Replaced TPS - Idle now WORSE!

[Ecomike]

Cruiser54 and I worked on one for the Renix TPS, that is very well written, but the 91-01 TPS is a little different. Renix had a pair of sensors in a sandwich, one operated the reverse of the other, and it need to be adjusted. Those are fun!!!!:laugh3:

91-01 TPS is not adjustable, has only one side, and 3 wires (instead of the 6 wires in the Renix years). But the testing method, hardware, and so on are the same. The idle voltage and WOT output voltage are in the FSM and old threads here (about 3.8V at idle and .2V at WOT IIRC, but I am not sure), and the input voltage from the ECU or PCM is 5.0 V (+/- .2V), and the third wire is ground.

http://www.naxja.org/forum/showthread.php?t=1072534#post245506765

http://www.cherokeeforum.com/f51/cruiser54s-mostly-renix-tips-153657/

The TPS is basically a carbon pile variable resistor, and as the carbon wears the signal gets noisy and you get bad data, jumpy signals that confuse the computer. You need an old style analog meter (best to get a high impedance analog muli meter, then you can live test the O2 sensor on the HO models, 91-01 as well) not digital, to see the smooth versus jumpy needle movement to detect a bad versus good TPS or O2 sensor. It needs to have an impedance of at least 20,000 ohms per volt, no less. There are a few threads here where several us beat to death the discussion of the analog high impedance multi meters choices (Volts-Ohms-Mili-amps, mulit-purpose).

 

[98xjeepy]

Xact wires for sure are junk. I was in mgnt. at advance for four years. I always told all my employees not to sell them if possible. Surpluses do fine. Have a set on my 98 going on two years no issues. Probably not the case but I had a bad miss and erratic idle that started about an hour after tune up. Ended up I tried every sensor new injectors, pressure regulator, and any other possible thing. It was a broken valve spring. More than likely not your problem but have you checked compression? I have terrible luck may be a long shot but it's a simple test.

 

[peuglow]

UPDATE:

Last night:
Removed IAC sensor, Cleaned Throttle body (wasn't bad at all)
Changed all plug wires
Changed all spark plugs (quick story, my old plugs were apparently really bad. Cracked, burned, huge gaps, etc so the new plugs will absolutely help the engine run better)
Tossed in a new air filter for kicks
Engine block ground looked fine

Arcing around the block/wires has ceased


None of this helped the idling. I even threw the old TPS on to see if the new one was faulty, did not change the idling from being all over.

What we DID find by luck - when the auxillary fan kicked on (we let her run for a few minutes to listen to the idle) the idle went back to normal. When the aux fan shut off, she idled all over the place again. So for kicks we turned the AC on, and the idle went back to normal. Turned the AC off, and immediately went back to seaching on the idle.

We also unplugged the MAP and it didn't seem to make the idle any worse.

So I'm thinking this is either a faulty MAP sensor, or a faulty IAC sensor. Going to the JY on Friday to pick up some gently used pieces. Any thoughts/observations before I do this?

 

[peuglow]

Also, I should add:

When I first replaced the plugs/wires/rotor and cat/muffler, I drove it for nearly 60 miles that night with no issue until the end of the run when she started sputtering/losing power at highway speed.

I don't think there is anything wrong with the CPS, as it has never had a hard time starting. Just bogging down/losing power when driving and searching when idling.

 

[Ecomike]

UPDATE:

Last night:
Removed IAC sensor, Cleaned Throttle body (wasn't bad at all)
Changed all plug wires
Changed all spark plugs (quick story, my old plugs were apparently really bad. Cracked, burned, huge gaps, etc so the new plugs will absolutely help the engine run better)
Tossed in a new air filter for kicks
Engine block ground looked fine

Arcing around the block/wires has ceased


None of this helped the idling. I even threw the old TPS on to see if the new one was faulty, did not change the idling from being all over.

What we DID find by luck - when the auxillary fan kicked on (we let her run for a few minutes to listen to the idle) the idle went back to normal. When the aux fan shut off, she idled all over the place again. So for kicks we turned the AC on, and the idle went back to normal. Turned the AC off, and immediately went back to seaching on the idle.

We also unplugged the MAP and it didn't seem to make the idle any worse.

