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cleaning an XJ throttle body?

Did the TPS check with a multimeter. Here's what I got:
Key on.
Voltage at A (5.0V supply) pin (with TPS connector disconnected.) is 5.05V.
Voltage at B pin (with TPS connector disconnected.) is .05V.

Also, key on. Connector connected. Throttle plate closed.
Voltage at B (ground) pin: .05V
Voltage at C (positive) pin: .64V

From what I was reading, it should be around .8V. If so, TPS is good.

The voltage smoothly increased when moving the throttle open slowly, from .64V at idle to 4.42V WFO throttle with multimeter probe in C port with plug connected.

Tip #8 says to get values for A, B, and C, to check on the adjustment, and I have those as well.
A: 4.94V
B: .05V
C: .64V
But I'm confused about what to do with these numbers. It says to "note A & B. This is your reference voltage." Huh? is it A or B?

Also "note B and C. This is your OUTPUT voltage." Huh? Is it B or C?

Also checked the MAP sensor...sorta. With the key on, the L sensor showed 5.06V. The center probe showed 4.72V. I did not turn the key on to check the vacuum though, or have a mitivac to do more than this though.

I checked all the ground terminal connections as well. All are clean and dry. High idle still exists.
 
It's A and B. One is voltage and the other is ground. Leave the connector together and back probe.

And, as I've said now numerous times, do 1 through 5 FIRST, as you may have another issue affecting those readings.

READ Tip 1!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
Ok. A and B. So A (4.94) x .17 (the 17%) =.8398 volts. Which tells me.....what exactly? I don't know what it should be, if this is high or low or....whatever. There's no reference for this at point #8.

Where does B come in then? Or C?

Again, 1 thru 5 are done.
 
wgregt said:
Ok. A and B. So A (4.94) x .17 (the 17%) =.8398 volts. Which tells me.....what exactly? I don't know what it should be, if this is high or low or....whatever. There's no reference for this at point #8.

Where does B come in then? Or C?

Again, 1 thru 5 are done.
Click to expand...

It tells you that your output voltage is 17% of your input voltage, which is what it's supposed to be. Every Jeep can be a bit different.

Now, if Tip 5 showed low resistance and it didn't change when the harness was wiggled, and the dipstick grounds are sparkling clean and tight, your TPS is bad on the engine side, provided the IAC is good.

In Tip 2, what did the inside of the C101 look like?

It might not be a bad idea to do Tip 27 in it's place.
 
8Mud said:
I've had the best results using a propane torch with no flame, just spewing propane near suspected leaks. A lot less of a fire hazard than spraying flammables around the engine bay. And actually works better than fluids checking for injector O ring leaks.

If you use starting fluid or carb cleaner wear your safety glasses and keep a fire extinguisher handy. I worked a second job in an auto crafts center for most of a decade, somebody would loose most of their hair just about once a week.
Click to expand...


I couldn't agree more. Propane or mapp gas.
 
Tip # 5 did show low resistance (.05V) and did not move when I wiggled the hell out of the whole harness, even going up to the MAP sensor. Dipstick ground is good and tight. The IAC is good in that it's clean...not sure there was any way to tell anything else. It was clean when I pulled it out, and the bore is clean as well. Seriously, I did not get anything on a white shop towel when cleaning it.

So what do you mean the TPS is bad on the engine side? I thought the numbers checked out OK...no?

I expected worse inside the C101, but it was dry, ad only a few sections had anything to clean out (I have cleaned this in the past...like 5-6 years ago maybe.)

Right now I'm thinking of having a flatbed take it to the dealer this week. I could drive it, but it is a bear to drive like this. The brakes are good, but they barely hold, and it creeps when stopped even with me standing on the brake pedal. I don't want to let the dealer take a crack at it, but I've checked just about all I know to check at this point.
 
wgregt said:
Tip # 5 did show low resistance (.05V) and did not move when I wiggled the hell out of the whole harness, even going up to the MAP sensor. Dipstick ground is good and tight. The IAC is good in that it's clean...not sure there was any way to tell anything else. It was clean when I pulled it out, and the bore is clean as well. Seriously, I did not get anything on a white shop towel when cleaning it.

So what do you mean the TPS is bad on the engine side? I thought the numbers checked out OK...no?

I expected worse inside the C101, but it was dry, ad only a few sections had anything to clean out (I have cleaned this in the past...like 5-6 years ago maybe.)

Right now I'm thinking of having a flatbed take it to the dealer this week. I could drive it, but it is a bear to drive like this. The brakes are good, but they barely hold, and it creeps when stopped even with me standing on the brake pedal. I don't want to let the dealer take a crack at it, but I've checked just about all I know to check at this point.
Click to expand...

.05V is not a resistance reading.

The C101, even though cleaned, can cause issues.

The dealer won't know what to do with it since it's pre-OBD.

The dipstick tube grounds can LOOk good, be tight, but still cause these issues. You didn't clean them, did you?
 
