Idle Help

[RebelYankee]

So I think I found the issue. The air duct is leaking where it clamps to the throttle body. New clamp, but still has a small leak. I cut a piece of innertube and put that under the clamp and that helped a lot. So a very small leak though. Short of replacing the air duct, any ideas?

 

[powershift]

Still chasing this issue. I did a smoke test and found some small leaks in the intake. The clamp on the throttle body was stripped. I replaced it (NAPA sells then as European Clamps) and that didn't fix the issue. Had the battery checked and is good. I checked the fuel rail pressures while driving, and the actual is always lower than the desired. Is that normal?

I haven't worked on that shudder problem before on an LR4, but if I found low fuel pressure that would be my top priority to fix. Look at the fuel filter and fuel pump.

 

[RebelYankee]

Thanks. That was my question about low pressure. At idle, the average actual fuel pressure is 3% lower than desired.

Is a 3% difference indicative of low fuel pressure or is it within acceptable range?

 

[jlglr4]

If you haven’t already done so, check your fuel trims using the gap tool. That should tell you if you have a vacuum leak, and might help diagnose low fuel pressure as well.

On these cars, you need to look at both short and long term fuel trim, and add the two together to get total fuel trim. Left and right banks are independent, so look at the banks separately. Check at idle, at 1500 rpms, 2500 rpms (in park or neutral, holding throttle steady as you can).

Vacuum leak will show as high positive fuel trims at idle that come closer to zero as rpms increase. Low fuel pressure will show as high positive fuel trims that tend to get worse at higher rpms.

 

[RebelYankee]

Thanks. I did this this morning after driving to work.

Bank 1 @ 619 RPM = 12.54%
Bank 2 @ 619 RPM = 9.37%

Bank 1 @ 1703 RPM = 5.47%
Bank 2 @ 1703 RPM = 3.12%

Bank 1 @ 2405 RPM = 8.64%
Bank 2 @ 2405 RPM = 7.81%

Looks like Bank 1 is higher, but not considerably. I did do a smoke test yesterday and saw no leaks. Wondering if this could be a MAF issue? Car has 95k miles and I don't know if they have ever been replaced.

 

[djkaosone]

How did you do your smoke test?

Through lots of trials and mostly errors, I found this process the most efficient. This process allows smoke to fill the engine first to easily find the leaks as fast as possible.

- Remove the harmonic intake tube
- Remove the oil cap
- Insert a "smoke machine inflatable bladder" for smoke testing into the throttle body, search on Amazon ,
- Start smoke machine, Amazon https://www.amazon.com/gp/product/B06XHRBKTM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1
- Once smoke comes out of the oil cap, close the oil cap

Now look for leaks.

 

[RebelYankee]

I removed the air filters and maf, plugged up one side of the resonator and inserted the bladder in the other side. This is how I found a leak where the resonator connects to the throttle body (fixed). I let the test run for a while and had good pressure and did not see any leaks.

 

[jlglr4]

Fuel trims are somewhat lean, but not terrible. Normal range is up to 10%. So maybe a little vacuum leak someplace, or dirty injectors, or combination. The PCV valve should probably be changed if not already done, but that tends to produce a bigger leak when it tears.

For the smoke test, you need to keep the butterfly valve in the throttle body propped open or you’ll only test up to the throttle body.

620 idle speed is not really too low. As i recall, mine is about the same once warmed up, but i don’t notice shudder or surging.

Reading through the posts again, your voltages look low. 12.2v seems pretty low at rest. I believe you want something around 12.6v engine off and everything shut down, and you should see something around 14v+ when running. The electronics stay on for a surprisingly long time, so testing when off I suggest popping the hood and leaving it open for a good 10 minutes before testing (and leave the key someplace far enough away that it doesn’t energize any systems when you approach).

 

[jlglr4]

Also - for testing voltages, don’t rely on the GAP tool. Test on the battery with a voltmeter. My gap tool always shows 12v or something like that, no matter what the battery is actually showing. I think it’s a glitch in the tool.

 

[RebelYankee]

Man, you are awesome. Thank you.
Great point on the butterfly, never thought of that! The battery is 4 years old, I do know that. I'll check voltages at the battery. I checked it myself and had autozone check for the hell of it, and it came back good both times. But I hear you need a good strong battery in these LR4's.