1G Idle mystery problem on 1G

[robciao]

I recently upgraded my 1G to an SAFCII, 550's, and a larger side mount IC (Supra), and the Al Blaha modified MAF. When it was all dialed in on the SAFC and fuel trims near 100%, it was running awesome, with idle perfect.

Then, about 3 weeks ago the dreaded rmmm, rmmm, rmmm idle surge. The first thing I checked was a the ISC unit. Sure enough, bad coil. Found a good one a a Bone Yard, checked it out thouroughly, and popped it on. No luck. Still got surge. Hmmm.

Check for vacuum leaks, etc, nothing is yet apparent. Here is the mystery, and within probably the answer. When you first start the car cold, it idles at 2,000 for about 1 minute, then rmmm rmmm rmmm idle surge...UNTIL the engine reaches normal operating temp (coolant temp at about 190+) and then it idles fine? I can drive it all day while the engine is warm and it idles fine (although every once in a while when the rpm's drop really fast 2000k and let off throttle all together, it wants to die, like the ISC does not react fast enough to catch it).

Any ideas appreciated, it really makes me wonder why the problem goes away when the engine is warm.

 

[AwdEi]

Sound like the FIAV (fast idle air valve). It has the coolant lines going to it under the TB. You can replace it, the TB, or just block it off. You dont get too much from the mod, just not having 180+ coolant running through your TB raising intake temps. The down side is it idles high until warm, but I dont have this problem.

If you do get anything from a junkyard, go ahead and get a 1g N/T TB. it is bigger. Just make sure it looks like the turbo TB. Some of them are a little different.

Hope this helps.

 

[thehyena]

the 90 tb's are different from the 91-94's

 

[EHeye]

datalog it and see what it is doing. Try adjusting the BISS, or it could be a bad TPS, the rmmmm rmmm rmmm says sorta TPS.

 

[robciao]

Thanks for the replys!

Couple of more questions:

I've seen pictures of the FIAV, and from my understanding it has wax in it, when the wax heats up and melts it opens or closes some air passage. Since its not "mechanical" does it ever fail? Also, is this part replaceable as a seperate item from the lower throttle body or not?

I have been Dataloging everything. Wierd thing...when it goes into rrmmm rmmm mode it almost looks as if the the injectors (injector cycle) is cutting out for a fraction for a second. Could this mean my TPS is bad or going bad and telling the ECU the throttle is closed then correcting?

How do you check out a TPS? I have an AFC and it looks as though the TPS is reading smoothly, but I guess the bottom end of it (near closed throttle) gets the most wear, and maybe its worn out on that part of the rheostat?

 

[00 Agent]

If you go into "sensor check" mode on your SAFC you can see what voltage the ECU is getting from the TPS. It is sensor #3. It should read 0v closed and 5v at WOT.