The local dealer has a tech who is a grand master tech, who runs the local Jamboree each year, and has a ton of press/articles/etc in all of the last off road mags for probably 20+ years or so. He's got an 87 XJ with 680K last time I saw the odo with my own eyes. I'm sure he could solve it, but I'd like to solve it myself first if possible.

Could you tell me what you mean by the TPS is bad on the engine side and I'll re-check it. Or maybe you're saying I need a new TPS? I'm unclear.

I did clean the dipstick grounds. Used the cordless dremmel actually. I can't see how it could be a ground issue there.
 
wgregt said:
The local dealer has a tech who is a grand master tech, who runs the local Jamboree each year, and has a ton of press/articles/etc in all of the last off road mags for probably 20+ years or so. He's got an 87 XJ with 680K last time I saw the odo with my own eyes. I'm sure he could solve it, but I'd like to solve it myself first if possible.

Could you tell me what you mean by the TPS is bad on the engine side and I'll re-check it. Or maybe you're saying I need a new TPS? I'm unclear.

I did clean the dipstick grounds. Used the cordless dremmel actually. I can't see how it could be a ground issue there.
Click to expand...

You are very fortunate to have a tech with that wealth of ecpeerience at your disposal.

So, now I know you completely did the Tips.

You are working on the Engine side of the TPS if you're using the flat 3 wire plug. Renix TPSs have 2 "senders" in them. One id for the engine and one is for the Trans. They work opposite of each other. One side can be bad while the other is bad.

Does the Jeep ALWAYS idle between 1800 and 3000? Is it something new? Does it sometimes work perfectly?

Is your throttle linkage not binding? Has anyone ever messed with the throttle stop screw?
 
No, it's not always been like this. It does come and go though. It's not a daily driver: I only drive it when it rains here in SoCal (otherwise I'm on one of the motorcycles.) So, I drive it....5-6 days a year for commuting then? Add in another week or so of errands, and it doesn't get a lot of use like it once did. Thing is sometimes it idles high and will slowly come down on it's own once I get on the freeway and do 5-10 miles or so.

And other times it won't come down for a solid day of commuting.

And sometimes it runs/starts fine.

This time seems exceptionally high idle, and it's been like this for....a while now.

No one has messed with the throttle stop screw. I was told/read here that it's a "no touch" setting from the factory. So..I have not touched it. Plus, in my mind I would think that's only a "quick fix" that may fix it, but doesn't tell me what caused it, since I'm assuming that screw can't move on it's own.

The linkage, when I moved it thru the idle to WFO arc while hooked up to the multimeter, worked smoothly in both directions with no binding or tightness.

Are you thinking a new TPS would be something to try?
 
I'm not advocating messing with the stop screw by any means. Just trying to get a clear picture of what's going on.

This shows all the classic signs of a bad TPS or a problem in the ground circuit to the TPS and other sensors.

Since you've completed Tip thoroughly and not experienced any variations in ohms readings even when wiggling,

So, this leaves a bad TPS or poor signal through the C101.

There is no downside to eliminating the c101 per Tip 27. I've seen numerous different gremlins cured by doing so.

You could try a new TPS. How old is the one on there anyway? Decades old?
 
Good question. I looked thru all my paperwork (I bought this new in 88) and did not see anything where I have replaced the TPS. I surely have never done so myself, so it would have come from a dealer tech install, or maybe some other mech shop.

I have had it in the shop various times over the years for this high idle issue though with various things done to fix it, I'm sure. I cannot believe it is the OEM one with....almost 300K on it. My guess is it's been swapped out, and I have lost the paperwork for it somewhere for now. I KNOW I have not had a new one installed since 05 for sure, as those records I know are correct.

OK. So....where to buy one? OEM? NAPA? Does price make a difference in quality? How long/how many miles is a new TPS supposed to last....and BTW what makes them go bad? Any idea how much the dealer OEM one goes for? If it's a lot I know I could rule out getting one there cause I'd know by the price that I had not spent that much money at the dealer recently.
 
One thing that confuses me is this: if the TPS IS bad, I'd love to see a test that shows a good/no good value. Am I wrong that it seems to be a bit of witch-doctory voodoo that determines CLEARLY if the TPA is bad or not? No offense to you and your very helpful patience and advice, but overall (from reading other posts) I get the feeling that replacing it seems to be a sort of "Well.....we've tried most other major things, so go ahead and swap in a new TPS and see what happens."

Is there not a clear go/no go check?
 
i Had one that gave a different reading most every time I tested it. Turned out to be WD-40 inside the connector.

I had one that would periodically screw up, turned out to be an iffy splice in the ground circuit.

Had another would cause an occasional idle around 3000 RPM, happened shortly after I did a motor wash. That was when I figured out that TPS aren't sealed well.

Had another that acted up after I got a little wild with the brake cleaner while cleaning my throttle body.

