Jachin99

I just bought this car and this code appeared the other day. as far as i know the only mods that have been done to it so far are a slp maf sensor and aftermarket exhaust. i know the dealer also cleaned it real quick before they handed me the keys but other than that i havent done any work to it. it has a small miss at idle but other than that i havent had any problems with it. what could be causing this? thanx

2001NBMZ28

99? www.gearchatter.com/viewtopic8841.php

Jachin99

I dont have a scan tool and the code goes away in colder weather. i think this weekend im gunna put a tune up on it, including a new pcv valve and possibly clean the throttle body and check for vacume leaks. how would i check for vacume leaks? i have heard of people using fuel injection cleaner to do it but im not sure how to do that. Would i need to get a new tb gasket if i wanted to take it off and clean it and where is the pcv valve located?

Injuneer

You might want to add some basic info about your car, including year, model, engine, tranny and any major mods. Makes it easier for people to help you and answer your questions. Codes are often unique to a specific engine family, or to specific years of specific engine setups.

Why not use the "signature" option?

Jachin99

signature added

Jachin99

i replaced the pcv vlave and cleaned the housing. im not sure how much sludge should be in there but it looked like quite a bit to me. the old one was still good but i replaced it anyway. i also removed and cleaned the iac valve and i cleaned inside the iac housing and the tb and cleaned the tb outside of the butterfly. and i checked for airway obstructions and found none. it just idles a little higher now at around 1000 rpms half the time and it still has the code. im going to check for vacume leaks next but ive never worked on a vacume system before. i checked under the hood but i couldnt find any obvious vacume hoses other than the pcv system. where should i start to check for vacume leaks? thanx

Jachin99

any help guys any other places to check for vacume leaks aside from pcv system and around intake manifold?

bobdec

Here is what I can think of anyone else can chime in if I missed anything. Fast idle is due to more air entering the manifold than the computer commands thru the IAC. Air can enter through the following places --- 1- intake manifold around the block, bad intake gasket which is rare and only effects specific cylinders unless work was done incorrectly by someone, check the torque on the intake bolts, spray starting fluid around seams to test. 2- OPTI vent line under the TB, plug and test. 3- vac line to the fuel pressure regulator, plug and test & sniff for fuel in line. 4- vac form TB to PVC , plug and test. 5- vac hose to power brake booster, plug and check. 5 - vac line to the EGR valve, plug and check. 6- vac line to the HVAC system, plug and check. 7 - IAC stuck open, you already checked this out (sludge comes from EGR exhaust crap). 8 - TB butterfly stuck open, visual check of linkage. 9- TB stop setscrew cranked to far, check TPS voltage. Engine will also run fast if temp sensor to the PCM thinks it cold or engine goes to survival mode, but since you are throwing P0507 those causes can be ruled out.

Jachin99

So i got out the can of ether today and started spraying around the engine compartment and noticed that when i sprayed around the iac valve, the engine revved up and thats when it clicked to me that when i took the valve off to clean it there wasnt an o-ring or a gasket there. So my question goes as follows; is there supposed to be something there that seals it up and if so could i purchase it seperately or would i have to buy a new valve entirely. if there isnt anything thats supposed to be there, how would i fix the leak?

bobdec

Sorry can't help, I had my '94 IAC off about a year ago, but it's not the same as the '96... Now that you know the problem, maybe reposting under the engine section would get someone's attention...

Injuneer

He has a 99. Comments #2 (Opti vent line, which BTW does not connect under the TB), and #3 (vacuum line to FPR) are specific to the LT1 and do not apply to the LS1.

Jachin99

Ok the code is still there. Here is what ive done so far.

1. Installed new Oring and IAC valve, checked area for leaks and found none.

2. removed TPS sensor and inspected Oring for any sign of damage, reinstalled, and checked for leaks. found none.

3. Pluged vacuum line coming out of throttle body to check pcv system and brake system for vacuum leaks. found none.

4. I can eliminate the A/c system because it only
draws vacuum when it is turned on, and the idle goes down and the code goes away with the a/c on, Im assuming because of the extra load on the engine.

5.I have tried just clearing the code, and it comes back every time and still idles around 800 RPMs.

6.I have cleaned the throttlebody and replaced the pcv valve, however i have noticed that a small amount of oil is making it past the pcv valve

7.I have sprayed all over the engine in every conceivable spot to try and find some random vacuum leak and have found none

From all of this i can eliminate the iac valve itself, and any vacuum leak coming from anywhere, assuming that the one vacuum line coming out of the throttlebody feeding the pcv and ac systems is the only spot tapped into the engine that provides vacuum for everything. The only thing that i can think of that could be wrong now are the ECM or the harness going from the valve to the ecm. How do i check those?

Jachin99

I checked the wiring to the ecm by disconnecting the harness at the IAC valve and ecm and the battery. I checked the wires for the IAC low grounds for both coils and they were both really close to just 1 ohm. Is that normal and can i just swap a new ecm off the shelf from autozone to test it?

Jachin99

And Isnt there supposed to be a cover on the ecm?

Klypto

i think i had that code when i missfired