I'm getting this all the time at Idle. I see it has something to do with the Throttle Position Sensor. 200,000 miles, never touched carb.

Suggestions?

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1986 Black/Gold "GT" Z28
Original Owner, 202K+ near trouble free miles.
Mostly Stock, becoming less stock each day.

1995 Dark Red Metallic Corvette Coupe 36K miles

 

Yeah, your TPS is either bad or maladjusted.
Suggestions. Adjust or replace it
...ed

hehe, seriously, thats what you need to do. First you want to test it now. Get a voltmeter and jumper it into the middle and bottom wire on the 3 wire connector coming from the front ds of the carb. With the throttle closed (make sure the choke isn't on) it should read ~0.5V Yours doesn't, hence the code.
If it reads near 4.5-5V, it is either shot or way out of adjustment. If it reads less then 4V and it increases as you open the throttle it may still be good, just out of adjustment.
Either way, you might as well try to adjust it to see if it's dead. Get a small drill bit and carefully drill a hole in the plug just to the right of the acc. pump arm on the airhorn. Once you have a hole in it, screw a small self tapping style screw into that hole, just enough so that it will grip the plug. Then pull it out with pliers using that screw as a handle.
Now the fun part. You don't even have the tool you need. This is the tool you need. Click Here Once you have that, you can adjust the TPS. If you find that you can't adjust it to get 0.5V with the throttle closed, or that even with it adjusted it doesn't smoothly increase voltage with throttle opening (to somewhere over 4V at WOT) then your TPS is bad.
Replacing the TPS isn't very hard, you just have to take the airhorn off. It's a little tricky, and i definitely suggest having a manual handy in case you mess something up.
Damn i need to turn this into a tech article so i don't have to type it again.

edit...if that damn link doesn't work right, it's at the bottom of http://www.thextontools.com/catalog/fuel/fuel_1.htm , PN 362

[This message has been edited by Ed Maher (edited September 14, 2000).]

 

Sorry to bring up such an old thread, but the shoe fits.

I go to get in the car today and it wont start. After a couple diffrent attemps at starting it fail, I finnaly just crank it over @ WOT for a sec and it fires up and runs fine. The service engine light came on, checked it out when I got home and it ended up being this "TPS code 21" High voltage @ throttle position sensor.

This is a 5.7L TPI car. Before I go about replacing the TPS, just wanted to ask if anyone knew any other things that might be causing this.

Thanks

Josh

 

Uh, this is the "Carburetor" forum, you know. . .

 

I did not know, thank you.
Ill start a new one.

 

Got this code a few days ago. Car ran with a high idle for a while id tap the gas and it would return to normal sometimes, sometimes it wouldnt and id shut the car off and it would diesel out on me. The other day the car began to surge on me at certain point in pedal position and sometimes just would not start at all. could this be pertaining to the problem im having with the tps?

 

Surging at certain pedal positions, maybe.

All the other complaints, ESPECIALLY a no-start, no.

 

surging with light pressure to pedal. when i would give it more throttle(add more pressure to pedal) it engine felt like it was about to shut off. As if it where flooding the carb or fuel pump was failing. I do not have any other codes whatsoever. Air pump diverter sounds busted and I recently plugged a vaccum leak on the water neck. Car has never done this to me. Yesterday the car started fine and ran for about 20 minutes then i came to a red light and while in gear and foot on brake pedal car died out. Pulled air cleaner off poured some gas down the carb cranked and started for a bit before dying. I did this about 3 times before i got her running again and drove her home which is when the dying/bogging started happening.

 

Also just ran the car for about 10 minutes while going on a water run. Sarted up right away and ran, shut off, and started first crank again. So im guessing the problem may be pertaining to the tps after all...? Tps sends signal to computer right? Is my fuel pump mechanic? Would TPS affect fuel flow to carb or in carb at all?

 

Correct. Only thing is, the only thing the computer controls with it, is the mixture (over a range of maybe 16:1 to 12:1), and timing advance.

Can't see what you've got now to be sure, but from the factory, yes.

As mentioned above, only to the extent that the rods are set full lean in the jets (near 100% duty cycle on the solenoid), full rich (near 0% DC), or somewhere in between.

The ECM has relatively little "authority" in a carb system. Not like EFI. It's more of a minor tweeeek than a major "control".

 

inspect your choke and choke pull off.

the choke should be fully closed on a cold start and slowly open over a course of a few minutes once the engine starts running. Should be full open within 5 minutes or so.

the choke pull off should crack the choke blade open slightly as soon as the engine starts up and vacuum is applied to its diaphragm. check it by removing the short section of vacuum hose and pushing the plunger in. hold your finger over the vacuum nipple with the plunger in and the plunger should not move until your finger is removed.

a failing TPS will affect torque converter lock and can cause intermittent converter lock/unlock. this 'may' be the surging you've noticed. sounds like you have more than one problem though.

 

ill check this right now and take photos. it happened to me again yesterday. car died soon after taking off and i had to pour gas in the carb to gt her started again. while driving home she was surging and felt like it was shutting off and starting up and shutting off while i was driving and had the gas pedal depressed, she ran fine today though... i have been getting the choke light come off and on every now and then while driving so....

 

so i just went out and tested the choke pull off. It works. stays pulled in when vacuum is applied however it doesnt seem to do anything to the choke plate and when the green rod thing pulls on the thing connected to the rear choke plate it does absolutely nothing it just goes back and forth freely without opening any plates. front plate seems to always be fully open even before a cold start. also i dont think my secondary choke plate ever opens at all. I ran the car at idle without tps plugged in and had a nice even idle. I plugged the tps back in and the idle went to ****. It was a little rought and kinda surging but not the kind of "car shutting off surging" that im talking about while driving.

 

I also think i broke this a while back while messing with the air filter cover. It is connected to a vacuum which connects in a T connection with the choke pull off before going to the front of the carb. might this be affecting it as well? and if so what is this?

 

The green link thing that goes to the secondaries:

Does nothing whatsoever most of the time. Butt, since the vacuum diaphragm is pulled in under most normal circumstances, when there's high vacuum, it's all the way toward the front almost all the time. BUTTT: when vacuum disappears, such as when the driver floors the gas, a calibrated orifice in the diaphragm allows it to retract rearwards at a controlled rate. Notice that when it's forward, the secondary air valve CANNOT open, i.e. CANNOT let in air, i.e. PREVENTS the carb from leaning out and giving you Quadrabog. It is therefore a control mechanism to prevent that. Quaadrabog is caused almost exclusively by the secondary AV opening when it shouldn't; either too fast when it should be slow, or at too low airflow for the engine to be actually needing it at the moment. Yerbasic lop-eared knuckle-dragger's "improvement" consisting of loosening the AV, only MAGNIFIES it. There's only a handful of us left that know how to tune a Quadrajet... learn from us how it REALLY works and ignore the Friday night In-N-Out parking lot monkey-spank.

The thing in the air cleaner is a temp switch that operates the "Thermac" valve in the snorkel, such that when cold, the valve is closed and the engine gets its air from the heater stove thing around the exh manifold so that it suffers less from general coldness. When it warms up it opens the valve and the engine gets air the normal way. I'd suggest getting a non-broke one at the buzzard nest.

Iunno what part of LA you're in; but when I lived in Carlsbad, I used to use a Pick-and-Pull type place in Oceanside, right off the 78, across from the Oceanside airport. I'd suggest going to there or some similar place and getting one of those "Thermac" switch things out of some car. The same part was in all sorts of cars & trucks so shouldn't be too hard to come up with something that will restore it.