Renix high idle

[slowrider]

Little help please. My 87 4.0 MJ was idling slow and rough so I cleaned the throttle body ( which was really nasty) and now it idles smoothly but very fast. Any suggestions as to what might cause this? Any help would be appreciated.

 

[8Mud]

My IAC was stuck closed and somebody had adjusted the throttle stop to compensate. When I cleaned the IAC, it idled pretty high.
Is your IAC stuck open? If you removed it, did you get it to seat flush or is the "O" ring twisted up some.
Did you knock off a vacuum line, when you were doing the job or break one of the plastic vacuum lines?
if you took off the TB, did you use a new gasket? If you re-used the old gasket, did you get the gasket exactly in the original position.
Vacuum leaks or a stuck open IAC (which is actually rare, they usually stick shut), are usually the chief causes of a high idle.

 

[slowrider]

My IAC was stuck closed and somebody had adjusted the throttle stop to compensate. When I cleaned the IAC, it idled pretty high.
Is your IAC stuck open? If you removed it, did you get it to seat flush or is the "O" ring twisted up some.
Did you knock off a vacuum line, when you were doing the job or break one of the plastic vacuum lines?
if you took off the TB, did you use a new gasket? If you re-used the old gasket, did you get the gasket exactly in the original position.
Vacuum leaks or a stuck open IAC (which is actually rare, they usually stick shut), are usually the chief causes of a high idle.

Thanks for the ideas. I checked the vacuume lines and the gasket but not the IAC, mostly because I'm not sure what IAC stands for Another item a freind told me to check was the TPS (that one I recognised) I'll try the TPS tomorrow and if I can figure out what the IAC is I'll check that too.

 

[BIGSLVRXJ]

If you left the TPS on while cleaning it you may have ruined it. Get a lifetime warranty Borg-Warner one if thats the case(fry em all ya want.) The IAC is your Idle Air Control Motor. It's located right next to the TPS.(the sensor closer to the passenger side on the TB.) You can adjust the idle stop if needbe but you will need to adjust the TPS afterwards.
HTH,
Collin

 

[Dirt]

Idle Air Control valve that's what controls your idle speed by allowing more or less air into the throttle body. it's on the throttle body a round thing with three wires i think

 

[XJXJ]

Idle Air Control valve that's what controls your idle speed by allowing more or less air into the throttle body. it's on the throttle body a round thing with three wires i think

Close, it's actually 4 wires because it's a bi-polar stepper motor driven from the ECU. You've gotta get the TPS adjusted AFTER setting a HOT throttle plate idle RPM with the IAC fully closed. Then adjust TPS per spec and go from there. Sometimes the IAC is at fault but other things will affect idle like 02, temp sensors, latch relay and a few other things.

You can pull the IAC out, leave it connected and watch it while switching the ignition on/off. If it moves, it's probably okay. Another way is to simply pull a small vac hose and listen for the RPM to settle back after a few moments. Or, touch the brake power booster and the sudden loss in vacuum will usually cause the IAC to move a little too but that's very subtle to notice with the engine running.

 

[old_man]

Here is a pix to help. High Idle is normally caused by a vacuum leak, but since you were messing with the TB, go ahead and clean the IAC and the orifice inside.

 

[8Mud]

You can pull the IAC out, leave it connected and watch it while switching the ignition on/off. If it moves, it's probably okay. Another way is to simply pull a small vac hose and listen for the RPM to settle back after a few moments. Or, touch the brake power booster and the sudden loss in vacuum will usually cause the IAC to move a little too but that's very subtle to notice with the engine running.

If you did that, you got really lucky, Jeep has a tool, to keep the piston from flying out the end of the motor, when testing under power. I had a brain fart and tried just what you suggested once and the plunger from my IAC lauched itself about 15 feet across the driveway. The book says if the piston is seprated from the motor, it´s a throw away, I´ve carefully put the piston back in and had it work fine, though I did, move it to the toolbox for a spare and put my spare in the Jeep.

