If you intend on cleaning the TB, I would unbolt it from the plenum and give it a good cleaning. By leaving it on there you want be able to clean it as well and I had a hell of a time removing the IAC while the TB is attached. When you remove the IAC, check the gasket. It becomes very brittle and will break. I had a time finding a gasket for it and none of the autoparts stores carried it. You might be able to get one from you locate Chevy dealer. If you replace the TB gasket make sure it is the correct one because you will get two in the pack when you go to get one. I just bought a new IAC and it came with a gasket. Clean that bugger good and also in the air passages as well. I used a old toothbrush and a small bottle brush to get into the small areas along with your choice of TB/carb cleaner. When installing the IAC make sure the tip of the pintle is no further than 1/8" from the flange. Also when I bought my vette someone had installed a air foil and the small U shaped area at the bottom is suppost to let air flow to the IAC, but after removing the air foil my idle improved a lot. It seems that you have a air problem to me, after reading the thread.

Although tapping the fuel guage to you windshield might show you something. The EGR valve is hard to see, and make sure the solenoid is getting vacuum. The EGR system is only active at highway speeds and acceleration...not idle or WOT.

thanks for the reply. i seem to recall that, when i sprayed/cleaned the tb out a few months ago, it made a difference w/o removing the tb. i will try that first to see any difference.

i am aware of the gaskets being brittle. it is locating them that is gonna suck!..i also tried some months ago to remove the iac but, could not get at it because of the tb being in the way. that is whay i sprayed into it instead of removing it. are teh gaskets for the tb available in parts stores?

i have printed out the proceedures for cleaning the iac but, with no gaskets right now, that is not an option....

will tape fp gauge as i had planned, onto windshield and see what happens.

right now i am looking for my patch cord to the computer for my "x-ray".when you say that "The EGR system is only active at highway speeds and acceleration...not idle or WOT", are you saying that it does not "come into play" when accellerating from a standing start?

The only way I found "good" to clean the TB/IAC is removing it. I did clean it still attatched but after removing, I found areas that were still carbon filled and were much easier to get to after the TB was off. The IAC and gasket cause about $30, but I think GM sells just the gasket, but not positive. You can go to the autoparts store and get some gasket material and make your own gasket with a little cutting. The TB gaskets can be gotten at just about any autoparts store for < $5.

Vader86 explains the EGR function pretty well.
http://temp.corvetteforum.net/c4/vader86/egr.html

Did I read that wrong RRT, isn't the pintle supposed to be out no more than 1 & 1/8 inches from the flange, you said 1/8? Maybe I should check, but I think it's 1 1/8.

You are correct, didn't read back through.

ok.......update........i cleaned tb like i said due to the non-availability of gaskets at this time and it maybe runs a bit better at idle but, falls on it's face still. i checked fuel pressure again and is ok and vacuum is
161/2 - 17. ok, now is the "funny part".

i have 2 maf's, the orig that was on my car when i bought it and another i obtained.

i took off the orig and tested the one i have been running with for about a year now with no problems. both test/tested to be good.

ok, i unplug the maf and the car DOES NOT STUMBLE any more (codes of couse!) . but wait!, i did this (unplugging) with BOTH the two maf's i have and the car DOES NOT STUMBLE!

this is strange because the orig i took off was good and properly stored. how now can both check to be bad or at fault? is the maf connected anywhere else other then the ecm? i am not saying it is impossible but, at the same time?....no dirty connectors or broken wires..

forgot...did you check the connections at the ECM? by disconnecting the MAF,and noting an improvement it would typically indicate a bad MAF, unless one of the relays or connections were bad.Before I replaced a MAF...about $180 for a rebuilt I'd check everything else. And if your sure the stored MAF was good...well, time to trouble shoot the circuitry.

have not ck'ed connections at ecm yet.....damn hot down here in florida, may have to wait until tomorrow. yes, i am aware that unplugging the maf and car running better is sign of bad maf but, both maf's at same time?..ugh!...i have replaced maf relay and i have also no codes to indicate it. i will unplug the maf relay and re-connect it although, i think it not the problem.

i have just finished running a scan with car idling in driveway and then shifting in reverse but, can't figure how to post it here. i should have taken a scan with the maf disconnected too.

When you unplugged the MAF, the ECM used default settings. Apparently the MAF(s) were sending a too low a signal (g/sec). Since you didn't have a code with either MAF sensors, you might have a weak circuit. Use the FSM and test the signal wire (green I think) at the ECM to see what the voltage is. At least were not guessing anymore and have narrowed it down.

send me a pm with your e-mail address....i would like to send you a few picts of the data since i cannot transfer them to a word doc, or so it seems.......

.......picts as attachments sent via e-mail.....will try to find way to post on forum....thanks!

ok......forgot how to do this but, lets see how they come out!

There are a few things I'd have to look up like injector pulse, but the MAF looks right, should read between 4-7, the IAC steps, hmmmmmm, thought they should read 1-40? BLMs 118-138, so I guess your close.I going to post something about a back pressure guage, and for the life of me I can't remember what the vacumn should read, I only bring that up because I thought your might be low.

THANKS for the reply........don't think it is a back-pressure problem.......car was running fine before this crapola and seems to run fine with the maf disconnected.........wouldn't the car still run like "dung" if there was a back pressure problem with and without the maf's connected/disconnected?

is there any more info that needs to be posted as this scanner "can read palms"!....grin

PS....the car was running in park and then i shifted into reverse with foot on brake..if that answers the huge spike in the graph...

From what I can tell, everything looks to be normal. It's giving you a rich flag and the BLM's are 140 which is lean. But this is a freeze of just one instance. The MAF signal is appropriate for the idle RPM. Are either one or both of the MAF descreened?

thanks for the reply...no descreening here!.......the vacuum was also as steady as a brain surgeon's hand so, i doubt vacuum leak anyway.....i will remove ecm tomorrow and check connections. as for me, i am spent on this thing for two days in the heat!....will like to bounce thoughts and comments around the forum for a while.........someone mentioned "a weak signal" test to the ecm....synopsis on how that test is run?

yea, positive maf stored was good sir.

I'm at work and don't have my FSM, but you can look through it and see which wires run to the MAF and where they are located on the ECM connector. It also tells you, in there, what they are and what they do....ground, signal, ect..

The dark green wire (on my 86) is the signal wire and should test 5v with a voltmeter. You will need a voltmeter and a test light.

Think that was RRT regarding a voltage check to the ECM, and I think he was referring to a green wire, it's in your FSM. I just can't remember what vac. readings are supposed to be at idle, and I can't seem to find them. The back pressure gauge is used to determine if the exhaust is restricted (cats), that's why I mentioned it, don't mean to get you off track..it was just a thought, cause plugged cats can make a car drop on it's face in a heart beat.

At least now you know what is causing the problem, hopefully. Just testing the MAF and relays circuitry is needed.