So I'm thinking this is either a faulty MAP sensor, or a faulty IAC sensor. Going to the JY on Friday to pick up some gently used pieces. Any thoughts/observations before I do this?

Definately not the IAC, and the IAC is not a sensor, it is a control valve, Idle control valve. The fact that it idles fine with AC on confirms the IAC is fine. I doubt it is the map either. They rarely go bad and do not affect the idle, they do affect advance data input to the ECU when you move the gas peddle and change the engine vacuum!!!

 

[Ecomike]

Also, I should add:

When I first replaced the plugs/wires/rotor and cat/muffler, I drove it for nearly 60 miles that night with no issue until the end of the run when she started sputtering/losing power at highway speed.

I don't think there is anything wrong with the CPS, as it has never had a hard time starting. Just bogging down/losing power when driving and searching when idling.

Check the new spark plugs to see if any are already fouled with oil or black carbon (indicating a fuel injector or valve seal leak, or compression problem) now.

While a bad CPS will start out with these running problems before they die to a no start, hard start state, I don't think they cause idle hunting. Idle hunting is usually caused by an O2 sensor problem (bad fuse or relay on the power to the O2 sensor heater), or vacuum leak, or noisy TPS sensor. When the engine gets hot enough to turn on the radiator E-fan it may be switching to open loop (ignores O2 sensor) to run the engine cooler? The ECU also raises the idle speed when the AC is turned on.

 

[peuglow]

I should clear something up, I have not driven it with the new plugs. Just new plug wires/cap/rotor.

The current plugs have only run idling in driveway, no miles on them.


Sorry, I wrote sensor, meant valve on the IAC.

Any advice? I'm really stumped with this problem here and so is my buddy who's been helping me with diag this problem.

I haven't changed the CPS only because it hasn't had an issue starting. Could this be a symptom of a faulty CPS? Vacuum issue?

 

[Ecomike]

Could this be a symptom of a faulty CPS? Vacuum issue?

Could be any of a number of things. Try giving it a good hard highway drive with the new plugs, run some injector cleaner in the gas too. Then see what the plugs look like. Give it a good 50 mile trip.

Intake manifold bolts a little loose, vacuum hoses and tubes a little loose or broken, leaking can cause idle speed hunting issues. A bad MAT sensor (temp intake air temp sensor) has been know to cause idle speed issues.

Is the back tube from the valve cover to the intake manifold new or old and full crude, restricting air flow? It can starve the system for idle air if clogged up and cause hinting. Also a vacuum leak and working O2 sensor can cause hunting, or an injector leak can cause idle hunting, and so on.
So do a 100% leak inspection (search the older threads here for all the old war stories), And a working O2 sensor that is not getting power to the O2 sensor heater at idle will cause hunting!!!

 

[peuglow]

OK, I'll try to give her a drive tomorrow.

I put a bottle of injector cleaner in a week ago, so maybe that will help.

I'll check the back tube as well.

Before I changed the plugs, she was still bogging down when driving. That was the original issue that made me park it and open the hood. The plugs, wires, rotor, dist cap, TPS, cleaning the throttle body, messing with the MAP and IAC, have all been efforts to stop it from hunting.

I think I will also take the throttle body off to clean it tomorrow, just to make sure its nice and shiny.

Will advise as soon as I can. Thanks Ecomike.

 

[Ecomike]

OK, I'll try to give her a drive tomorrow.

I put a bottle of injector cleaner in a week ago, so maybe that will help.

I'll check the back tube as well.

Before I changed the plugs, she was still bogging down when driving. That was the original issue that made me park it and open the hood. The plugs, wires, rotor, dist cap, TPS, have all been efforts to stop it from hunting.

Will advise as soon as I can. Thanks Ecomike.

Bogging down at idle, or during acceleration? Will need to know if any bogging down during acceleration versus at idle before and after the drive. They are not the same!!

 

[peuglow]

Bogging down at idle, or during acceleration? Will need to know if any bogging down during acceleration versus at idle before and after the drive. They are not the same!!

Originally, the car was bogging down when driving (highway/backroads) Not necessarily during acceleration. During accel, steady pressure, etc. This occured out of the blue, and I parked it to avoid getting stranded.

