another idle problem..... low vacuum at idle in gear.

[5678TA]

Ok guys so i've been chasing idle and lean demons since my MAP sensor went down couple weeks ago. I've since replaced the MAP and IAC and now my problem is this:

When in gear, idling and at a stop, vacuum goes anywhere between 12 and 17. Out of gear it will idle at 19 or 20 vacuum. As per reading from my Truboost gauge. I notice that when in gear, the wideband goes waaaayyyy lean. I'm talking anywhere between 16:1 and past 18:1. Occasionally stalling as i'm slowing down to a stop. When vacuum is low at idle, i'll tip in the throttle and see the vacuum actually increase and then decrease. Example: idle is 13ish vacuum, then tip in throttle, 14,15,16,17,16,15,14,13,12,11,10 and so on.... Another thing, when i'm in this situation and then suddenly put it in neutral, i see the wideband spike rich and come back down to normal A/F ratios.

Datamaster says throttle is closed, or 0%. My questions is what could be causing a relief of vacuum when i'm idling in gear??? It's obviously taking in more air then it should be while in gear at idle and at a stop.

I used to be normal with 19-20 vacuum in gear. I'm stumped.

 

[Eric Sy GN]

Re: another idle problem..... low vacuum at idle in gear.

What do your IAC numbers look like at idle? With the truck warmed up, in park, it should be somewhere around 10-30. The reason I ask is the Velosyty chip looks at the IAC when doing idle fuel calculations.
If you want, email me a log (or post one here).

Regards,
Eric

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

Eric,

I did an ECM fuse pull to try reset the IAC. Here is a quick drive.

http://www.mediafire.com/?p1r2decyx314wvb

Today, vacuum was keeping around 16-17 in gear at a stop. Still leaning out to a near stall when coming down from speed. Takes about 10 seconds for the A/F mixture to come back up to around 15:1 which is weird because yesterday it would stay lean at idle.

The datalog was done on the way to the store. When i got back, IAC was 0 in park but A/F still managed to wiggle its way to 15:1 after a short wait. I'm hoping the updated eprom you're sending me fixes the problem.

If there is a specific driving scenario you want me to log, let me know and i'll get that logged.

 

[Eric Sy GN]

Re: another idle problem..... low vacuum at idle in gear.

I'll look over the file. However, with the IAC at 0, it will contribute to these problems. If the IAC is closed (at 0), that means the engine is getting air from somewhere else in order to idle. It could be a vac leak, PCV problem, or maybe the throttle plate is not closing enough when closed. There is a throttle stop adjustment on the throttle body that allows you to adjust the throttle blade closed position.
Maybe the new IAC is slightly different than the old one. I've seen some aftermarket ones that needed the pintle length adjusted before install.
Regards,
Eric

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

Thanks Eric,

i'll go through the topend and see what i can find.

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

did a leak down test with an electric tire pump. (dont have a compressor, weak i know...) regardless of the extremely low cfm output, i could hear a hissing coming from around the throttle body shaft, possibly lower. replaced the PCV hose, valve and throttle body gasket. still runs lean.

i'll try the IAC gasket tomorrow. think my throttle plate shaft could be leaking that bad? this only started after the Meth kit was installed. meth possibly cleaned the gunk sealing the worn out shaft??

everything but idle is fine. still responsive, shifts fine, power is still there.

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

Got a set of intake manifold gaskets and ordered a plenum gasket.

I suspect an internal lower manifold gasket leak since i did the carb cleaner leak test and came up with nothing. So we shall see.

 

[Flyin Ryan]

Re: another idle problem..... low vacuum at idle in gear.

I remember years ago Ed Hess had idle issues and chased it down eventually to a beat lower intake gasket when he started tearing into it to upgrade

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

I remember years ago Ed Hess had idle issues and chased it down eventually to a beat lower intake gasket when he started tearing into it to upgrade

Ya, i read a few posts about Ed Hess's issue doing a ton of searching on here. Figured i give it a shot since the carb cleaner didnt uncover any leaks. I sure hope it fixes the problem. will post my results when i get around to pulling the intake.

i suppose i could pull the plugs and look for significant oil residue. but regardless, the intake is coming off.

 

[Flyin Ryan]

Re: another idle problem..... low vacuum at idle in gear.