 

[slowrider]

I'm learning alot about the renix here thanks guys. I've been going through these suggestions and I haven't found it yet. I cleaned the IAC and re installed it and the idle dropped a bit but not nearly enough so I replaced it without change in the idle, I did the visual verification of the IAC and it works. How does cleaning the TB effect the TPS? to clarify "cleaning the TB" I hosed the butterfly and throat with Chemtool and wiped it out with a new rag, I didn't remove it and open it up so I cant see how I could have hurt the TPS but thats my next item to replace. How possible is it that the chemtool got into the small passeges and broke something loose? I did find the small vacuume line on the side with 2 couplers close together and the other hole in the rubber vacuume reciever wide open but plugging the open one and replacing the spliced line didn't effect it. Pulling a vacuume line off made it idle higher. Thanks again and keep those ideas coming.

 

[old_man]

I think you were describing the vacuum line that runs to the MAP sensor. One of the holes supplies the vacuum, the other is a blind hole. Make sure you have the hose plugged in the right one.

 

[slowrider]

I think you were describing the vacuum line that runs to the MAP sensor. One of the holes supplies the vacuum, the other is a blind hole. Make sure you have the hose plugged in the right one.

Sounds right. What I'm talking about is rubber, is on the passenger side of the TB and has two ports. On mine the lower one had a vacuume line leading to a control on the firewall (MAP sensor?) and the top one was open. I replaced the existing line and plugged the upper one.

 

[8Mud]

Most times the throttle plate (butterfly) sits flush with the sides of the bore, there is no gap (or very very little). On the drivers side of the TB there is a lead cap, under the lead cap there is an adjustment for the idle (if the orifice isn´t gummed shut). If the throttle plate is all the way closed and the lead cap is in place, it´s probably not the TB and is a vacuum leak someplace.
I wouldn´t adjust anything on the TB, until I´ve found and fixed the problem. There actually isn´t much at the TB to adjust to lower the idle, if it is at factory settings.
A bad O2 sensor will often, cause the idle to fluctuate (up and down) a couple of hundred RPM´s (also sometimes a very small vacuum leak will do the same).
Try unpluging the vacuum lines one at a time and plugging the nipple on the intake with your finger and see what happens.
If your idle is at 1500 RPM´s that´s almost always the major vacuum line near the rear of the intake, thats open someplace or has fallen off of your vacuum canister.
800 or 850 actually doesn´t work bad for an idle, thats where I set mine, I often idle and talk on the radio, noticed my battery would slowly discharge at around 500-650 RPM`s, it stays charged at 800-850.
Does your idle change with the motor temp.?
Is your A/C on?

 

[slowrider]

Most times the throttle plate (butterfly) sits flush with the sides of the bore, there is no gap (or very very little). On the drivers side of the TB there is a lead cap, under the lead cap there is an adjustment for the idle (if the orifice isn´t gummed shut). If the throttle plate is all the way closed and the lead cap is in place, it´s probably not the TB and is a vacuum leak someplace.
I wouldn´t adjust anything on the TB, until I´ve found and fixed the problem. There actually isn´t much at the TB to adjust to lower the idle, if it is at factory settings.
A bad O2 sensor will often, cause the idle to fluctuate (up and down) a couple of hundred RPM´s (also sometimes a very small vacuum leak will do the same).
Try unpluging the vacuum lines one at a time and plugging the nipple on the intake with your finger and see what happens.
If your idle is at 1500 RPM´s that´s almost always the major vacuum line near the rear of the intake, thats open someplace or has fallen off of your vacuum canister.
800 or 850 actually doesn´t work bad for an idle, thats where I set mine, I often idle and talk on the radio, noticed my battery would slowly discharge at around 500-650 RPM`s, it stays charged at 800-850.
Does your idle change with the motor temp.?
Is your A/C on?

Well I don't have AC so thats not it. I've checked the vacuume system over and over and I haven't found much (not that there isn't a problem). Just in case I changed the O2 sensor and NOW the idle is fluctuating where it wasn't before. The lead plug is in place on the TB. A buddy of mine said to reset or clear the computer but he wasn't absolutley sure how to do it . He thinks you disconnect the posative battery cable and hold the key in the crank position for 15 seconds and then start it and let it idle for 15 Min.Anyone know if that's correct for a renix? . I'm going to try a reset and if that doesn't work maybe do a real TB cleaning. Thanks again.

