Renix Low idle issues (not your average bear)

[Ecomike]

Since you like to experiment, like me, try disconnecting the O2 sensor, one at a time, then try the MAT (IAT), and then the CTS. I had an IAT that was off spec cause a high idle, so if the IAT is off in the other direction, I presume it could cause a low idle. A poor connection from the O2 sensor to the ECU could have a voltage loss biasing the ECU to raise or the lower air or fuel feed, and thus jacking with the idle speed.

I connected my O2 sensor back wards (electrical connector backwards once, by accident, the tab was busted) and it hunted up and down at 250 rpm.

 

[djgrayxj]

Note from DJ
You might go to NAPA and tell them you want two of each of these two parts.

Wire Terminal, GM Weather Pack Series OEM Terminal; 18 - 20 ga [small]
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NW_725150_0312357062
Type: GM Weather Pack Series
Product Line: NAPA Wire Series
Wire Size: 20-18 gage Tin plated brass
Part# 725150 – Male
Wire Terminal Mates W/ Part # 725151 below
OEM # 12033674 & 12089040
And
Wire Terminal, GM Weather Pack Series OEM Terminal; 18 - 20 ga [small]
http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=NW_725151_0312357060
Type: GM Weather Pack Series
Product Line: NAPA Wire Series
Wire Size: 20-18 gage Tin plated brass
Part# 725151 – Female
OEM # 12034051 & 12089188

These are the male and female connector’s terminals only, in most sensors that transmit info back and forth to the ECU. These make grate tools when inserted over or in there opposites and used as feeler gages to test for good tightness. Also when used with contact cleaner and rotated they make grate cleaning tools for their opposites. If you really want to get fancy and have something round and made of wood like an old lead pencil, you can cut off the tabs that you would normally crimp over the wires insulation, the drill the appropriate size hole in your wooden object then with a dab of hot glue you now have a nice handle or your new tool.

I keep wandering if you’re low idle is caused by a possible margin connection somewhere in your data path and not a component failure.

One more tip I use when back probing connectors. I found some neat straight pins at a fabric store (I think) that are about a 1 1/2" long with neat plastic heads on them that are about 1/8” across in in 8 different colors but the needle portion is very small in diameter with a nice sharp point. They slip right down past the wire insulation right into the connector. There are a large number of them in the plastic box and with the different colored heads for ID purposes you can insert them into the different connectors you want to back probe and leave them there until you are done. Just move your meter probes with small alligator clips attached from pin to until you are done testing things before removing all of the pins

 

[Ecomike]

I bought a small hoard of the GM weather pack fittings on Ebay last year, those metal pins and the plastic housings and elastomer seals are dirt cheap in bulk on ebay.

It could be poor contact resistance losses and or sensor drift from OEM specs, but I suspect Muad'Dib has already covered those possible issues, except maybe to verify exact temperatures and resistance at several temps on the IAT and CTS and the MAP (actual calibration tests using a calibrated thermometer and vacuum gauge-vacuum source). But Renix MAPs rarely go bad.

The one thing that still bugs me about Renix is not knowing the algorithm process control tree and what the priorities are when Renix has a conflict between air/fuel ratio (O2 sensor data) and the other sensor data (MAP, CTS and IAT-MAT data) and then tries to balance O2 stoich while fighting uncontrollable leaks at idle versus a desired idle speed. For instance if there is a small fuel leak at the fuel pressure regulator or an injector, or a vacuum leak letting in uncontrolled air, and renix is trying reach a programmed idle speed, but it has leaks beyond its control.

Oh, I just remembered!!!!! WE recently discovered that low idle can be caused by a clogged CCV line (the small one) or clogged valve in the valve cover, not letting the proper air flow (designed leak rate), through the entire CCV system! Also check the air filter for oil!!!!!

 

[cruiser54]

Your memory is great Mike, albeit short. Great idea to check the CCV lines.

The problem I'm having with O2 sensor is that it's not into play on a cold start, at least not for a minute or more.

 

[Muad'Dib]

I read that also, ive checked all my nice new CCV lines and orifice and they are all good to go. Tried a new 02 (i like buying parts and taking them back ) today just for shits and giggles with obviously no change in behavior.

IM wondering, would anything in the AC system cause this? Ive got a leaky heater core that im changing out this weekend.... and the only recent change around the time that this started being an issue was when i had my R12 evacuated. Again grasping at straws.

Of course my local u-pull-it doesnt have any Jeeps right now so i cant get my hands on a ECU .

Back to the heater core i go...

 

[cruiser54]

Somebody near you has gotta have an ECU. I've got one form my wife's 88.

 

[Muad'Dib]

Funny, (im mad as hell)...

Ive been having leakage on the Passenger floor. Thought it was Heater core. Started pulling carpet and items to replace heater core only to find out my whole WHOLE passenger side is filled with water. Turns out that the Audio installers that added and then removed a 2 gauge wire to my back amps (i upgraded to 00 gauge) didnt fill the hole into my passenger side... sooooooo as you can imagine there is alot of leakage into the passenger side of the jeep.

So now i must settle up with the Car Audio shop and put this on the back burner.. will reinvestigate in the future.

 

[Ecomike]

We found that making the the orifice hole a little larger will increase the idle!!! IIRC the OEM orifice was made larger in 88 or 89, versus the 87 year.

