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RENIX idle adjustment screw?

xjtrailrider

NAXJA Forum User
NAXJA Member
Location
Roanoke VA
I know what/where it is but what is the proper setting for it. Mine had been monkeyed with a long time ago and since I have a low idle issue I think there may be a issue with were it is set. Some one had bent the tab on the throttle were it contacts the screw as well.

If some of the RENIX gurus could give me the setting spec and how to achieve it I may be able to finally cure that idle ill on my 90'.
 
I think the throttle stop is there just to keep the throttle plate from slapping the inside of the TB. There is a bypass air adjustment under a cap on the drivers side of the TB. But my experience is the ECU is going to try to adjust the idle back down again, as soon as the ECU goes into open loop.
If you adjust the throttle stop, you have to readjust the TPS, which can also change your idle a little,
The whole process reminds of a dog chasing his tail, my be great fun but largely unrewarding.
Renix tends to idle a little low IMO, 450-500 isn't unusual.
I'd adjust the stop so the throttle plate is a paper thickness off of the TB wall and then adjust the air bypass (after cleaning it out) so it idles around 500 in closed loop. You may still get some idle fluctuations as the motor changes from open to closed loop, but then you can do some fine adjustments and likely split the difference between you high idle and low idle fluctuations.
 
8Mud said:
I think the throttle stop is there just to keep the throttle plate from slapping the inside of the TB. There is a bypass air adjustment under a cap on the drivers side of the TB. But my experience is the ECU is going to try to adjust the idle back down again, as soon as the ECU goes into open loop.
If you adjust the throttle stop, you have to readjust the TPS, which can also change your idle a little,
The whole process reminds of a dog chasing his tail, my be great fun but largely unrewarding.
Renix tends to idle a little low IMO, 450-500 isn't unusual.
I'd adjust the stop so the throttle plate is a paper thickness off of the TB wall and then adjust the air bypass (after cleaning it out) so it idles around 500 in closed loop. You may still get some idle fluctuations as the motor changes from open to closed loop, but then you can do some fine adjustments and likely split the difference between you high idle and low idle fluctuations.
Thanks, I only get a "open loop" idle for a few seconds and then it will step down to about 350-400 rpm. I've verified the idle with another tach. In the summer it never steps the idle up at all on cold start. I'm getting ready to try another TPS just for kicks. I have another issue with it as well, when I let off the throttle while cruising the rpm kicks up like it is down shifting for a second or 2. It will do the same when I get back on the gas it will kick back and then go into OD. That may be normal, not sure but I got a freebie new OEM TPS so I thought I would play a little.

I forgot to add that otherwise it is running perfect so I may just be chasing a ghost.
 
xjtrailrider said:
Thanks, I only get a "open loop" idle for a few seconds and then it will step down to about 350-400 rpm. I've verified the idle with another tach. In the summer it never steps the idle up at all on cold start. I'm getting ready to try another TPS just for kicks. I have another issue with it as well, when I let off the throttle while cruising the rpm kicks up like it is down shifting for a second or 2. It will do the same when I get back on the gas it will kick back and then go into OD. That may be normal, not sure but I got a freebie new OEM TPS so I thought I would play a little.

I forgot to add that otherwise it is running perfect so I may just be chasing a ghost.

The last part you mention here sounds more like a sticky EGR valve. This is what my jeeps is doing at the moment. Clean it or replace it, and i would bet the "downshifting" you describe will go away. So will the lower idle.
 
xjtrailrider said:
Thanks, I only get a "open loop" idle for a few seconds and then it will step down to about 350-400 rpm. I've verified the idle with another tach. In the summer it never steps the idle up at all on cold start. I'm getting ready to try another TPS just for kicks. I have another issue with it as well, when I let off the throttle while cruising the rpm kicks up like it is down shifting for a second or 2. It will do the same when I get back on the gas it will kick back and then go into OD. That may be normal, not sure but I got a freebie new OEM TPS so I thought I would play a little.

I forgot to add that otherwise it is running perfect so I may just be chasing a ghost.
That could also be a TPS adjustment issue. I would get the multimeter and re-check the TPS settings just to rule out that gremlin.
 
