Throttle Body Gasket?

[shultzee13]

I have a old body style 5.7L Vortec Suburban. C1500 2WD. Idle is erratic when braking and AC is on. Have basically rebuilt truck. All new O2 sensors. New TPS. New IAC. New fuel filter. New fuel pump. Live data on code reader shows no trouble codes whatsoever. Runs great except under these conditions. I cleaned the throttle body itself about a year ago, but I did not replace the throttle body gasket. I don't hear any hissing anywhere except around the PCV valve on the valve cover grommet. I've fought this for 6 months.
I did install a new brake booster as well. No change. Both Cats replaced less than 3 months ago.
I have no codes or lights on. The EGR valve is dirty but according to scan tool is working fine. Can parts wear out and just not throw a code?

Thanks Guys
I need some help

[68c10airstream]

I'm assuming your truck is a 1996 and newer 5.7. If your truck is stock and basically unaltered here I go, Ecm can't see the idle speed motor so it uses stepper motor counts to reference it's placement. As you drive 45 mph and higher the ecm fully extends the iac motor to fully seat it, then retracts it the prescribed amount based on application (a/c, no a/c at, or manual, etc, etc,) So the ecm constantly recalibrates the iac position. If you can get to a scan tool your iac position is usually around the teens for value, say 13 iac counts. As an example If by chance your minimum idle speed screw was backed out (throttle closed too much) the iac would compensate for this and iac counts would be higher say 20-25. If you had a vacuum leak iac would be zero or near zero and idle speed would be above target idle value. Now a little more in idle speed control info is this (just for the sake of info) iac motor steps (counts) are a rough adjustment and the ecm fine tunes it to get as close as it can by adjusting timing advance up or down as needed. Did you check base timing and go by the proper procedure for this?? If everything is normal i suspect a slow closing egr valve. Seen it a few times, remove it and clean it using carb cleaner and compressed air. If the egr is pointing up towards the front of the motor and has an electrical connection they seem to get dirty and be slow to respond closed, but rare. If the egr is at the back of the throttle body (throttle body injection-tbi) I have had more problems with those. If it's this style , remove it clean it with carb cleaner and compressed air and then record the gm 8 digit number and pay special attention to the letter after the 8 digits. Is it a "P" or an "N"?? 2 different operating egr valves based on the letter. When the egr is removed before you re-install it start the truck up (you may have to floor it) and rev it up pretty good to blow out the carbon in the intake manifold passage ways. I've probably flooded your brain, but now you have in print what to do. Good luck, Brian F.

[shultzee13]

It is a 99 C1500 Suburban 5.7L Old body style

[shultzee13]

It was idling too low about a year ago and a local mechanic turned up the adjustment screw on the throttle body. At normal idle just sitting still after I crank it, It is 500 maybe 700 RPM

[speedygonzales]

Your mechanic is an idiot.

How many miles on it?

You never mentioned the EGR. After a lot of miles, the pintle on the EGR will never close and effects the idle. ?????????

Have you ever checked the fuel pressure, or considered a new spider assembly?

And the TB uses a shaped O-ring not a gasket. If you suspect it's a problem spray some thick lube around the base of TB while it's running.

[shultzee13]

The EGR looks original. LOL. The fuel pressure was checked and is properly functioning. The EGR has been taken off and cleaned, and it's not throwing a code so I didn't suspect it.
190,000

[shultzee13]

[QUOTE=speedygonzales;7199610]Your mechanic is an idiot. I am finding a lot of so called mechanics are idiots on these engines.

[68c10airstream]

I should add that the ignition timing check only applies to tbi engines, not vortec engines. 5.7 vortec engines have an adjustable cam sensor built into the distributor, but ignition timing is not adjustable. There is a system check that looks at the sync signal between cam/crank and because of wear of timing chain, gears, cam gear, etc, the cam/crank will be out of sync and you would then adjust distributor body (cam sensor) to get it back in sync. It would usually be a case of the cam trailing it's normal position because of wear and you would advance the distributor to get the scan tool to show near 0 degree if i remember correctly as i only did it a couple of times in the late 90's. Another item to look at is the mass air flow sensor. The sensor is in the airstream of air entering the engine between air filter and throttle body. The mass air flow sensor gets dirty (especially if you use a K&N filter, which i hate) and it skews the sensor to be richer that what it normally would be at low rpm's and be leaner than what it normally would be at higher rpm's. If you remove the sensor from the ductwork, pay attention which way it goes in because it is direction sensitive and they usually have a arrow marked on the body to indicate airflow direction. Now for cleaning; get a can of electronic contact cleaner, or better yet get specific mass air flow sensor cleaner and spray the incoming side of the sensor, holding the sensor in your hand the same position as it is installed in the car. Another words the wires plug into the sensor at the top so maintain that in the up position as you blast the cleaner at the inner core of the sensor. You don't want it upside down and have the cleaner run inside the sensor's module built inside of it. You will see 3 shiny stems (heavy wire) holding what looks like 2 little pills bridged across the 3 stems. Clean it repeatedly until shiny. The backside is almost always shiny but the incoming side gets dirty because no air filter is 100% efficient so a little dust goes through and impales the dust on the face of the resistors (pills). If you are running an aftermarket free flowing air filter (i like to think of them as bug screens with gooey oil spread across them) you will need to clean it about every 3-6 months for peak mileage/performance.

