Bad Idle surge problems, also Idle down

OrangeMustangGt · Nov 13, 2004

ok ive messed with everything, what settings should i use on my IAC, and tb? my car lopes like crazy when it fires up, so i had to turn the idle up to keep it running, but i also have a problem, it takes forever to idle down, it stays at 2,000rpm for ever then finally goes down to 1,000 after a minute. Now, i uplugged my IAC, and once it was warm, it would idle down fast, like it should, and idle correct, however with the IAC unplugged it wouldent stay running when cold. please help, could my IAC just be bad, or can you clean them? it seems like a problem that has started since my new motor. my FP is around 35 now.

95strokerPSU · Nov 13, 2004

Sounds like I have the same problem as you with the horrible idle that feels like it's going to shake the car apart and the RPM's getting stuck at 2,000. Tomorrow, as long as I can get a new water pump, I'll be working on my car with my mechanic and hopefully figure it. He thinks the A/F might be running lean. But we're going to check FP, timing, A/F, IAC, etc. and hopefully figure it out. I'll let you know what we find out.

OrangeMustangGt · Nov 13, 2004

yeah man ide really appreciate that, tommorow, i think ill clean the IAC with soem electric cleaner, dont know if it will do anything, but i think that that is the root of all my evil. my car lopes so bad when its cold, it just dies, then after about 10 lopes, it smoothes right out and idles at 1,000. however i still have the bad hanging idle problem, wish i had a tweecer to change the dashpot setting.

95strokerPSU · Nov 13, 2004

I don't know if you're using the stock MAF or maybe a pro-m like I am, but I found this four step process on pro-m's website that sounds like it should solve our problem. "1. Set the throttle by removing the connector from the idle speed control motor. 2. With engine warm and air conditioning off, set idle speed at 700 RPM using the throttle screw. 3. Reconnect idle speed motor and check for engine stability. 4. Check system for vacuum leaks and fix them." Don't if this will help but I'm gonna at least try it tomorrow.

Silver85TC · Nov 13, 2004

First of all, set your base idle speed as detailed above.

Next, your idle trim screw may not be adjusted correctly. (not to be confused with the throttle plate set screw). The idle trim screw is the one under the little rubber plug beside the IAB valve. Try turning the screw in all the way, then opening it up one complete turn. On a car with the throttle plate correctly set, the trim screw will have a direct effect on how quickly the RPM's drop to idle and also how smooth the car is at idle.

If I open the idle trim screw more than a turn and 1/2 or so on my car, the idle hang's at 1600 rpm at stop lights. If i turn it back in to 1 turn or less, the idle drops very nicely to approximately 700 rpm at stop lights etc.

Hope that helps

HISSIN50 · Nov 14, 2004

GreenMustangGt said:
ok ive messed with everything, what settings should i use on my IAC, and tb? my car lopes like crazy when it fires up, so i had to turn the idle up to keep it running, but i also have a problem, it takes forever to idle down, it stays at 2,000rpm for ever then finally goes down to 1,000 after a minute. Now, i uplugged my IAC, and once it was warm, it would idle down fast, like it should, and idle correct, however with the IAC unplugged it wouldent stay running when cold. please help, could my IAC just be bad, or can you clean them? it seems like a problem that has started since my new motor. my FP is around 35 now.

have you checked vacuum? sounds like a vac leak if all else pans out.
good luck.

OrangeMustangGt · Nov 14, 2004

yes, woah thanks guys that's exactly what i needed for the adj. Now, one more thing, aside from sound, ai theer any other good way to check for vac leaks?

RIO5.0 · Nov 14, 2004

GreenMustangGt said:
yes, woah thanks guys that's exactly what i needed for the adj. Now, one more thing, aside from sound, ai theer any other good way to check for vac leaks?

have you put a vacuum gage on it yet??? they can be had for like 10-15 bucks..plug that in and start it up...the needle will show whats going on...
try it at idle .... then brings the rpms up some and see whats happening again...it wont pinpoint the location, but will tell if somethings leaking by the flucuation of the neddle...steady thru the rpms is good....jumping needle is a sign of leakage...
remove your FPR vac line and plug the gage there...its gravy....and will answer your leaking question...

95redSVT · Nov 14, 2004

This kinda sounds like what my car is doing (and has been doing for about 3 months now). Surges wicked bad only mine does not stop. It will surge for as long as you let it run. The RPMs go up sparaticly when you push the gas, come down wicked slow and in little jumps, then when it hits 11-1200 rpms it just starts galloping like the pony she isnt. Plugs are black and soaked in gas, Oxygen sensors are as white as fine dining china. no exhust leaks, no blown seals, cant find a vacuum leak. Im about a month away from taking it to the dealer and letting them play with it.

HISSIN50 · Nov 14, 2004

Rio, nice post.
i dont know what healthy SN 5.0's see vac wise, but foxes are in the 15-20" range at warm idle.

Bad Idle surge problems, also Idle down

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