Low RPMs at idle & reading around 1800 rpm at 60 mph.

[tintlife]

07 hoe so I know it was needing a few things. When the low rpm started I have only gotten code for 02 sensor. Bank 1 sensor 2. I have replaced plugs and wires 230k bought when it had 130k 2 years aago.went ahead and installed new style valve covers and was taking 2 cranks to start so replaced fuel pump also. Waiting for 02 sensor to arrive but would a 02 sensor cause rpm so low it snds like it shut off. Hasn't done that yet. The high rpm on highway is new it just started about week ago. Only thing I have changed is I finally installed my front lowering struts but only dropped 1 1/2" in front. My abs and traction control has bn on since I lowered rear 2 years ago. Installed new wheel sensors and still there but no code. Any ideas? Sorry for the long ass explanation. I'm not one to ask for help but I'm stumped at this point. Also new throttle body and maf.

 

[Doubeleive]

07 hoe so I know it was needing a few things. When the low rpm started I have only gotten code for 02 sensor. Bank 1 sensor 2. I have replaced plugs and wires 230k bought when it had 130k 2 years aago.went ahead and installed new style valve covers and was taking 2 cranks to start so replaced fuel pump also. Waiting for 02 sensor to arrive but would a 02 sensor cause rpm so low it snds like it shut off. Hasn't done that yet. The high rpm on highway is new it just started about week ago. Only thing I have changed is I finally installed my front lowering struts but only dropped 1 1/2" in front. My abs and traction control has bn on since I lowered rear 2 years ago. Installed new wheel sensors and still there but no code. Any ideas? Sorry for the long ass explanation. I'm not one to ask for help but I'm stumped at this point. Also new throttle body and maf.

how long ago was the throttle body replaced?

 

[tintlife]

how long ago was the throttle body replaced?

Less than 2 weeks ago. I have had low rpm issue since end of April. But high rpm recently and sluggish when accelerating. I maybe wrong but starting to think it may end cats. Could be wrong but I'm damn near out of other options. Lol

 

[dwinters14]

Less than 2 weeks ago. I have had low rpm issue since end of April. But high rpm recently and sluggish when accelerating. I maybe wrong but starting to think it may end cats. Could be wrong but I'm damn near out of other options. Lol

02's don't control idle, they simply read the air data and report it to your computer which then makes adjustments. If you have a scan tool you can monitor the 02's to see if they're working properly. 0.0v to 1.0v is the typical operating range for a working upstream 02 sensor. Can you record live data? Check your gm/s from your MAF as well as your long and short term fuel trims. You may have a vacuum leak as well somewhere, or a sensor like a TPS isn't working properly.

Live data can rule out 90% of these issues without throwing parts at it, a lot of this info is still fresh in my mind from tracking down some issues on my truck I can at least steer you in the right direction.

 

[Doubeleive]

ya the maf & throttle body are going to be what you need to take a look at.
did you use oem or aftermarket?
if you suspect cat's you can do a backpressure test
might want to also monitor the fuel pressure

 

[tintlife]

Yea I will do the live data test. I didn't think 02 would have anything to do with it but wasn't sure. Maf is oem throttle is aftermarket. When the high rpm started at higher speeds it now backfires when I let off which is also something new. There is times it struggles to get to highway speeds. But will check data test when I get some free time tomorrow afternoon. I do appreciate the help! I have scrolled thru this forum for year or so and finally actually needed some assistance. Lol

 

[j91z28d1]

you honestly need a good scanner they can read all the non standard codes so you can fix all chassis issues. when you lowed the back, did you do shocks? there's a plug on top of the passenger side frame rail everyone knocks off when they change shocks. I did it myself. threw stability lights.

have you rebuild or done any work to the tranny? I'm going to throw it out as a guess but if you haven't, low idle but not running badly, rear after the cat o2 isn't really a big deal. slipping or atleast a torque converter that isn't locking up like it used to on the interstate, feeling sluggish. sounds like converter that isn't locking up like you're use to

I've be checking for burnt tranny fluid, could send off a sample for test and check the magnet in the pan for shiny stuff.

 

[dwinters14]

you honestly need a good scanner they can read all the non standard codes so you can fix all chassis issues. when you lowed the back, did you do shocks? there's a plug on top of the passenger side frame rail everyone knocks off when they change shocks. I did it myself. threw stability lights.

have you rebuild or done any work to the tranny? I'm going to throw it out as a guess but if you haven't, low idle but not running badly, rear after the cat o2 isn't really a big deal. slipping or atleast a torque converter that isn't locking up like it used to on the interstate, feeling sluggish. sounds like converter that isn't locking up like you're use to

I've be checking for burnt tranny fluid, could send off a sample for test and check the magnet in the pan for shiny stuff.

This. Could be a trans related issue as well. Honestly could be two separate issues that are unrelated. IMO here's where to start for the low idle.

Firstly identify if only your idle is low. How does the vehicle accelerate? Under 25% throttle? Under 50% throttle? To redline? How does it drive with load? I.E. Up a hill in overdrive? In tow mode? Hot vs cold? This is the best way to try and pinpoint exactly what is going on. Try to isolate the problem. So many things can affect the idle of the vehicle because it requires spark, air and fuel.

Here's a few general steps you can do to check that most things are working correctly.

With the key on and the live data engaged, confirm the throttle position is being read and without any gaps or skips. You can do this by depressing the pedal slowly while watching the value go up. Make sure there's no skips, and if you can, have someone actually watch the throttle to verify it is doing what the pedal is reading. I believe at idle my throttle position percentage is about 18%, sometimes it'll dip down to 17% and my idle is about 450RPM ~ 600RPM depending on the situation, but averages out about 500/550RPM.

Verify fuel pressure at key on and while running. Should be in and around 50PSI, this will rule out any fuel pump/clogs in the line issues. Then once running confirm fuel trims. Should be ~ 6% for both short and long term fuel trims closer to zero but can go up to 10%. My truck never went negative, but apparently they can and still be within spec. If you have a mechanics stethoscope touch the injectors and listen for them firing, they make a loud clacking noise. MAF's should read about the L of the engine. If you have the 5.3L the GM/S should be in and around ~ 6 GM/S.

Beyond that do a visual inspection for leaks both in fuel and air,. Smell for any leaking gasoline, listen for any whistles for potential vacuum leaks as well. Report back what you find and hopefully we can help narrow down the cause.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.