The RENIX low Idle chronicles, long read!

[Ecomike]

Most people do not appreciate the complexity of the OEM CCV routing. I suspect the mod you made on the front side of the valve cover to the throttle body air intake is not equal in terms of vacuum at various points, like idle, WOT, acceleration and deceleration. The stock system ran back to the clean side of the air filter (IIRC???), inside a very large opening (the air filter box), not back into a 3" dia tube right at the throttle body opening.

The rear manifold orifice (stock) is designed to control the flow rate of air sucked out of the crankcase via the valve cover connection. When there is little blow by gas, the make up air is supplied front the front CCV line, which in the stock OEM set up is also under some vacuum, but not much vacuum, not nearly as much vacuum as the rear connection, as it is on the clean side of the air filter box.

I suspect the OEM CCV set up was a carefully thought out balancing act of variable vacuum rates, and gas flow scrubbing action in the crankcase on both sides of the throttle body at various times!!!!

 

[xjtrailrider]

Mike, you nailed it! I drilled the orifice out in steps until I got the idle around 750 in neutral and 600 in gear.

What a difference! Now my XJ will idle with the lights/wipers/AC and stereo all running at the same time.

Its amazing what a controlled vacuum leak can do!

I wonder if this will help mileage or hurt it?

 

[cruiser54]

Won't hurt your mileage. Interesting fix.

I guess we need to remember that on our fuel injected engines using a throttle body that has a closed butterfly at idle, that our idle speed is regulated by nothing other than sophisticated vacuum leaks. One is the CCV system and the other the Torx air bleed screw on the passenger side of the TB under the metal cap.

 

[xjtrailrider]

So far, no noticeable changes in mileage but I have not run the numbers yet. The Jeep definitely runs better/smoother at idle even with the alternator being taxed and the AC compressor running.

 

[Ecomike]

Mike, you nailed it! I drilled the orifice out in steps until I got the idle around 750 in neutral and 600 in gear.

What a difference! Now my XJ will idle with the lights/wipers/AC and stereo all running at the same time.

Its amazing what a controlled vacuum leak can do!

I wonder if this will help mileage or hurt it?

If it helps solve a hunting idle, that hunts up and down, it should improve the MPGs by getting a stable idle, if it just raises a low idle it will use more fuel, but in the long run, a low idle may cause other issues that hurt long term MPGs, as a low idle might build up carbon fouling faster 9and hurt mpgs later with pinging, preignition), or trigger a hunting cycle, or cause voltage issues if the alternator runs to slow, leading to other issues....

In other words, a complex variable question, so no easy answer.

Of course that assumes you spend lots of time running it at idle?, like on an interstate freeway parking lot at 5 pm, LOL!!!!:cheers:

 

[xjtrailrider]

Of course that assumes you spend lots of time running it at idle?, like on an interstate freeway parking lot at 5 pm, LOL!!!!:cheers:

Well fortunately for me, the city I live in has very few traffic issues. If there is more than 5 cars at a stop light, we call that a traffic jamb. My daily commute is 10 miles total at 45mph.

Gotta love a small town!

The Jeep is running better than it ever has, my wife road in it last night when we went to dinner and even she noticed how much better it is.

 

[bigalpha]

Mike, you nailed it! I drilled the orifice out in steps until I got the idle around 750 in neutral and 600 in gear.

What a difference! Now my XJ will idle with the lights/wipers/AC and stereo all running at the same time.

Its amazing what a controlled vacuum leak can do!

I wonder if this will help mileage or hurt it?

Crazy. Do you have a pic of your vacuum harness set up? I have a chronically low idle (esp. at start up) and wonder if my vacuum set up is wonky.

 

[xjtrailrider]

Crazy. Do you have a pic of your vacuum harness set up? I have a chronically low idle (esp. at start up) and wonder if my vacuum set up is wonky.

Not really but its all done to the vac diagram on the firewall just not with the plastic hose. I'm using 2 cycle fuel line(commercial grade, not the cheap stuff)

The only thing that was not done as stock was the CCv and that turned out to be the issue. The stock RENIX plastic hose mess has plenty of leaks even on a good day and new. I threw that stuff out years ago.

 

[blondejoncherokee]

"I drilled the orifice out in steps until I got the idle around 750 in neutral and 600 in gear."

So do you mean the rear crank case cover orifiuce for the CCV or the front one? or both?

so do you have pics of what you did? I have had a 250 idle for years, but the jeep runs good so I've never thought much about it.

 

[2stix]

the one in mention is the small one in the rear of the engine. normally has a white plastic piece. you drill out that white piece to gain a little more volume.
i did not actually drill mine but changed tip sizes. each time i tried, the idle would raise a bit, but then the ECU would compensate and lower it back down.
you mention your jeep has idled at 250 for years, does it run rich? pass emissions test? being in Sac. i would think your emissions program has just as strict rules as we do in san diego.

 

[cruiser54]

"I drilled the orifice out in steps until I got the idle around 750 in neutral and 600 in gear."

So do you mean the rear crank case cover orifiuce for the CCV or the front one? or both?

so do you have pics of what you did? I have had a 250 idle for years, but the jeep runs good so I've never thought much about it.

The wihite plastic orifice that fits into the rear valve cover grommet.

 

[blondejoncherokee]

ok good to know. ill try giving it a shot.

"does it run rich? pass emissions test? being in Sac"

ya its scary out here. When I first got the rig it used to barely pass smog by a hair. Now its fine. I am meticulous about sensor replacement, ground refreshing, and major tune ups and cleanings twice a year.

yes it used to, but it would still pass, but the techs would always say it was running rich. Now it passes even better but I have a brand new cat and do a massive tune up twice a year. On top of that, i put in like 2-3 pints of acetone a week before smog, then one more pint or two on the day of, adn the last few times it has smogged with very low emissions. so low the tech was pretty surprised.