TPS problems (Got 2 sensors, same problem)

[mattbred]

Have you tried letting it idle from a cold start to fully warmed up with the TPS disconnected to see what the idle does. Then very slowly give it some gas to 2000 rpm then slowly return it to idle? (do it slowly or it will probably backfire, hesitate and die with out the TPS connected). The idea being to see if the idle changes with out the TPS attached.

Alrighty I just tried it.

With out the TPS connected, the jeep idles to 900-950 after warming up.
Anything I rev it to, it drops back down to 900-950.

I put the TPS back in, and it idles at 900-950, and anything I revved it to it stays at 900-950.

You know, my friend drove it last night and said it idled at 900, not ever reaching 1300. What I did was reattached the ground wire from the TPS to the ECU ground, before I had a completely seperate ground going to the engine block. I also reset the TPS to 0.79 volts. Maybe that fixed it? I still would like to test the voltages at the ECU.

The shop I took it to awhile ago said they couldn't find any vacuum leaks. Wonder why it idles at 950. When cold it idles at 650 then progressivley gets higher and higher. I also replaced my throttle body gasket, and all the top bolts and two of the under bolts on the intake manifold are right tight. (He rebuilt the engine 50,000 kilometers ago) so I doubt that's the problem.

 

[Ecomike]

The silver/aluminum colored, cast aluminum housing is the ECU, the one that says BENDIX!.

The yellow one is the cruise control computer controler. Don't recognize the transparent plastic box, an alarm system perhaps?

What one of these is the ECU?

(Btw that black box says "Bendix").

 

[Ecomike]

900 to 950 is not bad, but it should be about 750 in park, and about 600 in drive both at idle shortly after warm up.

Sounds like you should stick with the working ground set up that is holding it at 900 to 950 RPM. It is critical for the TPS and the ECU to see the same exact ground potential!

Based on that test, it sounds like there is either still a tiny vacuum leak, or the IAC is not working the entire stroke length (did you oil it after cleaning it?). Be careful with it, do not force it to move in/out manually as you can damage it permanently!

If, and I mean IF, it is definately not one of those two (vacuum leak or IAC malfunction), then the prior owner(s) may have messed with the throttle stop ear, or throttle stop screw setting, or the hidden air setting on the side under the seal/cap on the side of the throttle body, or some trash could be in the way holding the IAC too far open, keeping it from closing more.

You definately have an rpm that is 200 rpm too high that is not caused by a TPS or TPS ground issue based on that test. The difference between 950 and 1300 must have been the tps ground issue you just solved.

Alrighty I just tried it.

With out the TPS connected, the jeep idles to 900-950 after warming up.
Anything I rev it to, it drops back down to 900-950.

I put the TPS back in, and it idles at 900-950, and anything I revved it to it stays at 900-950.

You know, my friend drove it last night and said it idled at 900, not ever reaching 1300. What I did was reattached the ground wire from the TPS to the ECU ground, before I had a completely seperate ground going to the engine block. I also reset the TPS to 0.79 volts. Maybe that fixed it? I still would like to test the voltages at the ECU.

The shop I took it to awhile ago said they couldn't find any vacuum leaks. Wonder why it idles at 950. When cold it idles at 650 then progressivley gets higher and higher. I also replaced my throttle body gasket, and all the top bolts and two of the under bolts on the intake manifold are right tight. (He rebuilt the engine 50,000 kilometers ago) so I doubt that's the problem.

 

[jeeperjohn]

I had a Mustang that would idle high because I had a 160* thermostat in it. It was staying in warm up mode. Putting in a stock temp t-stat made it idle properly.

 

[Saudade]

Don't recognize the transparent plastic box, an alarm system perhaps?

It's the emission timer. Mine's gone too.

 

[Ecomike]

It's the emission timer. Mine's gone too.

Awfully complicated looking gadget for just a timer. Guess I was close with the alarm system guess. :explosion

 

[ren]

All of my stuff still has them, their just unplugged. Anybody want one? According to the FSM, they are one-time use and then replace anyway. All the did was let you know that it was time to replace the O2 Sensor.

 

[mattbred]

900 to 950 is not bad, but it should be about 750 in park, and about 600 in drive both at idle shortly after warm up.

Sounds like you should stick with the working ground set up that is holding it at 900 to 950 RPM. It is critical for the TPS and the ECU to see the same exact ground potential!

Based on that test, it sounds like there is either still a tiny vacuum leak, or the IAC is not working the entire stroke length (did you oil it after cleaning it?). Be careful with it, do not force it to move in/out manually as you can damage it permanently!

If, and I mean IF, it is definately not one of those two (vacuum leak or IAC malfunction), then the prior owner(s) may have messed with the throttle stop ear, or throttle stop screw setting, or the hidden air setting on the side under the seal/cap on the side of the throttle body, or some trash could be in the way holding the IAC too far open, keeping it from closing more.

You definately have an rpm that is 200 rpm too high that is not caused by a TPS or TPS ground issue based on that test. The difference between 950 and 1300 must have been the tps ground issue you just solved.

Well when I took the IAC out, I twisted it but never forced it in or out. Just turned it a bit. I also sprayed some throttle body cleaner down there.

Today I took it out and put in some oil, then "MoveIt" (WD40 like stuff) and will put some more oil in it tomorrow. I accidently dropped one of it's bolts into the nooks and crannies of my engine bay, never to be found again, too. Anyone know exactly what size bolts they are?

Also, if you messed with the throttle stop, that wouldn't cause a steadily increasing idle would it? that would just cause a constant idle. It's as if a temp gauge isnt working (which they are as far as I know), or a gasket is leaking.

