 500, or even 50

so I came to the conclusion if the fuel injectors were causing the problem, or were at least the main cause of the problem they would have to be so damaged that i question the cars ability to run at all.

just my 2 cents

sorry for any type-o's , my keyboard is a p.o.s. and I dont feel like proof reading

 

I was speaking out of personal experience............ And in the end, it all came down to my injectors!

 

Thanks for the re-post- I have been having a minor prob like this which dissapears after the engine warms up.

 

check the aws

 

mine only STARTS when the engine warms up. But I'm getting my injectors cleaned professionally and new o=rings and brackets installed, so hopefully that solves it.

 

i don't think thats the same problem i'm having, help me out this is what it's doing. first is it's having trouble holding an idle, it will also jump or pulse at least 500rps and drop back down and go up etc...the other thing is when i'm driving it starts to do that pulsing thing and it becomes practically uncontrolable....the tires even start to cherp. any ideas??? i'm going to check TPS resistance tomorrow. i think thats whats wrong but i'm not sure
-Andrew

 

Great info. I'm going to go to work on mine tomorrow morning.

 

post if run into any bumps along the way, btw you got a p.m. on the auto to manual conversion brackets.