Confirm TPS at fault?

[schlazor]

I have a 1992 2.2L AT that has acceleration issues. No CEL, so I did some normal service stuff to rule that out (new plugs and wires, dizzy cap/rotor, cleaned throttle body). I checked for vacuum leaks but found none. Figured maybe the TPS was at fault so I got my trusty vacuum pump and ohmmeter out and did the diagnostic per the shop manual.

Measuring resistance between VTA and E2 with throttle lever on the stop screw was around 1.6 kΩ. Moved the throttle lever a bit and it dove down to around .5 kΩ, then as I kept moving it it eventually built up again and exceeded 1.6 kΩ and then maxed out around 5 kΩ.

I would think that might be why after the selection of a gear I get really bad acceleration until I'm near the end of the gear and then as soon as the next is selected I get bad acceleration again. From what I understand TPS resistance should be gradual and linear and I've never heard of it dropping and then going back up, but maybe I'm wrong? I did have vacuum applied as per the manual.

Just wanted to check in with others to confirm my suspicion before I buy a new part.

Also, does the TPS on the 5s-fe need to be adjusted in any way? Could it just be out of adjustment?

[fenixus]

I think, if you can catch TPS on dipping down while slowly opening the throttle while ohming it out, this is good enough reason to replace it. new one is around $5 from online dealer.

I have a suspect TPS on my V6, haven't caught it on dipping down yet, but mine starts off 0.6Kohm and maxes out at 3Kohm ... This car also has slight acceleration lag problem.

[Nark]

Originally Posted by schlazor

I have a 1992 2.2L AT that has acceleration issues. No CEL, so I did some normal service stuff to rule that out (new plugs and wires, dizzy cap/rotor, cleaned throttle body). I checked for vacuum leaks but found none. Figured maybe the TPS was at fault so I got my trusty vacuum pump and ohmmeter out and did the diagnostic per the shop manual.

Measuring resistance between VTA and E2 with throttle lever on the stop screw was around 1.6 kΩ. Moved the throttle lever a bit and it dove down to around .5 kΩ, then as I kept moving it it eventually built up again and exceeded 1.6 kΩ and then maxed out around 5 kΩ.

I would think that might be why after the selection of a gear I get really bad acceleration until I'm near the end of the gear and then as soon as the next is selected I get bad acceleration again. From what I understand TPS resistance should be gradual and linear and I've never heard of it dropping and then going back up, but maybe I'm wrong? I did have vacuum applied as per the manual.

Just wanted to check in with others to confirm my suspicion before I buy a new part.

Also, does the TPS on the 5s-fe need to be adjusted in any way? Could it just be out of adjustment?

One would think VTA and E2 would be linear but a closer look that's not true. The resistant between VC and E2 are methodically set so when VTA slide across it can produce a 4 bits signal to fulfill the 4 bit analog-converter inside ECU. I think in your situation the engine just need a good tune up.

[Stillrunning]

Originally Posted by schlazor

Figured maybe the TPS was at fault so I got my trusty vacuum pump and ohmmeter out and did the diagnostic per the shop manual.

Did you use specified feeler gauges? It looks like you didn't do the complete test according to manual? The only adjustment is setting the idle position to get an open circuit (infinity ohms) on IDL and E2.

Measuring resistance between VTA and E2 with throttle lever on the stop screw was around 1.6 kΩ.

That's within spec. 0.2-5.7 kohm

Are you sure you have the OHM meter set to the correct range (multiplier)? Using analog or digital? For this I prefer analog.

[schlazor]

Originally Posted by Nark

One would think VTA and E2 would be linear but a closer look that's not true. The resistant between VC and E2 are methodically set so when VTA slide across it can produce a 4 bits signal to fulfill the 4 bit analog-converter inside ECU. I think in your situation the engine just need a good tune up.

Fair enough - what should I do next, then? Check timing? Would it being out of time not necessarily light up the CEL? New belt was put on about 30k ago.