 

[Ecomike]

Well when I took the IAC out, I twisted it but never forced it in or out. Just turned it a bit. I also sprayed some throttle body cleaner down there.

I have never tried this (yet), but it would be interesting to cycle the power on 10 seconds and off 10 seconds with out starting the engine, while the IAC is disconected mechanically, but electrically connected to see if it moves at all? I don't know just how sensitive these guys are to being forced to move or turn.

Also, if you messed with the throttle stop, that wouldn't cause a steadily increasing idle would it? that would just cause a constant idle. It's as if a temp gauge isnt working (which they are as far as I know), or a gasket is leaking.

Depending on which way it was bent or moved, yes it would be a steady increase (decrease), except that the IAC might be able to compensate some in one direction (decrease) and not the other (increase). From the sound of it I am thinking you have a bit of both problems, some steady high idle plus some slowly rising high idle.

What makes these problems so difficult to diagnose is that many times there are several causes at the same time of an idle problem (or any problem), then on top of that the computer is busy trying to compensate for the problems when and where it can.

 

[mattbred]

Alright I'll look into it. Another thing I forgot to say when I was diagnosing stuff was that the books I have say that the distributor should be getting 5 volts from the bottom connector, right? Mine get's 7 volts. Is that somethin to worry about?

 

[mattbred]

Well shite. After driving it around today, it's back idling at 1300-1400. If I quickly and agressivley tap on the gas pedal, it goes back to 1000.

 

[Ecomike]

Alright I'll look into it. Another thing I forgot to say when I was diagnosing stuff was that the books I have say that the distributor should be getting 5 volts from the bottom connector, right? Mine get's 7 volts. Is that somethin to worry about?

You might want to post that question in a new thread, like "distributor voltage, 7 Volts?" I don't have that handy in any of my reference materials but some one here should.

 

[mattbred]

Aha so it isn't the TPS after all that's causing me high idle. It cant be. It was idling at 1300 and I moved its lever really fast and such, with the end result being the same high idle. pushing hard on the throttle cable-lever thingie against the throttle-stop made RPM's go down by 200-300ish however. The thing that's weird, is that shutting it off and restarting it fixes it for the moment. Resetting IAC maybe? I'll try and grease all my linkage up and flatten the stop up as well. Perhaps it was moved. Any way to check?

 

[cygnus58]

I have a question about checking the TPS.
With two seperate TPS, if I check them off the engine, still connected, everything checks normal. (5v in, <1v to 5v out depending on lever position, and smooth.
When I screw it onto the throttle body, the output voltage stays at the low end, and doesn't vary.
There is a ground made on the bottom screw, but there is no continuity between that ground and either the lever, or ANY of the terminals in either of the two plugs. Why mounting it would change the out voltage baffles me.
I have had a bucking/coughing problem at over 2900 rpms and was trying to rule out the TPS.
Also , I can't find any mention anywhere as to the significance of the "second" plug...one is 4 pin, and one is 3. Are they simply in parallel?

 

[Ecomike]

" When I screw it onto the throttle body, the output voltage stays at the low end, and doesn't vary."

When you install the TPS the throttle body lever needs to be pulled back to the other side of the TPS lever as you install it. The way you assembled it the Throttle body lever is not moving the TPS lever.

One of the three wires is the ground.

The three pin connector is for the ECU engine computer, the 4 pin connector is for the TCU automatic transmission computer, if you have automatic. Is your transmission manual or automatic?

 

[cygnus58]

yes it's automatic.
I'm saying the voltage readings differ when the sensor is on/off the engine. This makes no sense to me.
Tried two sensors, same reading.
I'm not considering so much a problem, as the off car ohms all read as per this forum, it's just f'ed that the voltages reading changes when on-board.

 

[Ecomike]

yes it's automatic.
I'm saying the voltage readings differ when the sensor is on/off the engine. This makes no sense to me.
Tried two sensors, same reading.
I'm not considering so much a problem, as the off car ohms all read as per this forum, it's just f'ed that the voltages reading changes when on-board.

You sad earlier below that when the TPS is mounted on the throttle body the TPS voltage did not change from from Idle to WOT, or at least that is the way I read what you said. Is this correct or not? IF it is correct it the Throttle body lever is on the wrong side of the TPS lever as mounted and cannot move the lever as a result. You said and I quote "When I screw it onto the throttle body, the output voltage stays at the low end, and doesn't vary."

Now if you have it installed properly you may have noted that the upper and lower resistance from Idle to WOT is not as high and as low as the unmounted TPS, this is normal. The mounted TPS is limited by the throttle body upper and lower travel limits which is less than the unmounted TPS limits of travel.

 

[cygnus58]

It is mounted right, the throttle moves the lever downward.
The reading doesn't change after it is mounted.
Made no sense to me. The same lead which varied off engine, blue I believe.
I'll have to check it again.

 

[cygnus58]

The erroneous reading I got was because apparantly Renix kills the 5v supply after a few minutes with ignition on and no engine running....

 

[Ecomike]

The erroneous reading I got was because apparantly Renix kills the 5v supply after a few minutes with ignition on and no engine running....

Very interesting, I made the mistake of leaving my engine off, but power on in the run mode for the radio while waiting like 15 minutes in the parking lot. Restarted it and the previously fixed Idle ran up to 2000 rpm and stayed there. Had to go though a shut down/restart procedure 3 times for Renix computer to recover, and fix itself. Never hapened again, never did anything but the shut down restart procedure 3 times. It does not like to left on with out the engine running.