aklim

Where did they get 8 degrees from? Thought it was 6?

Have you begged, borrowed or stolen a scanner yet? Lets see what the desired idle speed is from the ECM.

Better mechanic?

Dunno but I'd lend you mine if I didn't already sell it away. I'll bet it doesn't though.

Sometimes a shop will replace the TB with one they found in a pile because the customer wanted cheap or the customer brought in one to place in the car. All hard to say.

Cajaw Jordan

I was quoting from the mechanics notes.....i could fax you a copy if you would like to see.....i think they ran a scan...i will try to get someone to scan the notes and then upload the notes to my computers.....anyway...i will be taking the throttle body to the guy who did the troubleshoot and have him show me how it is modified. The poor guy behind the counter will probably catch hell....as I don't believe he was supposed to give me those mechanics notes...they are for the shop only and personal....they derive the bill from these notes...They did do alot of work on this car and charged me a fair price......but i am very suspicious about how good this ace(supposedly) mechanic was.......personally i think i could have done better myself. thus i am replacing the injectors, than rechecking vacuum, and fuel and oil pressures. Would you try to replace this with and OEM TB? as i stated before i tried the idle adjust procedure with the IAC... .54vdc .....the screw adjustment does nothing turning it in all the way in or out...whats with that?......LOL:craz y:

Cajaw Jordan

so what actually controls idle speed.....i can relate to a flow chart....starting with ECM, maf, tps, iac, i am used to my old dodge (65 coronet poly 4dr which starts and runs great and could be and everyday driver)......where you just turn a screw and tada! lol.....

aklim

If it is 8 degrees, someone has some explaining to do if the standard is 6.

I doubt he is that good.

I wouldn't. Without seeing what the count is when totally warmed up with all accessories off, I am not sure.

MrWillys

The ECM controls the idle! Most stock L98's fully warmed should idle at about 600 rpm. The throttle blade works in conjunction with the IAC to keep the car at the called for idle by the ECM. A surging idle is usually something wrong like bad injectors, or a bad device reporting poor information the ECM makes decisions on. Get the new injectors in, and maybe a picture of said aftermarket throttlebody. I think new injectors will help your condition.

aklim

ECM controlls it. Hence the "Desired Idle Speed" or "Command Idle" or whatever it is called. ECM wants say 1000 rpm and it will try to do it via the IAC which is a metered air leak.

This is why I said setting it without knowing what it is trying to do is very difficult unless you are stock. You set it the GM way which is perfectly valid and if the desired idle is not what stock it, it could be difficult. ECM says it wants 1000 rpm and you set it to 500 and it will try to open the IAC to compensate and might not be able to

aklim

I'm still suspicious that the chip is alterd though. If the desired rpm is not 600, I am not sure the GM way of setting is going to work, is it?

BTW, what is the standard timing? Isn't it 6 degrees?

Cajaw Jordan

i am not sure of the desired firing angle but will go to the service manual and look it up. the mechanic did switch out the ecm and found no difference. one of things that was really strange is the maf, i had bought one at autozone early on and it didn't make a difference...no codes ever popped up....the mechanic also tried a new maf and exchanged the maf burner/relay(?) finally a code 33 popped up....bad maf....a new one was tried and the car ran and started well......but...next they tried to set the idle and could not get it to run smoothly...this is the end of the note that says idle could not be set due to modified tb....You seem to have taken and interest in this car and you, like myself, love to solve puzzles it seems. I was the "go to guy" when i worked in the Steel mills as and electrical/mechanical/electronics/hydraulics/pneumatics technician and then as a charge RN at the VA Hospital with only a few years experience. I will not rest until I find the answer on this car...lol....my saying always has been..."There is a solution to every problem if you look and work hard enough to find it." My younger son does not understand why I will not give up on this car.......he would junk it or sell it....The younger generation just does not get it......solving what seems to be and unsolvable problem..gives you a real sense of achievement and I will solve this mystery no matter what!

MrWillys

I'm not sure I understand what you mean in the first 2 sentences? Fully warmed with a scanner it should show "desired idle". Any good programmer wouldn't raise stock idle on a stock car? Pull the memcal and see if the oem bcc sticker is on it?

Base timing for all L98's is programmed based on 6 degrees initial.

