I removed my emissions and installed a BDC TB Mod and now my idle surges about 400 rpm like a heart beat. Inital start up it runs rock solid then after about 60 sec's it starts surging. The car is a low mile 89 T2 with a rebic 3 with 2.5"dp and exhaust it runs 12lbs of boost stock S5. Ask me what you will I have run out of ideas.
And it will do it if you give it steady gas the surge speeds up along with the excelleration.

 

Vacume leak.

Have some carb cleaner around? Start the car and spray it around the upper intake manifold, injectors, TB, and all intercooler hoses. If the idle changes at all (goes up)- you have a vacume leak . Check for missing hoses, anything that could cause one.

 

If you buy one of those propane torches; the little guys. You can use that also by taking the torch part off and putting a silicone hose on top. The propane doesn't get everywhere. You can also substitute this with butane. And just aim it at all the intake parts vac lines and everythign just liek the carb cleaner trick.

 

bad gaskets = vac leak
ripped hose = vac leak
sometimes things can come loose = vac leak

 

well... I took the intake back off and gave it and the lower a good going over and nothing is evedent. I'll check some more I unplugged the TPS and it didn't surge just didn't run smooth. and soon as I hooked it back up it started again so I checked the narrow bamd it's @ 1k and the travel seems smooth. I sprayed carb cleaner around with no change. Perhaps the TB itself has an issue?

 

It looks like I finally found so,ething I don't like about this car.

 

this is why I don't want to play with/remove the rats nest....
good luck

 

I removed my rat's nest and the car runs as smooth as before... maybe even better. I kept the BAC though.

 

all my emissions are removed even the rets nest. Car idles right at 1k. Havnt had any problems with it yet. Try doing the thing there you put a screw in the throttle inkage place (sorry im bad with words)

 

Ok every reply said vacume leak, so why when I turn the wheel hard left or right the surge magicly goes away? Anyone? I took the whole setup appart Three times and sealed every f$$ken possiable area where a vac leak could originate.
NO change until I turn the steering wheel and clock it all the way left or right? then the idle straightens out. WTF!!
Yes I unplugged all of the wireing going to the PS set u-p and with it unplugged it surged even with the wheel clocked so thdambed thing has something to do with it.
I figured that even on a hot start it would idle high but smooth for 30 sec's or so then it would start surgeing.

 

[QUOTE=Amazdaing]Ok every reply said vacume leak, so why when I turn the wheel hard left or right the surge magicly goes away? Anyone? I took the whole setup appart Three times and sealed every f$$ken possiable area where a vac leak could originate.
NO change until I turn the steering wheel and clock it all the way left or right? then the idle straightens out. WTF!!
Yes I unplugged all of the wireing going to the PS set u-p and with it unplugged it surged even with the wheel clocked so the dambed thing has something to do with it.
Even on a hot start it would idle high but smooth for 30 sec's or so then it would start surgeing.

 

Well Now I am baffled.
I disconnected the PS belt and all asocciated wiring and it still does it. It seems like it should be a vac leack but I'll be dambed if I can locate it.

 

I am pretty sure this is not a vac issue.
Any other ideas?

 

Fixed it and it had nothing to do with a vacuum leak. It was the adjustment of the TPS and the TB itself. I guess if your to far above your idle circuit with these cars you will have problems.
Once again a happy mazda owner.