idle is loping

[Chip Hutchinson]

Hi All,
I just got my '96 LSI back from my daughter after 2 years (College). Today I started sorting out the problems. First thing to do was address the check engine light. Code reader indicated bank 2 knock sensor, so I purchased one and replaced it.
Well, now the light is off, but the idle cycles between 300 to 750 RPM about twice per second. Anybody have any helpful info on this?

Thanks

[svxfiles]

It sounds like a vacuum leak.
You could have broken a hose or knocked one loose.

[SoCal LS-L]

Mine has done this for a long time, only at a certain range in the warm-up cycle though and then its fine. I have traced all of my hoses and have found no leaks. If you want to do this methodically, download or just review the online service manual I link to below in my signature, and refer to the pdf titled "tests without codes".

At the bottom there is a flow chart for the idle issue..... and the pdf titled "system component tests" will give you the steps to test the sensors and solenoids.

[longassname]

99.99% chance you have an air leak. People often don't get the snorkle back on right. It's possible for it to look like it's on right but be buckled on the bottom.

[michael]

Behind the alternator there is a black box under the intake manifold. This box is for the IRIS valve it has a vacuum line that is very easy to break, I'd check that. You can also try squirting some carb cleaner on vacuum lines and listen for changes in idle to check for leaks. Please be careful not to spray it where it could ignite.

[Chip Hutchinson]

Thanks guys,
I was thinking vacuum leak too. I will check it out tonight, especially that iris valve. I had a lot of trouble getting my fat hands into that tight area to replace the sensor. I was leaning and rubbing pretty hard on anything in the way.

[MureZeriups]

My 250 HPDI runs very rough at idle and trolling speeds. I hate it. But it does start every time so its not all bad.

[svxfiles]

Originally Posted by Chip Hutchinson

Thanks guys,
I was thinking vacuum leak too. I will check it out tonight, especially that iris valve. I had a lot of trouble getting my fat hands into that tight area to replace the sensor. I was leaning and rubbing pretty hard on anything in the way.

May I ask how you changed which anti-knock sensor?
The front passenger side,
the rear drivers side',
I removed the intake manifold,
I removed the alternator,
went in through the tailpipe, ect.

[Chip Hutchinson]

Hi again,
I found the vacuum hose i knocked off. Put it back on and replaced the Bank 1 Knock sensor, in the hope that I won't have to be back in there any time soon.
It now runs and Idles well and has recovered the lost power from when it was running in "check engine" mode. Now I am considering replacing the PCV valve. The reason is that the oil dip stick always lifts about 3/8". Anybody have any helpful advice?
I was asked to describe the procedure I used for replacing the knock sensor. Here goes: Disconnect Negative battery connection. Remove the decorative covers from on top of the engine. Remove the cover above the Alternator/PSPump/ACCompressor. Remove the Alternator. At this point the Knock sensor bank 1 can be replaced. To replace the bank 2 (driver side) remove the tensioner assy from the AC compressor bracket and then the exposed portion of the AC compressor bracket. The Bank 1 is easier. Start the engine and check that the power steering works. Mine didn't and I had to tighten the Belt some more.
Hope this helps, and Thank You all for the good advice,

Chip.

[SoCal LS-L]

Replace the O-ring that seals the dipstick in the tube..... a new one will keep it from popping out.