[schlazor]

Originally Posted by Stillrunning

Did you use specified feeler gauges? It looks like you didn't do the complete test according to manual? The only adjustment is setting the idle position to get an open circuit (infinity ohms) on IDL and E2.



That's within spec. 0.2-5.7 kohm

Are you sure you have the OHM meter set to the correct range (multiplier)? Using analog or digital? For this I prefer analog.

I did the full test with the feeler gauges, and it was all in spec. I watched the resistance throughout the throttle range checking for dead spots since I was under the impression that it's just a fancy potentiometer, but apparently not the case for the 'yotas?

Was using digital. Yes, on the right scale. Checked it a bunch of times just to be sure.

[Stillrunning]

Originally Posted by schlazor

I was under the impression that it's just a fancy potentiometer, but apparently not the case for the 'yotas?

The TPS's that are 3 pin are simple pots but the 4 pin have a micro switch, and that's what you adjust to get infinity ohms (no continuity). I've learned that TPS can check out but when you replace them the problem goes away. You should get a CEL for TPS if the 92 is OBDI and the sensor is not operating properly. They're relatively expensive so you don't want to just re&re for a giggle. Right now I'd look further for another cause of accel issues.

[schlazor]

Originally Posted by Stillrunning

The TPS's that are 3 pin are simple pots but the 4 pin have a micro switch, and that's what you adjust to get infinity ohms (no continuity). I've learned that TPS can check out but when you replace them the problem goes away. You should get a CEL for TPS if the 92 is OBDI and the sensor is not operating properly. They're relatively expensive so you don't want to just re&re for a giggle. Right now I'd look further for another cause of accel issues.

Ah, that explains it then!

Any recommendations on what I should look at next? Timing? Compression test? What could cause my symptoms without throwing a CEL?

[Stillrunning]

Originally Posted by schlazor

Any recommendations on what I should look at next?

You'll have to get more descriptive about the symptoms.

[schlazor]

Originally Posted by Stillrunning

You'll have to get more descriptive about the symptoms.

Sure!

It's an auto, and the symptoms are thus:

Given light to moderate throttle (not enough for kick down), I get very slow acceleration until I'm maybe 2/3 the way through that gear (if that makes any sense). That last 1/3 of the gear is a lot more responsive, but it goes by quick and then it changes to the next gear and I have crappy acceleration again. During the gear change there's a noticeable change from what feels like a responsive drive train to a really hesitant one, almost like I start engine braking. I wouldn't say it's shifting late though, maybe around 4k RPMs. It's the same in every gear. Maybe less noticeable when the car is cold, but it's always there. Like I said, I did a bit of a service just to rule normal stuff out. (air filter, throttle body cleaned out, new spark plugs/wires and distributor cap/rotor, new PCV valve).

Besides testing the TPS yesterday I also did the IAC check where you short the TE1/E1 and bring the RPMs up to 900-1300 for 5 seconds and then lift off - it went back down to normal idle as it's supposed to. I checked voltage on the MAP which was fine but I didn't pull the vacuum hose off and do the other parts of that test as I didn't really feel like taking the glove box off and I was pretty sure it was the TPS.

The CEL does come on during start per normal self test or whatever, so I don't have a burnt out CEL or completely hosed computer. Getting lower 20s MPG, which seems low? Don't know what it's supposed to get, it's always been this way since I've owned it (was a $500 car for me to learn auto repair on).

[fenixus]

^ I have very similar acceleration hesitation here on V6 (started a few months ago) and I performed similar tune up as you did (plus AFR/o2 sensors and ECT sensor and some suspension and brake parts that called for it).

So far I have yet to replace the plug wires and test the ignition coils, but since the car runs almost perfect, I am very inclined to make focus on TPS ...

I don't know how about the 4-pin TPS, but those 3-pin ones (my car has it too) are very simple and I think they actually are supposed to be linear. if yours dips down while opening the throttle then it's the guilty part, no?

they are also inexpensive units, around $45 new OEM.