Cajaw Jordan

thank you mr *****!
i will wait until i get this car back together in a week....hopefully the injectors were bad...looked like crap on the outside but who knows? i just had skin surgery today for basal cell cancer and was told not to go near that car for a week due to 3 layers of stitches! i feel as though someone hit me with and aluminum baseball bat right beneath right shoulder blade.....lol.....i will tune up my 2000 hondog civic...my go to car..lol....finest piece of engineering that i measure every car against!... not crazy about japanese cars.....but the KISS engineering is beautiful! and 40.5 mpg at 70-85mph on a 400+ mile round trip to the mountains last week....! and i discovered the car has never been tuned in 150k and only part failure was a o2 sensor last year....son admitted to me he did nothing but change oil in 10 years he drove it.......grrr.......lol

mtwoolford

"When you eliminate all the logical solutions, what remains, no matter how illogical, must be the solution" I think I read that in an Agatha Christie mystery novel....or could it have been the Factory Service Manual ? Get well soon

aklim

You would be right about any good programer. However, I have see idiots try to do silly things. This includes someone sticking a larger than recommended NOS system on a 90s Ford Taurus SHO and toasting the engine and freezing the manifold at the same time. I had a garage try to get into programming EPROMs when he didn't even understand that you have to disconnect the tan wire to set timing. He wanted to me to teach him how to set it up so he could make money tuning.

Kinda what I thought.

Cliff Harris

One of the side effects of looking at a problem REAL HARD is that you learn a lot!

You spend a lot of time saying, "What exactly does the X do? How does the Y work?", etc.

"Builds character" as a co-worker used to say...

Cajaw Jordan

Mtwoolford,
The original idea for my philosphy is....Occam's razor (also written as Ockham's razor from William of Ockham, and in Latin lex parsimoniae) is a principle of parsimony, economy, or succinctness used in logic and problem-solving. It states that among competing hypotheses, the hypothesis with the fewest assumptions should be selected. In other words, the simplest explanation is usually the correct one. LOL>......sounds like a plant to me!

Cajaw Jordan

plan not plant....i am up to early! and no coffee yet! ah yiya!

Cajaw Jordan

finally found my micrometer.....bore is 52mm...original supposedly 48mm.....would this throw idle out of whack? will continue on monday putting vehicle back together with new injectors......fire it up and see what happens.....hopefully i can start tugging and fighting this car with about 40 stitches under my right shoulder blade.....that surgeon tore me up! we shall see.....48mm bore vs 52 less than 10% increase in bore size....could this cause all this idle problem? is the PROM that intolerant of such a small change.......what would you gain in HP with a 4mm increase in bore size....or is 4mm X2......does not seem like much.......but..........??????????????? i also see a gap of probably less than 1mm with butterflies closed.....could that be construed as a vacuum leak........i need a beer!

JimGnitecki

Going from a 48 mm cross-section opening to a 52mm one is MUCH MORE than 10%, because the area of a circle (i.e. the cross-section of the bore) goes up as the SQUARE of the radius! That means a 52mm bore is 17% larger cross-seciton than a 48.

Furthermore, the CIRCUMFERENCE of a throttle opening that is 52 mm versus 48 is, as you say also 10% "longer', so the same width "gap" between the throttle blade and the body is going to pass 10% more air, even without the square factor above.

The two combined effects would potentially be pretty significant.

Jim G

Cajaw Jordan

funny, but reading these forums and trying different ideas.......and talking to chevrolet techs.....i realize.......they really don't know ****.....i can honestly state...that if i were a chevrolet tech......i would know every chevy ever made and have notes, and people i could call to solve any problem....it is why i am insane......the younger generation.....i have sons 31 and 27 who have no interest in deep troubleshooting.....anyone i know who knows cars started as shade tree mechanics......and can just about fix anything.....i see very few if any younger guys getting into extensive auto repair.....they are more interested in sub-woofers and usb ports and backup cameras.....we are becoming a country of unskilled labor.........sadly! kids would rather work at mcdonalds than get their hands dirty. Just my opinion.....but echoed by most enthusiast in my age group...

Cliff Harris

There is supposed to be a gap. You need to do a "minimum idle adjustment" to get that gap to where it should be. Here's the procedure:

http://forums.corvetteforum.com/1570563689-post1.html

aklim

Wifey doesn't think that is a good idea. There again, she has a husband that removed the injectors from 2 Seadoos within 2 weeks of getting an elbow tendon re-attached and a bicep and rotator cuff thingy getting done. Of course she thinks I am stupid but I am smarter than that. I didn't tell her till a couple months later.

Forget it. You won't gain much if the engine cannot use the air. Also, you don't have a 90 or 91 so you have a Mass Air system as opposed to the 90-91 Speed Density so it should adjust better.

Of course that is a "leak". So is the IAC. That can be called a crude calculated leak while the IAC is a more fine tuned "leak". Say your desired idle is 500, the butterflies leak enough air for 400 and the IAC gives you enough total "leak" to achieve 500. Depending on conditions, the ECM might command 400 or 600. The butterflies cannot adjust so the IAC adjusts to give you the extra 100 or lower it by 100. BTW those are just numbers for demonstration but you get the idea. So if you set the butterflies at 500, all is well when the ECM decides to set the commanded idle to 500. However, what if it needs to lower it to 400? It cannot. This is why I prefer to set the idle speed via IAC counts. I set it to say 30 counts so it can increase if needed and lower it if needed.