Ya, i read a few posts about Ed Hess's issue doing a ton of searching on here. Figured i give it a shot since the carb cleaner didnt uncover any leaks. I sure hope it fixes the problem. will post my results when i get around to pulling the intake.

i suppose i could pull the plugs and look for significant oil residue. but regardless, the intake is coming off.

I know our throttle bodies are known to leak but maybe yours is at the point where it needs to be reworked or replaced? I couldn't even suggest how you could test the tb though

Good luck and post back what your findings are with that lower intake please

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

I know our throttle bodies are known to leak but maybe yours is at the point where it needs to be reworked or replaced? I couldn't even suggest how you could test the tb though

Good luck and post back what your findings are with that lower intake please

Thanks. and will post results. give me a week or so... plenum gasket is on order.

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

Got the manifold off and im pretty sure #6 was leaking from the inside. There was a nice film of oil all over the lower part of the gasket and the bolt was oil soaked. Time for work so ill finish up tomorrow and let you folks know what happens.

And as far as the film of oil goes, it had a different "pattern" than the other cylinders where you could see where the gasket made a nice seal.

Picture of oil from bolt and side/bottom of #6

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

F me.... Still going lean. Its stalling now too... Could be because I eyeballed the timing but nonetheless, still lean. Anybody got a cheap, good tb for sale?

 

[Eric Sy GN]

Re: another idle problem..... low vacuum at idle in gear.

If the IAC # is still hanging down on 00, then you might try adjusting the throttle stop. You would need to unscrew it a little bit, so the throttle closes up. As you close the the throttle blade, the RPM should drop and that "should" force the IAC to open up to control the idle. Try to get it up around 20 or so. I think it's a torx screw, not sure what size.
Eric

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

Eric, I adjusted the throttle stop and iac went up. Shes still jumping around as far as the a/f ratio goes. Its mainly staying around 15:1 but will jump to 15.6,15.7 then to 14.3, 14.2.

its lunch time so ill go for a drive around my parking lot later and see what happens. I just want her to purr again... Then I need to get my buddys timing light. I can tell its off. Theres a slight rpm float.

 

[Chest Rockwell]

Re: another idle problem..... low vacuum at idle in gear.

I can send you my throttle body. There's some shaft play, and you'd have to swap IAC and TPS, but it's free if you want to cover the shipping. Also needs new gaskets. I took it apart to clean passages, and haven't finished yet.

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

well guys, i have other problems now. damn starter went out. also after i adjusted the throttle blades, now she wont idle when cold and then i readjusted and she went 10:1 rich then idled at 1800 then now hovering around 1200. I just want to say, I love carburetors.

Steve,
i'll hold off for now. i wanna get the starter dealt with first.

Then i'll hit up the old shop i used to work at and do the bike tube test again but with their smoke machine and a real compressor. Who knows, it might be something else. I HAVE NO F-ING IDEA!

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

Look what I found... Charcoal can vacuum line. for the record, I pulled it off when I took the throttle body off. Just didnt put it back on... Starter is off so just waiting on hood to send me my hitachi. For the love of god, I hope that helps.

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

new starter installed.
VeloSyTy 1.0 EPROM installed.
vacuum canister hose reinstalled.

runs much better. not 100%, but better. gonna wait till i get paid and do new plugs, wires and gonna rebuild the accufab fuel pressure regulator. still want to do a bike tube/smoke test on monday.


as far as my original problem, i'm not 100% sure of how the truck should react on/off, part throttle, etc.. but vacuum seems better, still a little lean but didnt play around too much. i'm not going 18+:1 at a stop and almost stalling anymore. all in all, its better.

 

[5678TA]

Re: another idle problem..... low vacuum at idle in gear.

latest UPDATE!!!! went to the DEQ since i got a registration renewal. (turns out is was for the 454SS i previously had) Anyway, lady said i could do it now since i'm actually due in May. I FAILED. HC's were 380 and 430. She would not stay steady at 2500rpm. Wideband was going full lean, missing and popping.

Then went to the shop and tried the bike tube test. FINALLY, i know... nice loud HISSSSSS from what i believe was under the throttle body. ordered a throttle body gasket set. Will post results tomorrow. Also gonna do new cap, rotor, wires and plugs to mark that off the list since its a potential problem for high HC's and its time for a fresh setup.