 

[XJXJ]

Well I don't have AC so thats not it. I've checked the vacuume system over and over and I haven't found much (not that there isn't a problem). Just in case I changed the O2 sensor and NOW the idle is fluctuating where it wasn't before. The lead plug is in place on the TB. A buddy of mine said to reset or clear the computer but he wasn't absolutley sure how to do it . He thinks you disconnect the posative battery cable and hold the key in the crank position for 15 seconds and then start it and let it idle for 15 Min.Anyone know if that's correct for a renix? . I'm going to try a reset and if that doesn't work maybe do a real TB cleaning. Thanks again.

Curious, does an '87 with no AC even have an e-fan?

Very few KAM codes stored in Renix. It doesn't hurt to clear 'em but I don't think it matters much. Just pull battery power with the key-on for a few seconds.

You're gonna need to qualify the system one step at a time.

 

[Cesar]

I hade a similar problem with my 88 XJ, the thing that solved it was removing the big cable conector at the firewall by splicing the wires, this connector was only used in a couple of years on the jeeps and was discarded because it caused a lot of problems due to corrosion on the terminals.

 

[old_man]

Probably one of my most valuable diagnostic tools is very uncommon in most people's tool boxes anymore. It is a vacuum gauge. You can buy them for less than $20. It is a great tool. Hooking it to your intake can tell you tons about the health of the engine. Many of the vacuum gauges can also be used for a pressure gauge to measure fuel system pressure as well.

With a vacuum gauge, you can tell in a minute if the problem is a vacuum leak related problem or a computer related problem.

 

[Bender]

What is the vacuum supposed to be at idle?

How does the vacuum guage tell you if your problem is vacuum related or not? Wouldn't a sensor problem cause the IAC to open slightly which would read the same as a vacuum leak?

 

[georgemu]

What is the vacuum supposed to be at idle?

How does the vacuum guage tell you if your problem is vacuum related or not? Wouldn't a sensor problem cause the IAC to open slightly which would read the same as a vacuum leak?

CONDITION INDICATION
readings are at idle unless otherwise stated. Gauge readings are in inches
1. Normal Steady at 15 to 21
........................
Drops to 2, then rises to 25 when throttle pedal is rapidly depressed then released.
2. Intake leak Low steady reading less than 10
3. Head gasket leak Gauge floats between 5 and 19
4. Improper idle mixture floats slowly plus or minus 1 ½ to 2 ½ inches
5. Small spark gap or defective points slight float plus or minus 1 to 1½ inches
6. Late ignition timing Approx 2 inches below normal idle
7. Late valve timing 4 to 8 inches below normal idle
8. Worn valve guides Oscillates plus or minus 2
9. Weak valve springs Violent oscillation (plus or minus 5 inches) as rpm increases. Often steady at idle.
10. Sticking valves Normally steady, will intermittently flick downward about 4 inches
11. Leaky valve Regular drop about 2 inches
12. Burned or warped valve Regular, evenly spaced down-scale flick approx 4 inches
13. Worn rings/ diluted oil Drops to 0, then rises to approx 18 when throttle is rapidly depressed then released
14. Restricted exhaust system Normal when first started. Drops to 0 as rpm increases. May eventually rise to approx 18

 

[Bender]

Would a stroker motor read higher vacuum?

 

[slowrider]

Curious, does an '87 with no AC even have an e-fan?

Very few KAM codes stored in Renix. It doesn't hurt to clear 'em but I don't think it matters much. Just pull battery power with the key-on for a few seconds.

You're gonna need to qualify the system one step at a time.

You're right there isn't an e fan yet (I have one coming in the mail) Well I tried clearing the codes and it didn't help so I pulled the IAC and the piston is the same size as the original one but the barrel around it has a thinner wall so I'm wondering if thats causing an air leak.