Muad'Dib said:
The last part you mention here sounds more like a sticky EGR valve. This is what my jeeps is doing at the moment. Clean it or replace it, and i would bet the "downshifting" you describe will go away. So will the lower idle.

EGR has a blockoff plate between it and the intake and a gasket on each side of the plate. The vacuum line is plugged as well
 
Have you made any progress with this? Im still suffering with a low idle (its at the first line on the tack when in gear). Ive tried 3 different TPS's, and i replaced the IAC and fixed my sticky egr. I swapped out my TB with a different one (because my old one was stripped where the TPS bolts on so i could never adjust it correctly). I tightened the "air bypass" (as it was described above) and i adjusted the "stop" to where the throttle plate stays open enough to where you can put a paper through it.
It does seem to idle in the correct range when in park. Once it is in gear however the idle drops down to the first line on the tach. Is this because of that "air bypass" screw not being adjusted correctly? Or something else? All my grounds are clean. Last month i replaced my exhaust manifold, and the bolts are all still tight. No vacuum leaks etc. Fixed everything else this is really the only problem that is left. Even idling this low, it doesnt stumble, hesitate or anything. I would almost leave it like this except that when it idles this low, the alternator doesnt get turned fast enough to put out enough current to only run the heater and the lights. (The Voltage drops to about 10 it seems).

Any suggestions for me? Sorry to hijack!
 
I had the exact same issue, along with a 2 other guys I know. The throttle body should not be adjusted. TPS sure but don't touch the throttle body. I have replace 2 throttle bodys with the exact same is and no problem since.
 
Muad'Dib said:
Have you made any progress with this? Im still suffering with a low idle (its at the first line on the tack when in gear). Ive tried 3 different TPS's, and i replaced the IAC and fixed my sticky egr. I swapped out my TB with a different one (because my old one was stripped where the TPS bolts on so i could never adjust it correctly). I tightened the "air bypass" (as it was described above) and i adjusted the "stop" to where the throttle plate stays open enough to where you can put a paper through it.
It does seem to idle in the correct range when in park. Once it is in gear however the idle drops down to the first line on the tach. Is this because of that "air bypass" screw not being adjusted correctly? Or something else? All my grounds are clean. Last month i replaced my exhaust manifold, and the bolts are all still tight. No vacuum leaks etc. Fixed everything else this is really the only problem that is left. Even idling this low, it doesnt stumble, hesitate or anything. I would almost leave it like this except that when it idles this low, the alternator doesnt get turned fast enough to put out enough current to only run the heater and the lights. (The Voltage drops to about 10 it seems).

Any suggestions for me? Sorry to hijack!
don't trust the factory volt gauge, it's worthless. Mine shows an instant 2 volt drop when I turn on the heater because the wiring into the cab is smaller than it should be.
Check it with a DMM at the battery terminals and I bet you'll find all is well, and messing with the idle really isn't what you want to do.
 
87manche said:
don't trust the factory volt gauge, it's worthless. Mine shows an instant 2 volt drop when I turn on the heater because the wiring into the cab is smaller than it should be.
Check it with a DMM at the battery terminals and I bet you'll find all is well, and messing with the idle really isn't what you want to do.

I have checked it in other areas, mainly for current not voltage. The drop is significant.
I dont want to mess with the idle? Even when it is down at the first line on the tach?
 
Muad'Dib said:
I have checked it in other areas, mainly for current not voltage. The drop is significant.
I dont want to mess with the idle? Even when it is down at the first line on the tach?
A few questions, how does it idle when it's cold, warm and hot? Does the idle change?
Closed loop warm motor idle has more sensor inputs than just about any other function on the motor. There is a lot to go wrong.
Changing the idle air on the TB causes a whole chain reaction.
I can give you a few things to try, but finding the root cause will likely be luck more than skill.
 
8Mud said:
A few questions, how does it idle when it's cold, warm and hot? Does the idle change?
Closed loop warm motor idle has more sensor inputs than just about any other function on the motor. There is a lot to go wrong.
Changing the idle air on the TB causes a whole chain reaction.
I can give you a few things to try, but finding the root cause will likely be luck more than skill.

