high idle after mods pls. help

[Deusxmachine]

Hello everybody, I just finished modding my 90 coupe and now i have a pretty high idle. Here is a list of all the things i did:

cut air lid with K&N filter
Tpis big mouth manifold and large tube runners
52mm throttle body
pelnum ported
Hyper tech coil
180 thermostat
air pump eliminater
Tpis long tube headers
true daul pipes with borala stingers no cats
mat sensor relocation kit
also did a tune up, new plugs, wires, oxygen sensor, new egr valve,

I did all these mods at once over the winter. Now the car idles at around 1500-1800. It is also weaker and seems to be kinda of lean. I checked for vacuum leaks with propane and found nothing. I dont have a chip burned yet and some people think this is the problem. I didnt think i would get full power from these mods with out one but i figured it would idle right. Is there any thing that I could have done wrong or forgot? I would really apperciate the help, Im stumped and i hate to see the car sit through the whole summer :cry

p.s. where would be the best place to get a chip? Thanks for any help

 

[OLDCHEV]

Most throttle bodies I have seen have a screw to set the base idle. Are you sure this is adjusted right? The information center in this forum lists the proper procedure for setting the TPS and also mentions this screw.

If it is set too high, the computer might be compensating for the high idle by pulling fuel out thus causing the lean condition.

 

[Vettefan87]

Since you did all those things are you sure your throttle linkage is returning all the way to the idle screw? Doesn't the 90 still have the TPS, and the IAC or did they change that? If not you might want to check those, but I am not sure they were still on those cars. I would imagine your car would idle better then that even with the stock chip. You probably should get one burnt, but I have no clue who does that.

 

[Deusxmachine]

I have the screw set all the way back. I had the IAC replaced when i first got the car just a few years ago. Would a bad TPS cause a high idle? I thought that would cause it to run rich. Thanks for the replies

 

[jimmers]

Its good that this was brought up because my 90 vette idles at the same rpm. Curious to see what you guys say.....

 

[Deusxmachine]

Its good that this was brought up because my 90 vette idles at the same rpm. Curious to see what you guys say.....

Is your vette stock or have you changed anything?

 

[vetteboy86]

There was a fellow with the same problem not to long ago. Try a search for high idle or something close. The compute should not need the car to idle that high. Even when at start up, the fast idle setting is around 1100 RPM's. So I doubt that is the issue. I am not too familiar with the IAC, but if that is not right the car might idle high. Did it do this from day one? Also, maybe the filter was over oiled, and a film has deposited onto the maff wires. Does that still use a maf, or speed density?

The bottom line is, that the car shouldn't idle that high, with the stock prom in it. Are you sure you have no leakes, maybe around the throttle body. My first impression would be the throttle linkage not returning.

 

[Deusxmachine]

bump

 

[Vettefan87]

Your TPS could just need to be calibrated, it may have gotten bumped when all these mods were done. I know I have mine set to high, and it is idling higher then it should, but not as high as what you are describing. Check the small stuff first before you get into the expensive stuff. Your TPS should read somewhere around .58 volts or so with just the key on, and 5 volts at WOT. That is what my service manual says, I am not sure if it is the same for your car or not.

 

[Deusxmachine]

Thanks for the advice. How do you check the TPS, and if it is wrong what do you do to fix it

 

[Moonunit 451]

I have the screw set all the way back. I had the IAC replaced when i first got the car just a few years ago. Would a bad TPS cause a high idle? I thought that would cause it to run rich. Thanks for the replies

It seems to me that you need to follow the instructions OLDCHEV suggested, although I have not looked at them, there is a proper proceedure. The TPS can cause a high idle, but you can't just adjust your idle with the idle screw, you must adjust the TPS first. Could your timing have gotten bumped when you did your mods?

 

[Deusxmachine]

I was very careful to put the distrbuter back in the same way i took it out. My dad and I played with the timing a little but when we retarded it enough to make the idle seem right the car had 0 power. I just looked up the info on how to set up the TPS. Im going to try that this weekend. Keep posting any theorys or advice you guys have. Thanks for all the help.

 

[Hrtbeat1]

Try the temp sensors. Not necessarily the Thermostat. Rather the ones in the block and front lower intake manifold. They are thermistors and have multiple "ranges" that they operate in. They can operate perfectly in one "range" but be off in another. Throwing the computer a loop.

 

[jimmers]

Is your vette stock or have you changed anything?

everything is stock in it at the moment.....

 

[jan-erik]

High Idle

Hi. I have an 85,but the main adjustments should be the same.
First adjust the ign. timing to 6 degrees BTDC. Then check the TPS to be between .54V and .62V.
Then a very sure source of high idle or hunting idle is vacuum leaks. Check the hoses for cracks etc. Vacuum leaks you can fast check with spraying start gas or propane around the runner/manifold or places where you suspect there might be leakage. If the engine increases the rpm immediately there is a leak. With the leak the MAF ( if you have that) will not register the right amount of air and the EMC cannot correct the fuel fuel/air.
Check also the PCV valve for proper operation. As you have the 52 throttlebody the minimum air idle adjustments has to be performed so that you have about 450 rpms with the IAC valve closed (see manufacturers manual).

 

[WhalePirot]

The '90 is a speed density system and has no MAF. It is also relatively unforgiving of mods. It computes the amount of incoming air using MAP and other inputs.

I submit that, after checking the mechanical and voltage settings, that you may be seeing the ECM trying to adjust for your mods, but is unable. It can remove fuel to try to slow the idle, which would explain the leanness and perhaps, the lack of power. If this is true, a custom chip is indeed in order. If you cannot check the block learning, call TPIS and ask if the parts you installed demand a new chip.