[Nark]

Ok, I changed out my '86 cressida TPS w/ obd1 today.This is what I got and is very simple. So simple that now I've to change the one on my T100 too Your guys right this is linear and is near perfectly. The first 3 digit 1.xx- ohms is so perfect, the last digit is too fast.

On my cressida it has some skip almost 50 ohms during begining and then it drop below 1k to about 500 ohms and then claw back up to 4.5k at full open. Engine has 225kmi

My T100 is fluctuate around 1k ohm and then kind of freeze around 1.5k and then max at 2.9k at full open. Engine has 150kmi

This is my before symtom: slight hiccups at idle, engine brake at high speed, excessive gas fume despited it has new O2, cat coverter, plugs/wire/cap, temp sensor and poor gas mileage.

With a new TPS, no more gas fume, smooth idle, no more engine brake(almost lost control when exit freeway when test drove) lots smooth transmision shift(I didn't expect that since it's obd1)...the down side...decreased power. I think the engine now run normal so it lost that extra boost from excess gas. Earlier I changed out the spark with Denso TT and I got so much power gained but then back to normal after the new TPS.

Both of these car have one thing in common...exhaust smell.

Will order another one for my T100 tonight. This thing is $70 from rockauto. I don't know why your Camry is cheaper.

Edit: Another thing is I got annoying pings when going up hill on low speed. Now with new tps it cured completely.

[Nark]

Originally Posted by schlazor

Fair enough - what should I do next, then? Check timing? Would it being out of time not necessarily light up the CEL? New belt was put on about 30k ago.

Hey sorry for the wrong info. I feel pretty stupid right about now. If your is fluctuate, yes, I would change it out. I just tested the new one and man this thing is super smooth. The first three digits are inclement exactly from low>high and back down.
Just to clear why I thought the resistor is coded. I got the info from this http://www.autoshop101.com/forms/h16.pdf Now I believed I was interpreting the data given to ECM and not the actual VC-E itself.

[Stillrunning]

Originally Posted by schlazor

I wouldn't say it's shifting late though, maybe around 4k RPMs. It's the same in every gear.

Does it only shift in 4k in all gears, all acceleration modes? 4k seems high unless you're doing some hard accel. What if you work the gears manually, does it still show poor accel? How does it behave if you do slow steady accel? When you punch the gas pedal does it bog or hesitate badly? Does the car shift harshly? You'll need to test the MAP and I would get an analog ohm meter and retest the TPS looking for smooth rise/fall in resistance on slow on/off of gas pedal. Watching the needle is easier than the digital display.

The TPS has limited control over fuel, it signals closed throttle and acts to add fuel quickly when opening throttle quickly. The ECU monitors it's signals and rate of change. The TPS is used mostly for transmission shifting. I'm not saying it's not the TPS, but just to look further to try and eliminate it right now.

[schlazor]

Originally Posted by Stillrunning

Does it only shift in 4k in all gears, all acceleration modes? 4k seems high unless you're doing some hard accel. What if you work the gears manually, does it still show poor accel? How does it behave if you do slow steady accel? When you punch the gas pedal does it bog or hesitate badly? Does the car shift harshly? You'll need to test the MAP and I would get an analog ohm meter and retest the TPS looking for smooth rise/fall in resistance on slow on/off of gas pedal. Watching the needle is easier than the digital display.

The TPS has limited control over fuel, it signals closed throttle and acts to add fuel quickly when opening throttle quickly. The ECU monitors it's signals and rate of change. The TPS is used mostly for transmission shifting. I'm not saying it's not the TPS, but just to look further to try and eliminate it right now.

No, 4k is under moderate but not kick down acceleration. I'll go drive it in a bit to test the rest of those scenarios.

I'll have to go find some different probes for my DMM for the MAP test - mine are way to thick to get in the connectors on the ECU.