When the engine is cold, or only been running for a few minutes the idle when in gear is actually slightly better when its fully warmed up. (Still not quite where it should be) It seems to be about at the first line if its warm or hot.
Could this be caused by a faulty 02 sensor. Ive changed it already about a year ago, but ive always been conceared about it for one reason or the other. I think because when i purchased it, the counter jock pit his fingers on the end of it...
 
Muad'Dib said:
When the engine is cold, or only been running for a few minutes the idle when in gear is actually slightly better when its fully warmed up. (Still not quite where it should be) It seems to be about at the first line if its warm or hot.
Could this be caused by a faulty 02 sensor. Ive changed it already about a year ago, but ive always been conceared about it for one reason or the other. I think because when i purchased it, the counter jock pit his fingers on the end of it...

I imagine any oil from his fingers has burned off by now. See what the input voltage to the three pole connector TPS is (should be around 4.6-4.8, most are). And then test the ground for resistance. See what your low voltage reading is throttle closed both to the TPS ground and chassis ground (back pin connector with the connector connected). The TPS adjustment is usually set up to the transmission side, the input voltages for the ECU side come from the ECU, for the transmission side from the TCU, sometimes they don't match very well. Just to see if anything is seriously out of wack. It's possible the ECU side of the TPS is way out. The ECU side of the TPS grounds through a few splices and ends up at the dipstick holder, as does the tranny side of the TPS, but the tranny side follows a different path. Check the ground rings at the dipstick holder for corrosion (oil and grease) and put them under the main ground cable.
There is an opening on the top of the TB, that goes from top to bottom, with the idle air bypass screw in the middle. It's possible it's gummed shut. If you have to remove the bypass air screw, count the turns, so you can install it back in the same position.
Block off all of the vacuum taps on the intake manifold and see what happens. The vacuum taps are all off center, so this can bias the O2 sensor readings.
Pull a couple of plugs, after a drive up the interstate at around 2000 RPM, this is usually the leanest running part of the RPM band and an indicator of the O2 function. Light grey (to off white) is good.
Double check your intake manifold bolts and the TB hold down bolts (the gasket shrinks).
Check the harness where it runs from the front of the fuel rail down the front of the motor. Hard to see in there, you may need a flashlight and a mirror. Mechanics have a bad habit of rerouting the harness after they do an exhaust manifold change or even a water pump change. The harness cooks on the exhaust manifold.
It may not be just one thing, it may be much like mine was and a bunch of small stuff, that added up to a really crappy idle.
Pull your MAT sensor out and clean the gunk of the end, carefully.
The reason for the laundry list is, this is what I did and noticed steady improvements at most every step. Mine idles great now, though just a touch low, around 500 RPM.
 
Ive done all of the things you have stated already. I changed the Manifold myself, so i made sure all the wiring and everything was put back in thier proper places. As stated above, i replaced my TB with one that i cleaned up really well. My concearn was though with that bypass air screw. When i took that TB apart to clean it all up, i just tightened that screw all the way down. I dont think that it plays a role, only because the idle is usually fine when not in gear. The IAC should make the proper changes. (I think)
The only thing i havent done and will try when i get a chance, is checking the ECU side of the TPS. Ive only checked/adjusted the TCU side, and made a ground jumper for it also.
 
I'd like to give you a definitive adjustment for the idle air bypass, but on the two TB's I have, one is screwed almost all the way in and the other is a full turn and a quarter out.
I'm thinking it's an individual setting for each motor. Likely a fine adjustment for minimum IAC opening.
I'd open it a quarter of a turn, see what the cold idle is and the hot (operating temp.) idle is.
If I remember correctly, I set mine for an idle of around 600-650 cold and then watched what the idle did when the motor warmed up. And turned it down a quarter of a turn each time I started the motor out cold again and it went through a warmup cycle, until it just started to affect the warm idle and then I stopped. It took more than a few tries.
When I had minimal change between the cold idle and the hot idle, the idle ended being a little low (warm), but not excessively so. Extended idle can throw the motor into open loop (idle changes yet again), so you have to be careful with the changes. Opening it up too far will just cause the IAC to close a little farther. What I'm trying to say (rather poorly) is there is a sweet spot, that can be hard to find. But unless your sensors (wiring/connectors/grounds/) are in order, adjusting the idle air bypass is likely wasted effort.
Each time you adjust the throttle stop, you have to readjust the TPS.
What shape is your air cleaner in, does taking the air cleaner element out affect the idle?
 
