Damn High Idle - HELP

[Rice Burner]

Ok, here's my problem. My 1990 GST has high idle and I've been chasing this and idle surge for over a year off and on (this isn't my DD). I got the surge figured out a while back and had been chasing the high idle issue after that. I have tested for boost leaks several times and have found quite a few which have been fixed. I had leaks in the BISS, TB seals, TB gaskets, Injector o-rings, PCV hose and probably a few more. I have changed the TPS, replaced the ISC with newer black one, replaced ECU and the IPS all of which were bad. I have adjusted all of those recently since I had my TB out to do the FIAV block off. Oh I also had a broken wire on my Coolant sensor which I fixed.

So I get the TB back in yesterday and do some adjustments and set it to idle at 760+/- as instructed in the VFAQ and it's doing great for a few minutes when all of a sudden the idle just starts creaping up to around 1400 rpm and I'm like WTF . I go back and ground the terminals and go to reset timing/BISS but not working and still idleing high.

I have spent days searching online before this recent event and hours last night on this site and others but I can't find anything else to try. Could something have gone out and caused it to shoot up like that?? I'm pretty fustrated at this point and need some ideas??

Also I recently got a pocket logger setup with MMcd and I'm starting to figure out how to do a few things on that so if there is something in particular that I should look out for that may help please let me know.

Thanks for any help!!

 

[pauleyman]

Are you sure the idle position switch is working? The ground must exist between the throttle body and the intake manifold and there is another ground wire between the intake manifold and the firewall. This is what allows the IPS to work. I've seen so many throttle bodies that were missing the ground at the front. It's a bracket that appears to do nothing but it's quite important that it be there.

 

[Rice Burner]

yes the TB ground is there but I've never noticed the intake to firewall ground. Not saying its not there I've just never noticed it. Where exactly is it? Also the TPS is working because I just replaced mine that was dead. I wonder if it's adjusted correctly? I did it with the meeter and turned it down 7/8 from where the meeter got a reading. That doesn't leave a lot of room to mess up. Would that cause it to idle high after several minutes of 750 rpm idle? I'll try to reset that again tomorrow.

Do you know what should my ISC read on my logger? My TPS reads 10.5% at idle.

 

[pauleyman]

There are only a couple possibilities for high idle. Air gets in somewhere either via biss, FIAV, ISC or leaks. If ISC is working and can be set correctly that pretty much removed that issues. Biss is a simple orifice, you could completely close it just to see what happens. That leaves FIAV (do you have coolant lines hooked up) and any possible intake leaks after the throttle body. The idle can't go above 1500rpm with a working IPS. Which reminds me....one other possibility. Throttle cable. I've seen them adjusted too tight and the throttle may actually be slightly open with no input on the gas pedal. The sleeves can also slide out and get stuck on older cables.

 

[Rice Burner]

Thanks for the response. Yes I have gone through and found all the boost leaks that I can find and even rechecked on Monday after doing the FIAV mod to be sure (no coolant to the TB any more). I even went as far as doing the TB cleaner spray method on various parts of the engine and all came up clean. The throttle cable has been adjusted to be sure it's not too tight. I have the BISS turned all the way in and it idles at 1400.

Tonight when I get home I'm going to check the ISC and see if that may have gone bad even though I just replaced it about a 8 months ago. It was used (newer black style) but I remember when I put the TB back on I was adjusting the (damn forgot what it's called) black sensor that attaches to the throttle shaft on the side opposite the TPS and I felt the ISC getting pretty hot so maybe that got fryed somehow. It wasn't flaming hot but for not even running yet it was pretty warm. At that point I disconnected it until I was done setting the other sensor then plugged it back in. At that point it was idleing fine and I get the BISS and timing set. It was puring like a kitten for about 5mins then started creaping up and never came back down since then. Hopefully the computer didn't get damaged because I just replaced it also along with the ISC last year.

Does the ISC cause steady high idle or just idle surge?

 

[1995mitsuGSX]

When my isc went bad it caused mine to idle high after driving it for a couple minutes. It was intermittent and related to heat i could drive all winter with no problems but as soon as it turned warm id have problems. So isc can cause both surge and constant high idle depending on how far gone it is. The good news is there super easy to test and find out if its the culprit. Theres even a video on youtube of jafromobile testing one.

 

[BurrowZ]

Does it only do it when it's warmed up? Is your throttle cable too tight?

 

[92AWDHX40]

Terry's Talon Troubleshooting Tips #3 - Fast Idle (aka. Idle Surge)

it says surge but it can also help with idle,great reading material.

 

[Rice Burner]

Does it only do it when it's warmed up? Is your throttle cable too tight?

It did do it after it was warmed up and running for probably 15 mins total. The first few minutes I was waiting to warm it up so I could do the BISS/Timing. The car isn't driveable at the moment I'm just getting it running from sitting for several years in a garage.

I have read Terry's Tips religiously from past idle issues and this is kind of the final issue (I hope). I'm leaning towards the ISC since that's the only thing I haven't actually had a meeter on since I put the TB back in and I just rechecked for boost leaks on Monday and found none. If ISC is the problem I'm praying it didn't screw up my ECU. I'll be pulling it out and testing it this evening when I get home and I'll update what I find out.

 

[mnim15]

I had a similar issue and ended up swapping out my MAS too and it has now been several weeks without having the issue.

 

[Rice Burner]

Ok I got home and pulled out the ISC (newer black version) and tested with my meeter. It was showing 43 ohms and I had a older tan colored version so I tested that also and had 31-32 ohms. I put the tan one in the TB and went through and rechecked my TPS and reset my Throttle switch. I cranked the car up and it was idling at about 800 rpm and all was good but eventually the idle started shooting up to about 1400. It almost seems like once it warms up something happens and causes the idle to jump up. At one point it seemed like the Throttle stop switch was not adjust correctly and was causing the throttle plate to stay open but that ended up not being the problem even though it seemed like it. Not sure what the hell is going on at this point.

 

[agarcia]

Does your car have a CEL code?

 

[Rice Burner]

No no codes.

Well looks like I got it idleing like when it was new. I ended up just buying a TB from Throttlebodies.com (steve) and put it on yesterday evening. Reset all sensors and fired it up. Works like when it was new and he did a great job on the rebuild. FIAV works and it eventually settles on about 780 +/- after a few mins . I think when I did my FIAV block off I must not have done it correctly since I was still getting the same "high idle" as before and this TB works as it should.

The only problem I'm still having is there is a 1 sec lag when I hit the gas then it reves up. I did set the timing as to 5* BTDC (grounding the firewall pin and the data logger port in the car for the BISS). However my logger shows my timing bouncing around between 8 - 11* and idling at about 750 - 800 rpm. So not sure if the timing is causing that throttle lag but i would suspect it is (?).

Next issue to tackle on the list will be steering rack which all the fluid leaked out of (it's been sitting for 8 yrs..) so I'll probably just get a rebuilt replacement and mark that off the list.

Thanks for everyone's help on the idle problem!!!