I just got done planting an 88jdm turbo engine into my 88 convertible. Car has a straight pipe/no muffler and conefilter with stock TID. Car starts up no problem evertime, idle stays at 1800 for about 10secs then goes from 1250-1500-1250-1500. I have removed all emissions including the bac, set the TPS to 1ohm, sweeps perfect all the way to 4.5. TB plates are all set to spec, pop'd the top off the cas and the pointers are in the right position for it to get a good idle. I cannot hear any vac leaks, replaced everysingle vac line with new one, along with intake gaskets. There might be a very slight exhaust leak from using "used" gaskets. My jdm tranny, the hookup for the closed loop and 5th switch was too short so it is not hooked up right now, is the loop system making my car run too rich? Car doesn't back fire big or anything, rev it up and hold it at 3k and theres a very slight popping which is normal? Car pulls -17-20 vaccum when idle at 1250-1500. Car doesn't act like it wants to stall at all, rev it up let off the gas and no backfire. I have not taken the car over 3.5k for fears of leaning out. Gas is 3months old and 1/3 87, should I throw some booster in there? I've spent atleast 5hours searching and reading over the past 2 days but my fragile mind still needs help.

Thanks, Tony

 

Hmm, we've all said it time and time again, hunting idle is caused by two things

1)tps out of spec
2)vacuum leaks

Since you've covered #1, find the leaks and you'll eliminate the hunting idle, I gaurentee it.
Check the archive and find that post on getting a rock solid idle. It covers EVERYTHING that can leak for the intake.

 

my engine did that too awhile ago... it waz a vac leak.. i never found out where but whrn i put a diff engine in and put new vac hoses and vac caps problem solved

 

have you tried adjusting the idle at all? it sounds like you just started it up and expected a perfect idle without touching it. explain anything you have done to try to get idle down and if you havent tried then read the fsm section on it and see if it is still messed up

 

Even if you could adjust the idle screw (or bac screw for TII) all the way out, it should still not jump up and down. This is becuase the ECU is prepared for the full range of the idle screw setting. If you turn the screw all the way out, and your getting a up down idle, then you have a vac leak still in the system.

 

How can you hear a vac leak with that exhaust?? kinda kidding but kinda not. Not trying to make you angry but still wanting to question.

 

You probably can't. I don't even know how I'd start to pick and choose what to replace in terms of grommets, gaskets and vac lines for a vac leak personally... Thats why if I get another FC, I'll just rip it all off to shortblock and replace it all, last another 17 years...

 

You can't. What you have to do is spray carb cleaner around all of the vacuum fittings, one at a time. When you hear the sputtering idle, you've found it. Don't forget the brake booster line. Mine was all cracked and leaking like crazy on the exhaust side line.

Like blackplague just suggested, I had replaced all of my vacuum lines at once. I used red silicon hose so that I could tell which ones I had replaced. It's much easier than troubleshooting a hunting idle every couple of months.