[shultzee13]

I cleaned the MAF sensor about a year ago. If it was dirty would it signal a code? I bought a new EGR valve tonight and to be honest the plunger might have a little more play than the new one but not much. I am tempted to return it and just put the old one back on. After all it was $120.00
I did notice the EGR passages are black with carbon. Will have to google how to clean effectively. Vacuum perhaps?

Not sure how to tell if the new EGR will make a difference. I'll buy some MAF cleaner as well and report back.

Maybe it's just a 99 - 15 yr. old Car. Kinda bummed I can't figure it out.

[68c10airstream]

As speedygonzales stated the egr may be leaking. My easy go to test is this; start up the engine cold (overnight) and DO NOT TOUCH THE GAS PEDAL, as the engine warms up feel the base of the egr. If it's getting warm exhaust gas is leaking past the seat (not sealed up completely) and then remove it and clean it. I believe (without checking) that the egr style on your engine has a built in pintle positioner sensor and if it's off the seat it would display it on the scan tool in percentage open, i think. At idle it should be 0% open. I'm having to stir the gray matter on this from my gmc dealer mechanic days, breathing carbon monoxide, poorly lit shop, poor ventilation, and inadequate heating, but i liked the challenge

[68c10airstream]

Vacuum the passageways??? use my suggestion of starting the engine and reving it up to clean them out. Vortec 4.3 v6's that burnt a little oil had hard carbon chunks that held the egr open. My boss came up with a stainless screen siliconed between 2 base gaskets that cured overnight, then installed to try to stop the chunks from getting stuck in the egr. I came up with the procedure of starting up the engine (may have to floor it ) and rev it up with the egr removed. Black smoke will shoot out and possible chunks of carbon. A dirty mass usually does NOT set codes.

[68c10airstream]

If after all of this as a very slim chance your engine controller (pcm) could have a iac driver circuit failure and it doesn't set codes. I will instruct you on how to make a iac tester with resistors and diodes and gut an old iac motor out to get the plug in end to solder these diodes and resistors and then plug it in, start truck up, rev up and down and see if all of the led's switch colors (red/green) to verify if the circuitry is switching polarity back and forth to simulate an idle up and an idle down electrically.

[shultzee13]

Getting 12v at the EGR. Revved it up no chunks flying out. It appears passages are black but not clogged. Not sure EGR is my problem after all.
IAC is less than 6 months old. I can tell you the EGR valve getting freaking HOT when vehicle running. Cant touch it until car cools down. Gasket looks good. Not cracked or torn.

[speedygonzales]

Many items will not throw a code so don't expect OBDII to be the answer to your problems.

68c10 when you type can you use paragraphs. I can't read your long winded replies it hurts to look at them

Voltage at device does always mean anything. In this case remember, the EGR is to work only when the engine is above idle. So you should be scratching your head right now if you checked it at idle and see 12 volts there. By your thinking, it should be open.

Many devices are operated with a switched ground. For example the fuel injectors. You would see 12 volts there all the time. When they are turned on, they are given ground.
Understand?

I personally think you should measure 2 things. Intake vacuum level and crankcase vacuum level.

Just for giggles you could pull a hose off the intake and see if it effects the idle quality. If it doesn't, you probably have a leak.

Same with the crankcase vacuum level. Most people don't even realize the crankcase is under a vacuum. A small one compared to intake vacuum but a vacuum none the less.

[68c10airstream]

speedygonzales, I don't do much on the computer and my skills are poor to say the least. So tell me how to do paragraphs?? I move the cursor but it won't stay there when I enter it. Asked 2 co-workers but no time for me to teach me, but come to me to fix their cars! I'm 58 years old with a head full of repair knowledge so you can beat me up for the long winded replies but at least you didn't find fault with the info. Have a nice day, Brian F.

[speedygonzales]

You don't move the cursor. You simply
Hit
the
enter
key
the one with the arrow on the right above the shift to the right of the " key
to start a new paragraph.........try it

Then when you have the writing split into legible paragraphs
You put the cursor on the "post quick reply" button and press the mouse left button to post.

If you took some sort of offense ????? to what I said perhaps you should take a deeper look at yourself. I merely wanted to read what you wrote but like many others I'm sure, it was difficult. So I chose to just not do so. The use of the enter key is really simple. I'm sorry that you obviously didn't know to use it. I hope you have a good day!?

[68c10airstream]

Originally Posted by speedygonzales

You don't move the cursor. You simply
Hit
the
enter
key
the one with the arrow on the right above the shift to the right of the " key
to start a new paragraph.........try it

Then when you have the writing split into legible paragraphs
You put the cursor on the "post quick reply" button and press the mouse left button to post.

If you took some sort of offense ????? to what I said perhaps you should take a deeper look at yourself. I merely wanted to read what you wrote but like many others I'm sure, it was difficult. So I chose to just not do so. The use of the enter key is really simple. I'm sorry that you obviously didn't know to use it. I hope you have a good day!?

"Take a deeper look at yourself"?? If you only knew what I have done with family relations in the last year to stop 60 years worth of issues!!
This is now going in the wrong direction from the initial thread post and from here it will probably not be in the best, so I will bow out of this now!!!

[shultzee13]

I appreciate both you guys! I cleaned the throttle body today. I also believe that some bone head mechanic installed my MAF sensor backwards. I corrected that as well. Will report back how it runs with the AC on.
Again I really appreciate BOTH of you for your help and patience. I am a little bit knowledgable on the 5.7L Vortec but I always come here for the real experienced people.

Both of you be blessed.
Shultzee