So my car has slight hesitation from about 20 MPH to 50 MPH. I checked the TPS sensor with my multimeter (positive in the second slot and negative grounded to the battery) and it reads 0.48. I did order a new delco TPS with a gift card I had. I remember reading (or hearing) a few years ago that you can adjust the TPS past 0.54 and get better throttle response off the line. What should I set it too? I just want some stop light fun.

 

The TPS needs to be adjusted to what the computer is expecting. Don't try to fool the computer - if you want tuning then get tuning. Don't mess up the inputs to the ECM.

GD

 

If the TPS is within the range it needs to be, it's not your problem. Adjusting it past it intended parameters won't fix the hesitation either. You need to find out where the root of the problem is. Have you checked fuel system, timing? Could be as simple as bad gas or clogged fuel filter, injector not working properly.

 

Ill just adjust it to .54. I just recall reading either here or on Corvette forums that a lot of guys were adjusting their TPS higher than .54v for drag racing, saying it gave them better response off the line. I've been Googling for the last few days on both forums. Maybe I dreamed it but I could have sworn people were doing that. I know it won't add any more horsepower but I just wanted to add a little more pep off the line for fun.

It can't be bad guys because it's been happening for a while and I've gone through a few tanks. Ignition timing is 6*. I'm leaning towards just the TPS being at .48V and 5+ year old spark plugs. I doubt it's anything in the fuel system, entire fuel system has been replaced save for the injectors but I don't have any symptoms of bad injectors. The idle is fine, gas mile seems normal, no starting issues, no surging, no knock or smoke from the tail pipe, it's not running rich and no gasoline smells from the engine. I've ran a couple of bottles of Techron through the tank too.

 

^^THIS^^


Those guys were full of it.
The TPS is basically, the "accelerator pump shot". It is influential, more from the rate that it's being moved at...rather than whatever it's starting point is. Therefore, changing it's starting point isn't going to do a lot....or anything.

 

Upon start up, the ECM looks at the closed throttle voltage of the TPS and establishes that at 0% TPS.

So yeah, advancing, Advancing it doesn't do anything as itll essentially get zeroed out again. That's a relic from the 80s before people knew how these things work.

 

That came later. It was not part of the MAF programming in 86. You do need to set the voltage for proper operation on the cars with adjustable TPS. On the later throttle body the TPS is not adjustable as the SD cars do set the TPS percentage based on voltage seen as you described.

GD

 

So fuel system is ok, that's one problem area checked off. I still don't feel the TPS will make any difference but try it anyway just to eliminate the possibility. After that I would look into the ignition side. Does it hesitate when cold? Or after a certain amount of time or miles?

 

It only seems to hesitate when cold. I replaced the TPS and set it to .54V and it made a huge improvement. There is still slight hesitation when the car is cold but not as bad. I'm guessing it's just those old plugs at this point.

 

Why would the TPS function differently when the engine is cold? Why would the plugs? There is a LOT of "diaguessing" going on in this thread.

Have you check the CTS?

 

CTS was replaced late last year. The IAC has also been replaced as well as the ECM. All delco units.

 

Well then...guess on!

 

You are loading up the parts cannon and your diagnostic consists of replacing it and then *assuming* that it's good. New parts can be bad right out of the box. It happens. Ever seen a fuel filter that never had the hole punched through the canister (inside the banjo connection in this case) at the factory? I have......

You need to test, verify, and only THEN replace. When you know you are replacing a bad component.

GD

 

Sounds to me like you are in need of a "tune". If you want to stop guessing and throwing parts at the problem download TunerPro RT, get the Moates ALDL connection cable and data log your car. I had the same problem with cold hesitation that got better as the car heated up. The data showed I was running rich, which was causing the hesitation. Your injectors are 30+ yrs. old and may not be firing the same as they did when new even though they show no signs of failure. The Data log will also show all the sensor readings so you will know if they are all functioning properly. I sent the data log to a tuner on this site and he wrote a new chip for the ECM with different fueling and wow it made all the difference in the car.

 

^That. Or grab a scan tool and look at the thing.

 

A sad truth

This applies if you are still having issues after replacing something as well. You should verify it is then operating properly.

 

The thing is though all of those parts were replaced when the car was acting differently. When the ECM was replaced (5 years ago) first my car was running really rich and then it got to the point where it would stall as soon as I stepped the gas. After I replaced the ECM it ran like new.

When the IAC was bad the idle was really rough and sporadic. After I replaced it it smoothed out. That as a while ago.

When the CTS went bad my car would want to stall until it was warmed up. It starts up and idles fine. Just has a slight hesitation when I stomp on the throttle.

 

I ordered a USB ALDL cable. Should be here next week.

 

Throw a new cap n rotor on there with plugs n possibly a coil if it's been awhile just went through that headache this past weekend on my '86 had a miss n a stumble that I thought was just plugs n wires.

 

When you raise the TPS voltage beyond 0.6 you're not actually idling any more. You're cruising, and the computer is going to act like you are cruising.

 

No. The TPS doesn't have that influence. From post #5:

The TPS is basically, the "accelerator pump shot". It is influential, more from the rate that it's being moved at...rather than whatever it's starting point is. Therefore, changing it's starting point isn't going to do a lot....or anything.rate that it's being moved at...rather than whatever it's starting point is. Therefore, changing it's starting point isn't going to do a lot....or anything.

If it did as you say, you wouldn't need a throttle cable...just a TPS cable, to get on down the road.

 

I see. It is always good to make comparisons to how FI works to how a carburetor works.

 

What ever helps people "get it".