Was told it could be a blocked cat. So I cut a hole before the cat to limp it home along with plug wires, rotor, and dist cap. Drove her home (5 miles).

Put a cat on and new muffler. Drover her almost 60 miles before she started bogging again (randomly and intermittenly). Parked her. Swapped out the plugs (they were REALLY bad) changed the air filter. Still searching in idle.

Don't know if it will still bog down when driving. But it has happened when the engine was cold in the first mile of driving, or with a warm engine after 60 miles of driving.

Has NOT stalled, has NOT had an issue starting.

 

[Ecomike]

At some point lets add a fuel pressure check if needed to the do list. Read a lot about fuel hoses in the gas tank coming loose lately on 90s jeeps. Some where first noticed on a bumpy road, and got worse over time. Seems you had multiple issues and fixed many already, maybe more than one left, LOL. They like to come in wolf packs, LOL, all at once, around the holidays

 

[peuglow]

Just finished cleaning the TB and the IAC Valve. I doubt they were creating any issues but they sure were dirty. Will perform all the other checks tomorrow/Friday.

 

[Peteyg]

Look for vacuum leaks. The rubber elbows can look ok and be leaking badly. All of the little rubber elbows and vacuum connectors on my '96 were toast and making the engine run very poorly.

Also, the running well when the AC is on is a big clue. The computer sends an idle signal to the TB to bring the idle up a little to compensate for the AC compressor. Coming off idle would smooth out an engine running poorly due to a vacuum leak. Also, a vacuum leak would cause the engine to run lean, which is bad for the cat and could cause it to fail.

Do you have a scanner that can read real-time data while it's running? You can check the operation of the MAP sensor. Make sure, also, that all of your electrical plugs and connectors are clean and making good contact.

Lastly....

I just got finished diagnosing a sudden death issue with my '96. It turned out to be the freakin' PCM case screws being too long, shorting the static shield to the circuit board and doing all kinds of bad things to the engine. Weird, undiagnosable electrical problems on the '96 could be related to this issue (it's also why, I think, it is so hard to find '96 PCM's in the Junkyard). It's something to look at, at least.

 

[Ecomike]

I just got finished diagnosing a sudden death issue with my '96. It turned out to be the freakin' PCM case screws being too long, shorting the static shield to the circuit board and doing all kinds of bad things to the engine. Weird, undiagnosable electrical problems on the '96 could be related to this issue (it's also why, I think, it is so hard to find '96 PCM's in the Junkyard). It's something to look at, at least.

That is one I have never heard of, very interesting.

 

[peuglow]

Thanks for the info. I'm thinking the vac leak is what I will look for next. I've never done it before so I'm hoping to find a thread to walk me through it. Will post a pic of the tb cleaning later

I do not have a scanner unfortunately. But the mech I go to would probably toss it on there for me.

 

[peuglow]

Here's the TB I cleaned. I had done it a few days prior without removing it from the intake, but after I put my son down last night I figured I'd pull it off and clean it, since it was just 4 bolts. I doubt the build up was enough to cause any issues. Also cleaned some junk out of where the IAC valve sits, and cleaned that valve well.

 

[heyhar]

Did you also remove the IAC chamber from the throttle body? You may be surprised at what lives in there. Just be very careful not to ruin the thin gasket if you do pull it off.

 

[peuglow]

Did you also remove the IAC chamber from the throttle body? You may be surprised at what lives in there. Just be very careful not to ruin the thin gasket if you do pull it off.

I did not remove it, only because I didn't have the torx bits with the safety pin cut in (I can't remember what it's called)

I did jam a toothbrush in there with plenty of cleaner, and then wrapped a rag around the other end of the toothbrush to wipe it clean. Looks much better than it did. Here's the after. Not the best picture.

To be honest, I'm not optimistic about this improving my idling issue, but it sure as hell can't hurt. (not sure if the plug wires/new plugs fixed the intermittent/random bogging issue, will test drive tonight.)

 

[heyhar]

Some years have the 'tamper proof' Torx screws, some don't. I did my '96 a year ago, and was amazed at what was in there. Especially considering that it's only air, not an air/fuel mixture that passes through there, as in a carb. I got a set of 'tamper' bits at Harbor Freight for a few bucks.