90 GSX idle surge after warm up

[abakja1]

I have idle surge after my car is warmed up at around 2k to 2.2k,..

I have a 90 GSX and had boost leak at 1-2 psi after complete engine rebuild,.so I swapped in a later 90 TB wtih new oil seals and to do the FIAV blockoff and reroute coolant lines,..ISC was rewired because of harness and different TPS put in,..Previous to TB swap, never had idle surge,..So,..Im taking it the TB swap with different sensors and FIAV/Coolant line disconnected has something to do with the idle surge,.....

This is what Ive done/have:

Bypass vacuum lines as per taboospeedshop.com
Blocked off EGR
Blocked off FIAV with ATV,..I live in Hawaii so cold weather isnt a problem here,...
Adjusted BISS, new Oring/screw
Adjusted TPS
Swapped in 2 different ISC now to see if ISC is problem.

My car will start up cold and I may have to adjust BISS to get it to idle, but when the car is warmed up, the revs increase to 2000 rpms and surges to 2200rpms or so,...

What do I do now? Ive read I can disconnect the ISC harness, but have to rev car at cold start till it warms up....After warm up car is fine thereafterwards ,..But is there a fix without having to completely disconnect ISC harness?

Kevin

 

[steve]

Keep in mind that idle surge is caused by too much air at idle.
I forget the numbers off the top of my head but once the ECU sees the coolant temp in range and the Idle Position Switch is closed it monitors the RPMS and adjusts the ISC trying to get 750 rpm. If the ECU sees the engine running over about 2k with the IPS closed it cuts fuel then turns it back on once the rpms drop. over and over.
Figure out why your getting too much air at idle and the problem should go away.

Steve

 

[crankbender]

http://www.dsm.org/how-tos/tttt/tttt3.html

Everything you need to know about idle air flow paths.

If you are idling high it is because you have too much air. Additionally if it seems temperature dependent you may want to check your temp sensor.

 

[abakja1]

Ive given up for today on this,..Will try to figure it out if it is the ISC and it's connection to a soldered wire harness. Was rewired due to difference in wiring harness of my original May 1990 TB and this later 90+ TB,..

I need a helping hand to figure out if the ISC is stuck open or if it is moving in/out with the turn of the key to off and ACC,...Im on my own right now on this and doing what I can to track it down to the best of my abilities, but to no avail,...

I looked at the link and printed it out and checked off most of its causes,..again, Im thinking there is something wrong with the ISC or not completely blocked off FIAV although upper right hand side of passage was RTVd,....

Kevin

 

[abakja1]

Would it be a good idea too to JB weld or RTV the open slot at the bottom of the throttle body too? Im talking about the slot below the throttle body plate where warm air would enter the throttle body when looking at the TB plate from the FIAV,...Ive already blocked off the sections of the FIAV, but wonder if blocking this off too on the top side of the TB would help any with excess air/leakage,...

Kevin

 

[abakja1]

UPDATE:

I decided to put back in an early 1990 TB (May 1990) to see if the later TBs that Ive been putting in and swapping had anything to do with the idle surging that Ive encountered with,..I was trying to put in different later 90 TBs to make sure my original TB didnt have any seal leaks and cause I wanted to do the coolant blockoff with the later 90 TBs,..

When I put the early style May 90 Tb in, my idle surges dropped to around 1200 rpms instead of the 2k-2.3k rpms,..Maybe the different TPS and wiring harness was the difference? But I still had some surging and I could hear a big air leak somewhere,..

The TB I got EBAY was a working one so says the previous owner, as he said that he got it off his working Talon,..So I asked a friend to do a boost leak check for me as I had unsuccessful attempts,..Seems I couldnt pressurinze the system at all,..

Theory of 2 brains are better than 1 is true, as we took off the TB and found that the later TB gasket for June 90 and above TBs Ive been using isnt covering the original May1990 TB enough,..air was escaping thru the bottom portion of the TB that the gasket wasnt covering,..Guess the air passages are different between the 2 TBs thus the different shape of the gasket,..

Hopefully this is the problem as I will try and get a TB gasket this weekend and start er up again without any idle surging I hope,..If it does surge, at least I can perform a leak test now to check for any other leaks,..

Kevin