Jump to content

Normal Idle Speed at Operating Temp?


Recommended Posts

I tried looking this up but found more info on this relating to the AW4, where idle rpm can vary depending on if it's in drive/park/neutral.

 

So what is the normal factory idle, at operating temperature/closed loop, stopped, manual transmission, neutral, no accessories/loads, Renix 4.0L?

Link to comment
Share on other sites

Does the tachometer's 0-1000 increments go from 0-500, 500-750, 750-1000? It's weird because it's missing the 0-250 like the other 1000s...

I'm assuming its scaled properly from 500-1000, but then the 0-500 is compressed for some reason.

Link to comment
Share on other sites

  • 2 weeks later...

Here's where my idle is at now:

 

3AKKwKF.jpg

(I'm assuming this is 500rpm, hard to tell with this scale skipping)

 

 

A little background:

In an attempt to correct my hunting idle, I did the following:

- completely removed and thoroughly cleaned throttle body

- adjusted butterfly stop screw

- removed, cleaned, & re-installed IAC (Q: Is there meant to be a gasket - in addition to the o-ring??)

- cleaned mating surfaces and installed new throttle body gasket

- adjusted TPS according to Cruiser's tip for engine TPS adjustment (0.83 Volts)

 

Interesting part is when I first start it up, it goes to (what I think is normal) 750 rpm idle, and stays there for a while. Then after driving it a bit, it goes down to the ~500 mark.

The idle is still hunting around, acting the same as before these adjustments, but just at a lower rpm.

Link to comment
Share on other sites

  • 2 weeks later...

Still having trouble with my idle here... I thought it could have been the IAC valve since I tried cleaning that really well and thought I may have damaged it with all the throttle body cleaner I used. So I purchased a new one and installed it today. 

No luck, may be even worse now. I have the same problem: idles around 750 rpm, but once it gets up to operating temp, then it drops down to 500 rpm. However, this time I noticed that when I revved it up it almost stalled when it dropped back down, so I shut it off and left it at that.

What could that be? Why would a brand new iac make that condition worse?

 

For what it's worth, I bought the Standard Motor Products AC12, I read that was a good quality one.

Link to comment
Share on other sites

I read through another thread on here that had a similar problem, and thought it might be the O2 sensor. I replaced the O2 sensor today since the one in there was one from 1990 and I wanted the peace of mind. Anyway, that didn't do anything, still the same.

 

I thought I read that renix 4.0s don't have a warm-up idle, is that true? It seems once the t stat opens up the idle drops to 500, weird...

Link to comment
Share on other sites

I would check the TPS. I have a stalling problem as well. TPS and MAP sensor. And when replacing the TPS (if it comes to that) try and find a MOPAR replacement. They're not bad priced on Ebay if you search hard enough. Have someone get you a part number if you can. The reason I say get a MOPAR one is because I had an Airtex and it lasted a total of 10 minutes. I currently have a Standard Motor Products one and I kinda have a gut feeling it is what my problem is. Just really don't want to buy ANOTHER TPS. Already changed my fuel regulator and O2 sensor twice...

Link to comment
Share on other sites

I wonder if it's giving power to the internal heater of the O2 sesnor. Bad relay? One closest to the radiator in that bank of relays on the passenger fender, right behinf the big starter relay with all the wires on it. 

Link to comment
Share on other sites

Checked the relay, it's good. (clicked 85-86, and 0 ohms 34 to 87)

 

Checked the wiring to the O2 sensor:

- could not get 12-14V from the heater (orange wire)

- got 5V solid for O2 signal to ECU

- 0.01 ohms ground to neg battery

(A = orange (heater); B = black (common ground); C = grey (O2 - ECU) <---- This is correct, right?

 

 

For the heater test, do I need to have the engine running and back-probe? Or can I just have ignition on?

Link to comment
Share on other sites

For the HOs, the engine has to be running to measure the O2 sensor 12V heater voltage since the voltage comes from the ASD (Auto Shutdown) relay. I would ASSume the Renix is the same as you don't want the O2 sensor heater coil energized w/o the engine running. But it's Renix, so who's knows - they are not logical. Try disconnecting the O2 connector, start the engine, and check for 12V across the heater supply and return pins, harness side. Also measure the resistance across the same pins while disconnected, engine off, on the sensor side. The O2 heater coil resistance should read ~5 ohms.

Link to comment
Share on other sites

Checked the relay, it's good. (clicked 85-86, and 0 ohms 34 to 87)

 

Checked the wiring to the O2 sensor:

- could not get 12-14V from the heater (orange wire)

- got 5V solid for O2 signal to ECU

- 0.01 ohms ground to neg battery

(A = orange (heater); B = black (common ground); C = grey (O2 - ECU) <---- This is correct, right?

 

 

For the heater test, do I need to have the engine running and back-probe? Or can I just have ignition on?

Have it running to be sure. 

Link to comment
Share on other sites

My truck still has some idle issues before it's warmed up, which is kind of the exact opposite of yours.  Once my engine reaches temp, it holds a strong and solid 600rpm idle.  Anything below that, or if I shut it down and it sits for a few minutes, it takes a minute or two to get back to a steady idle.  When the idle waivers, it sometimes sounds like it is about to stall out, then it bumps right back up to a good idle.  Rather confusing at this point.

Link to comment
Share on other sites

My truck still has some idle issues before it's warmed up, which is kind of the exact opposite of yours.  Once my engine reaches temp, it holds a strong and solid 600rpm idle.  Anything below that, or if I shut it down and it sits for a few minutes, it takes a minute or two to get back to a steady idle.  When the idle waivers, it sometimes sounds like it is about to stall out, then it bumps right back up to a good idle.  Rather confusing at this point.

Tested O2 sensor?

Original injectors? 

Link to comment
Share on other sites

O2 sensor heater is working, and although I don't have an analog meter, I did see 1-4 volts alternating, so I think O2 sensor + wiring is good.

 

i read it could be related to intake/exhaust gasket, and I did notice this checking it out:

zcjmXsb.jpg

 

Seems like just one bolt is missing, not sure if that's a big deal, but I will get a replacement from the junkyard soon.

 

I also have the 746 injectors and am thinking I will combine jobs by taking fuel rail off, replacing intake/exhaust gasket, re-torqueing with all bolts present, then putting in the new injectors.

Link to comment
Share on other sites

Hey everybody, thanks for trouble shooting me through this, what do you make of this recent discovery:

 

- I have the engine at operating temp, idling low at 500 rpm

- I loosen TPS, adjust it up till idle goes to 750 rpm, tighten T20's back down

- idle stays there, I think everything is back to normal, yay!

- I drive it around for a bit, rpms go back to 750 like it should at idle

- I get back home after a 5-10 minute drive, the idle is back to 500 rpm again.....

 

Maybe I don't fully understand the tps, and that is normal behavior.

Anyway, I re-adjusted the tps using 17% of 4.88 = 0.829 V, and I'm back to square one here.

Also, I went through the throttle's full motion and watched the tps voltage, smooth throughout the range.

Is it safe to rule out the tps, or did this adjustment test prove anything?

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...