wickedrx7

iTrader: (14)

First want to start off by saying that I did search and read a LOT of threads about surging idles and got all kinds of different answers. This is the one that makes the most sense with me is this:

Originally posted in this thread
https://www.rx7club.com/forum/showth...hreadid=306554

Now that I have that out of the way, my mods are
Medium street port
PFC
M2 Air box
M2 intercooler
Full exhaust
Non-sequential
850's all the way around
No emissions

Problem 1) When the car is cold it idles good, but once it warms up above 80 deg Celsius the idle will bounce from about 900-1500 rpm. If I let it idle for about a minute, it will calm down and idle perfect at about 800 rpms.

Problem 2) (Might be related) Sometimes when the car is off and I have the ignition on my Idle Speed Control will start buzzing really loud. I don't know why it does it, but it does. I tried unplugging it and it just dies. I suppose I can unplug it and set idle manually, but really don't want to do this.

Questions:
1. Is the ISC related to the fluctuating problem?
2. What is causing the fluctuating idle? (From reading it could be a lot of things)
3. Is this problem going to hurt the car or should I just unplug it and set the idle manually until I get the car tuned?

Thanks for the help, and Mods please don't move, there is a similar thread in the PFC forum and I think this is worthy of this forum.

rynberg

The symptoms I had when my ISC went bad were:

*car would surge between 500-900 rpm with the A/C on
*idle would drop noticeably when an electrical load was applied before bouncing back to normal

Unfortunately, the ISC is expensive ($250 for the part I think) and you have to remove the UIM to replace it -- good thinking Mazda!

clayne

Unless I'm missing something, you don't have to remove the UIM.

I just replaced my ISC gasket on Sunday with the UIM completely connected.

2 10 mm nuts and you're done.

To the original poster:

1. Check all grounds.

2. Reset PFC.

3. Check throttle stop screw. It should not have the throttle excessively pre-opened.

4. Check the air bypass screw underneath the intake elbow and located on bottom of TB. Adjust this until closed, then open it about 1/4 turn.

5. Verify secondary throttle plates have a small amount of delay in opening.

6. Do the 10 minute/10 minute defrost/10 minute A/C PFC idle recalibration. No matter hoiw crazy the last step seems - do it.

wickedrx7

iTrader: (14)

1. I have plenty or grounds
2.Tried twice with no luck
3.Will check
4.Shouldn't have changed, but I will check it.
5.Are you talking about the double throttle, if so I eliminated this.
6.Do you have any more information on how to do this, I have never heard of it.

Thanks for your help.

rex u.k

#6-You basically let the car idle for 10 mins. each, first with no electrical load then 10mins. with your defrost ......

rxgrun7

I have a 93 FD and Im having trouble with my idle as well and no one seems have the same problem as me. Here goes nothing. I bought the car with enfini Y pipe, 3" down pipe and 3" thermal research exhaust and 27k miles on a stock rebuild. one day i decided i wanted it to be louder so i went and got a 3" mid pipe fut on about 2 hours later of normall city driving. I pulled up to a stop sign and it was idleing very rough then died. Started right up again but very poor idle, and a check engine light. Took the car to local mazda dealer and the could not read code tech said ecu was bad so i bought a PFC and put that in but still no luck. please help me. Im so pissed off and broke too boot. Ive replaced a couple of hard vacuumm lines a pcv a intake air thermosensor and a TPS. need help

1QWIK7

iTrader: (33)

^^Sounded like you just popped your engine.

You should have bought a PFC BEFORE your midpipe.

And i dont think all of a sudden the engine will die during "normal city driving".

Chances are you wanted to feel power difference from midpipe install, and overboost and kaboom.

Sorry dude but you need to compression check your engine to find out and better start asking people for money if you're broke.

rxgrun7

Alright you caught me on the normall driving thing but I only got it one time in 2nd gear and and didnt even redline it cause I had to slow down. but i dont have a comp checker so i did remove one plug off each rotor and had three good puffs from each. But I will look in to getting one this weekend thanks boys.

arghx

iTrader: (3)

^^ there are all sorts of tuning mistakes and misadjusted throttlebody stuff that can make the engine day during normal driving. You can't assume a blown motor necessarily, although a compression test is not unwarranted.

Take it from someone with at least 50 hours of hands-on PFC tuning experience on both the FD and the FC. Fuel tuning is a BIG part of it. A lot of times if your idle is too lean it likes to surge, especially on hot starts when the IAT sensor heatsoaks and PFC leans out the mixture to compensate for hotter, less dense air. But if you don't back off the screw in the TB your idle will definitely stick or surge.

rxgrun7

Hey guys I know this sounds crazy but I got in my car today and used the PFC to turn off the ISC valve it runs perfect without the air on now at idle and under load its fast again but still surging with A/C on dont understand really but Im doing the 10/10/10 therory to see if that will work.

a-card

try a new engine haress

rxgrun7

Damn Mazda remans. I found out that in fact the motor was blown so I pulled is three weeks ago and actually rebuilt it myself. I did do a lil port work while I was in there though . I finally got to rip in to it the other night and wow that bitch halls *** now I love it and the fact that I built it myself is even better you know. I had alot of fun and now im actually doing a couple of side jobs for friends. I m experimenting with a periphrial right now for a friends baha bug its so much fun to build them. next Im gonna try a bridge port. wish me luck!!!!