Daniel6718

has symptoms of a vac leak but ive checked it....cold start my car idles high...cant figure it out...i can drive 5 minutes and it will still idle at 1500-1800+ at lights...but 5 seconds after i start it if i let the clutch out and bog down the motor 3 or 4 times it will idle down to 1000 and stay there just fine...

i removed the t/b and cleaned well...check for vac leaks...but its perfectly fine after it idles down, like it has trouble searching for idle...but it doesnt change just stays at 1500-1800...if i let it sit and idle it will take about 45 seconds and it will idle down to 1000

car also idles rough at around 1000rpm....but i think thats the tr6 plugs with .035 gap causing that

mods are longtubes k and n cold air...tr6 (might cause rough idle???) poly motor and trans mounts...bmr subframes...lca/relos thats it....nothin on the motor tranny or car is older than 9k miles...

also notice someimtes that my car slowing down to a stoplight in neutral it will idle from 1200-1500 surging slowly...which i dont think is normal...any ideas?

put it on a smoke machine found a small leak on a vac line i capped so i got a plug and plugged it(it was the old egr vac place) replaced pcv valve and checked the brake boosted 90 fitting it functions fine

also forgot to mention this car hard starts...im thinking that something is going to fix most if not all this in one shot just not sure what is it....

fpr vac line is fine fpr doesnt leak gas...vac canister vac line and check valve to the a/c controls are fine
checked vacume and its 18-20 at idle
iac was around 29 at idle...never went below 25 or above 35...perfectly normal
o2 were both boucing around like normal...neither was lazy...blm i think were around 120....
weird though the desired idle was 800..but on the scanner it said it was idleing between 920-960
the gauge matched the engine temp on the scanner...it read 185 at idle...with one fan on
any other ideas....you can pump the brakes and it ides the same when you stop pumping them the idle goes up 2-300?

BoogieZ28

If you cannot find any vacuum leaks I would advice you to check the AIC (Air Idle Control) might need replacing. It is what controls your idel speed.

Injuneer

Idle speed is increased at low coolant temps. The exact idle speed tables are a function of the trans type, which you don't have in your signature. The 800rpm desired idle would indicate that you have an M6, if that's the value when the coolant is warm and its a stock program. But, its not likely you have a stock program with a cam. Maybe adding some actual info about your mods would increase the chances of getting the correct input.

If the idle speed is higher than the desired speed, the PCM should start to close down the IAC motor. Your data indicates that isn't happening. With a vacuum link, the IAC would close down to "0" counts if necessary to bring it back within specs.

The PCM also elevates the idle speed when the vehicle is moving. It shouldn't surge though.

TobyZ28

Injuneer I think you should change your sig to something saying people should put their car info in their sig

Injuneer

I'm writing a "how to get your questions answered" post, that we can "sticky"..... not that anyone ever bothers to read the stickies

I'm still debating the value of including a dictionary explaining the difference between...

brake - break
hole - whole
arc - arch

etc.........

Daniel6718

sorry guys i forget to mention this is on my daily driver..car in my sig is differant...makes it confusing owning 6 f-bodies.....i posted the mods above thought i was clear


mods are longtubes k and n cold air...tr6 (might cause rough idle???) poly motor and trans mounts...bmr subframes...lca/relos thats it....nothin on the motor tranny or car is older than 9k miles..


i see what your saying injuneer...but i replaced the iac with another i had sitting around and still the same problem is there....makes sense it acts like its idleing fine...but even the snap on scanner says its idleing 920-950 when the tach says 1000 and when im driving(which i havent with the scanner because its not mine) it sayys its about 1400-1600 so i know its too high

TobyZ28

May be way off here, but it might be a good idea to check your battery connections and grounds just in case (Since you've covered the IAC angle already). Electrical gremlins can manifest in a many different ways

GOFASTER

Is there a fuse for the AIC? I tested mine with a meter and it was fine, but when I tested the connector, it was an open circuit. I am having the same problems with my car, btw. It starts out with a low idle and progressively moves higher until it is at 14-1600 rpms in nuetral. In drive it goes about 1000 rpms. I have checked for vac leaks and can find none. My car is stock except for a CAI.

Injuneer

The IAC connects directly to the PCM. Shoebox has a method for checking the IAC motor itself (maybe you already used that to check the IAC???). The page includes a wiring diagram. There is no fuse:

http://shbox.com/1/iac2.jpg

You won't see any voltage at the connector, unless the PCM is sending the short pulses that move the stepper motor in the IAC to open or close it.

Do you have a scanner? Have you checked how the PCM is trying to modify the IAC "counts" to control the idle speed?

Daniel6718

havent had time to check it but i checked the cruise linkage and loosened it and it seemed to help some...but is it normal to pump the brakes and have it idle up 3-400 som?

Daniel6718

injuneer i checked it and it was 48 for both...and the other 2 were open leads like they needed to be...any other ideas?

Injuneer

Have you checked for a vacuum leak in the hose that runs from the intake manifold to the brake booster? Also the connection on the booster? Try pulling the hose off, and plugging the brake booster connection at the manifold (remember, you will have to push harder on the brakes to stop ). See if the problem goes away. That would confirm a vacuum leak in the brake booster line or the booster itself.

Daniel6718

i have checked the hose to the booster...the 90 degree elbow....


ill plug it and drive and see what it does thanks....report back soon

Daniel6718

its worst when i drive the car a short distance i can drive along in 5th at 1400-1500 rpm then slow to take a turn or stop and push in the clutch and it goes to maybe 1800-2000...and will stay...i can sit at a light for 15 seconds and it still stay at 1500-2000rpm whatever and slowly come back down to 900


i mean i know when you have it tuned for a cam it will idle at 1600-1800-2000 wen you slow down...thats understandable....but does it also do that on a non tuned stock pcm

jchevy

My car has just recentley started doing this, havent put my scanner on it yet, just subscribing to the thread for now.

We have the EXACT same problem