Had another where the motor would fall flat on it's face just about anytime I tried to slow speed drive through the neighborhood. There was one small spot in the TPS that was dead, a tiny glitch that was really hard to spot.

Changing out the TPS isn't that big of a deal as long as you get the screws out the first time and grease them when remounting the TPS for next time. Keeping a spare for testing can save a lot of time and effort chasing ghosts.

I spent many hours looking for that bad splice and actually found it by accident after ohm testing the circuit multiple times.

One of those parts that is much easier to slap in a known good part and see if that fixes it, if not you have to start digging deeper, maybe unraveling major harnesses. Digging in deeper can cause issues all it's own, many of the wires and connectors are decades old and are prone to being brittle.

Most times I ohm test the TPS ground circuit, check the input voltage and do a sweep test. An analog meter works best for a sweep test as many digital meters react a little slow, it can be hard to tell the difference between a dead spot and poor contact (wiggle) on the test leads. I learned to test before and after the connector.

I'm not a fan of just swapping parts out and hoping for the best, but having a spare set of sensors, TPS, MAP, CPS, relays, ECU etc. can sure be a time saver when trouble shooting. I got my spare set out of a rolled Renix and keep it in a small tackle box in the back of my XJ.

I'm not a master XJ tech, but I am a master machine troubleshooter. What makes me a master troubleshooter is I never give up. I usually troubleshoot form easy to difficult, then troubleshoot from one end to the other (or from the middle out).

I got my last Renix XJ from a major Jeep dealership, they had given up on it and almost paid me to take it away. :)

One thing I found odd about yours is the TPS input voltage you posted was higher than I'd ever seen in a Renix.
 
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Check and see if there is any gap between the throttle plate and the TB bore. Check with the motor stopped and running. The throttle plate should be closed at idle, that is when the IAC has control over idle. There may be a tiny gap. like the thickness of a piece of paper, this is normal.

If you ever do get a decent idle again, unplug the IAC, take it out of the equation. Starts may require a little gas pedal feathering and during the warm up period the motor *may* want to stall or stutter when you release the gas pedal suddenly, but other than that it will run without it.

One thing I did find on my newest to me Renix was the ground for tranny half of my TPS was swapped with the ground for the motor half of the TPS. One of those WTF moments when I eventually figured that one out.

I'm out of ideas, for the moment. :)
 
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Only a few reasons I can think of for a 3000 RPM idle. It is getting too much air for some reason when it shouldn't be. Vacuum leak, either a vacuum line, the manifold, the TB itself or an IAC issue. Unlikely but possible the throttle plate is wrong. The TB gasket can shrink or crack and/or the TB mounting bolts can come loose.

The TPS. If you reach behind the TPS with a thin screw driver you can move the arm on the TPS and the idle will go up as the arm moves.

Remotely possible you are getting too much fuel, but unlikely. Too much fuel and not enough air will choke the motor in most cases. Unlikely to get just the magic amount of extra fuel to raise the idle much without causing the motor to lope and idle really bad. It's a fine line between just enough and too much.

The O2 sensor may be giving faulty info, never seen one cause a 3000 RPM idle. But if you are getting desperate unplug it and see what happens.

Most likely is too much air at idle for some reason, the TPS or an electrical fault.

Just for giggles loosen the TPS, move it a little both directions and see what happens to your idle. Set it at .08 and check the output voltage, watch the little arm and see if it maxes the output voltage before the throttle is fully open, It may be giving the right voltages, but at the wrong places, the ECU is dumb and may not have an an answer for the values it is receiving. You can look down the IAC inlet and see the piston moving as you work the throttle with the engine idling. If it is all the way open and not moving, you likely have an open circuit in one of the IAC feed wires, maybe a faulty IAC. The injector harness has a TSB out for possible wire fatigue near the bend at the firewall. I really can't remember if the IAC pigtail goes through or around that harness, whichever, a fatigued wire is a possibility. One broken or really frayed wire may only allow the piston to move in one direction, in your case open. The bad thing about a fatigued wire is it can be under the insulation where you can't see it. A single strand (or a few strands) of wire can still be connected and may ohm OK, but won't pass enough amperage to work the IAC. The IAC needs all the electricity it can get, a healthy charging system and battery. Current issues usually show up as the IAC sticking closed, but I doubt I've seen every possible scenario. The way I check for fatigued wires is to squeeze every inch of a suspect wire between my forefinger and thumb, you can feel where the wire is frayed under the insulation. Connectors have to be ohm tested and eyeballed.

The reason there are four wires going to the IAC, is that it is a reversible motor. Possible the IAC is only working in one direction, in your case opening. The IAC wires do go through the C 101 connector (which was mentioned) as another likely spot for trouble.


bild hochladen

Kind of grasping at straws here, but you've tried the more common possibilities.

I'm multilingual and sometimes get my nouns and verbs reversed, screw up the spelling or use some strange syntax. If I need to clarify anything let me know.
 
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