 

[cruiser54]

Woke up at 4 am and came up with a thought. You know the Torx headed air bleed adjuster on the driver side of the TB? Could it have some crud blocking the passage near it's tip? Try turning it out a ways (count the turns or partial turns) and see what happens to your idle. You can always turn it back in if it doesn't help resolve the issue.

 

[Ecomike]

Woke up at 4 am and came up with a thought. You know the Torx headed air bleed adjuster on the driver side of the TB? Could it have some crud blocking the passage near it's tip? Try turning it out a ways (count the turns or partial turns) and see what happens to your idle. You can always turn it back in if it doesn't help resolve the issue.

He is not using a Renix Throttle body. He posted earlier "Im using a 68mm from a Dodge Dakota", but trash or a thin build up in the CCV tube, or TB bypass ports sounds like a possible issue. What about the Evap system, is a small continuous leak like the CCV? I would look for a prior small leak that sealed itself off, in part of completely.

 

[cruiser54]

Good point. The later TBs have no air bleed then?

I'd try just unplugging the CCV hose at idle and see what happens then.

 

[Ecomike]

Good point. The later TBs have no air bleed then?

I'd try just unplugging the CCV hose at idle and see what happens then.

I have no idea what they look like or have. Just pointing out it was not OEM.

But I know enough about physics that I know a slight change in the orifice diameter or CCV tube wall apparent inside diameter on the CCV tube can have a large effect (R squared) on the controlled leak that feeds most of the idle air flow. I would think the IAC would be able under new factory OEM conditions to move the idle below 750 rpm to force a richer condition if needed, but I do not know that to be true. If it is true, then I would suspect something odd in the sensors, wiring and controls. But Renix does so much odd idle stuff, I just have never been sure what was normal.

 

[Muad'Dib]

FWIW, when i was doing testing i did disconnect one of the CCV tubes and i got an instant high idle. I am using 96 era CCV tubing and orifice and it hasnt been an issue in the past. It is clean.

Again, the issue seems to be narrowed down to the IAC completely closing.. why its doing this is the unknown. From studying the FSM it looks like it adjusts based on the inputs the ECU sees in the different modes of operation.

Again, i will reiterate that this is on hold until i can get the car audio company to make right with me.. for all i know this flooding issue has been causing the idle issue. The water was/is high enough to make contant with tons of wiring.. so who knows if i was having some weird short to ground.

 

[2stix]

should the ohms resistance on the TPS ground change when the key is on? with key off i get 0.5 ohm. but with key on engine off i get 25.5 ohm. with key on engine running i get around 30-31 ohm. could this be part of my low idle/ running rich problem? i can sometimes get it to run excellent and with perfect idle by fiddling with the tps connector and give it a little rev. but it will go back to running poorly once i shut it down and restart.

 

[cruiser54]

Resistance should be tested key off. Perhaps this will help you with your resistance test.

Cruiser’s Renix Sensor Ground Test
Set your meter to measure Ohms. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.

 

[2stix]

yes i understand that procedure, and that is how i got my original 0.5 ohms. so i figured my ground properties where good. while setting the tps (again) i noticed that the idle will change when i mess around with the connector. so i tested ohms again with engine running and got 25.5 ohms. should i be getting increased resistance with the engine running? if no, then can i splice in an additional ground wire to the tps harness to ensure a better ground while key on?

 

[Ecomike]

When the engine is running there is back voltage on the TPS ground that gives a deceptive ohm reading on ohm meters. You can only get a true ohm reading with the power OFF.

Try checking the ohms, power off, while wiggling the TPS connector, then do the same on volts, with power ON, and see if there is a voltage drop across the TPS connector Need to pierce the insulation and take readings on the same wire on each side of the connector using the battery ground for the negative meter lead, or just replace the TPS connector, or clean and tighten the female ends of the connector.

The 25 to 30 ohms you see with power on is typical as recall ( I often forget to switch my leads on my digital meter, so I have seen by mistake), but may vary from meter to meter.

 

[2stix]

ok thanks mike, that makes sense. i just wanted to be sure. i have done all the other things mentioned. i have come to the conclusion that the connector is actually good. i just came from trying yet another TPS (spare) and at first was getting that huge idle (lets say 3000 rpm) so i quickly disconnected the TPS which brings the idle right down, but low. i them re connected the TPS and the idle came up to normal. yippie. i take it for a test drive and it runs excellent again. power is back, idle is perfect. come back and turn the engine off. i restart and get the low idle again. same thing when i had the first TPS in. only thing i can figure is that i am somehow giving the computer a jump start sort of speak by unplugging then replugging the TPS while running. this seems to do something to the TPS or computer to make it run perfect. but as soon as i shut it off and restart, it goes right back to low idle and poor power. not extremely poor power, but definitely a difference.
any ideas?

 

[Ecomike]

First I suggest you start a new thread on just your problems, and history and let us start with a fresh thread and fresh perspective, and then we can leave this hijacked thread back to the OP, LOL!

 

[2stix]

no offense mike, but i was under the assumption that it was better to NOT start another thread on the same subject. i have the exact same issues with my renix as the OP. and have pretty much tried all the things this thread has suggested. i am just trying things that have not yet been mentioned and adding to it. but if starting a new thread is proper, than i have no problem starting another.