Vacuum leak detector...works well
 

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So, been chasing a cold start idle and overall idle quality problem for a while now. I tried replacing and calibrating the IAC valve, adding a 1" spacer, mucking with physical blade adjustments and software parameter adjustment (AFR, idle target) to no avail.

Continuing this effort, I employed a pressurized smoke machine to look for vacuum leaks and disassembled my throttle body for inspection and cleaning. The cleaning didn't seem to do anything that I could make out as the unit is not too crusty but went through the steps anyway.

With the smoke tool, I found massive leaks on both sides at the rear of the mounting flange. Also noted smoke seeping from the very front of the flange. After some research, determined that my intake...Edelbrock 2161, is known to leak when using a square bore carb (my tbi is square bore). Edelbrock came out with a carb adapter plate (20 bucks) that makes this go away. I picked up the plate, installed it and now have no leaks.

The first cold start after this was 50% less bad and subsequent warm starts also seemed to be better. Overall idle quality is much improved. My suspicion is that with the vacuum leaks, the system was dumping more fuel and learned to continue doing so (fuel maps were richened up driving with the leaks). Now that the leaks are gone, I'm running rich. This should self adjust going forward and so I expect things to continue to improve.

Need to complete about 4 more cold starts and do some stop and go driving with more warm starts in order for it to adjust.

-Kevin

Re: Vacuum leak detector...works well
 

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The throttle body. The thing has all this incorporated:

TPS
ECT
IAT
MAP
IAC
Fuel Pressure sensor
ECU

Fuel rail
4 80lb injectors

-Kevin

Re: Vacuum leak detector...works well
 

Good find. Back to basics before anything else.

Re: Vacuum leak detector...works well
 

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Today's cold start didn't go perfect but it is a major improvement. Time and more learning will tell though...

https://youtu.be/z6jH39CdAfA?si=nV4qFVyoZa0NX5N_

-Kevin

Re: Vacuum leak detector...works well
 

And I thought a DualJet was difficult to tune ?

Re: Vacuum leak detector...works well
 

Some more information on the smoke machine would be appreciated. It may be what I need to solve the less than perfect idle on my S10 Blazer.
Thanks

Re: Vacuum leak detector...works well
 

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This particular smoke machine was an Amazon purchase years ago for 25 bucks or so. Can't find it out there now for that price. The closest is a kit to build on ebay and something similar on Amazon (links below).

Its a very basic design using a household paint can (1 gallon), air regulator, wick, coils, battery connecting gator clips with wires, fittings and tubes. The idea is suspend the wick into mineral oil in bottom of can, wrap wick in a wire or coil and give that + and - from 12v vehicle battery, thus creating the smoke. Plumb the inbound, regulated air into the pressure chamber and have an outlet near top for your 7-10 psi smoke. I think the parts to build this would be <20 bucks, maybe WAY less.

--Very close to what I used...
https://www.ebay.com/itm/22476533833...Bk9SR_jehLzVZA

--Very expensive clone on Amazon
https://www.amazon.com/AutoLine-Pro-...296559982&th=1

Hth,

-Kevin

Re: Vacuum leak detector...works well
 

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Yesterday I spent a few hours fine tuning idle with blade adjustment, richening up the idle AFR in an effort to bring the IAC "counts" down to below 10 in gear. This is the amount of work the IAC is doing to keep target idle rpm. The goal was to give it almost no authority to reduce idle rpm while keeping it in range of having immediate authority to increase idle rpm.

When done, I had the warm/hot start sequence functioning perfectly....it starts, idles up and then settles into a nice idle near the target of 700 with 0 IAC count. I pull it into gear and the idle drops slightly with IAC counts around 10. Pull it out of gear, the idle goes up a couple hundred rpm and then settles a bit back near target.

Went to cold start today and it was perfect. Let it warm to FOT where it warm/hot starts just as it did yesterday.

Success!

-Kevin

Re: Vacuum leak detector...works well
 

Another way is to spray carb cleaner on the carb/FI at the base.

Re: Vacuum leak detector...works well
 

Thanks for all the information! I'd spend the price of that kit in carb cleaner trying to track down all the vacuum hoses on the truck.
Much appreciated.