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8Mud said:
I'd like to give you a definitive adjustment for the idle air bypass, but on the two TB's I have, one is screwed almost all the way in and the other is a full turn and a quarter out.
I'm thinking it's an individual setting for each motor. Likely a fine adjustment for minimum IAC opening.
I'd open it a quarter of a turn, see what the cold idle is and the hot (operating temp.) idle is.
If I remember correctly, I set mine for an idle of around 600-650 cold and then watched what the idle did when the motor warmed up. And turned it down a quarter of a turn each time I started the motor out cold again and it went through a warmup cycle, until it just started to affect the warm idle and then I stopped. It took more than a few tries.
When I had minimal change between the cold idle and the hot idle, the idle ended being a little low (warm), but not excessively so. Extended idle can throw the motor into open loop (idle changes yet again), so you have to be careful with the changes. Opening it up too far will just cause the IAC to close a little farther. What I'm trying to say (rather poorly) is there is a sweet spot, that can be hard to find. But unless your sensors (wiring/connectors/grounds/) are in order, adjusting the idle air bypass is likely wasted effort.
Each time you adjust the throttle stop, you have to readjust the TPS.
What shape is your air cleaner in, does taking the air cleaner element out affect the idle?
Thats a good question! I have an XJ Armor (too bad Steve doesnt sell anything anymore...) 50 state legal intake tube with a 9" K&N. Ill have to see if removing the filter makes a difference.
As i said above i adjusted the "Stop" (For the throttle plate) to where the plate is open just enough to get a peice of paper through it. When i had the "Idle Air Bypass" screw off, i noticed it had an O-Ring on it. So even if i backed it off 1/4 of a turn would it still be able to get air through? Does everything else sound correctly adjusted?
Thanks for all your help man, its been benificial.
 
Muad'Dib said:
Thats a good question! I have an XJ Armor (too bad Steve doesnt sell anything anymore...) 50 state legal intake tube with a 9" K&N. Ill have to see if removing the filter makes a difference.
As i said above i adjusted the "Stop" (For the throttle plate) to where the plate is open just enough to get a peice of paper through it. When i had the "Idle Air Bypass" screw off, i noticed it had an O-Ring on it. So even if i backed it off 1/4 of a turn would it still be able to get air through? Does everything else sound correctly adjusted?
Thanks for all your help man, its been benificial.

If you open the idle air bypass and you get little or no change, you have to readjust the throttle stop and then the TPS again. I've got one TB where the throttle plate sits against the TB throat will very little clearance, the other has about .025-.030 clearance. Like I said, I believe the adjustment is individual for each motor and the sweet spot can be hard to find. The only writeup I've been able to find is a TSB from way back when.
Here is a TSB excerpt, part of another similar problem, cold motor stall. Installing the CPS wire kit and replacing the ECU was part of the fix for driveway stall outs. Along with the idle speed adjustment.

6tlxys4.png
 
Ok i think we are getting things mixed up. You stated in the post above that if i was to adjust the "idle air bypass" i would need to re-adjust the TPS. The TPS's position would not be changed by opening the "screw" that is on the lower portion of the tb on the drivers side (which is the screw i thought we were on the same page about calling "idle air bypass"). The throttle plate's "stop" (that is there only to supposidly stop the throttle plate from hitting the inside of the TB) would be the one that would effect the TPS if adjusted. Im not talking about messing with this "stop" only the idle air bypass.
For all i know, its supposed to be tight as i have it now... im uncertain on weither or not it even plays a role in the system...


EDIT!!!!

Sorry i read your post again, and i understand better.
 
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So do you think that adjustment would be a cure for the low idle? Would this cause more gas to be used?
Right now my gas milege is CRAP. Even with everything running well. (besides the idle of course) Im getting like 160-180 miles per tank in-town. I have the 19 gallon tank. So thats like what 9 miles per gallon.. YIKES!
 
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