Trying to diagnose rough idle on an 89 ta with a fresh 350 swap. Original motor was 305 tpi. I've burned many chips with not much success. Did a search, but didn't come up with the answers I was looking for.

TPS sensor reads normal volts at idle, but won't go up past 1.41 volts when throttle blades are opened. Don't know if this is a bad sensor, mis-adjusted sensor, or normal? Mine goes to over 4.0 volts at wot, just thinking out loud that the 305 sensor or other TPI TPS sensors didn't go to 4 volts, and the pe was scaled down appropriately in the chip? Will probably replace today.

Auto xray scanner reads 242 degrees warmed up, but temp guage reads around 170-180, and car is definitely not overheating. Haven't checked resistance yet, thinking about just replacing cts sensor since it might be old anyway.

I'm thinking the bad reading on the cts sensor is part of the rough idle problem, but just asking for opinions to be sure.

Will probably replace O2, TPS and CTS sensors today to see if they are the problem.

 

The tps is definatly bad. It should go all the way up to around 4.5 v at wide open throttle. The cts could cause the idle problem you suggest and seems to be bad. Condidering how cheap it is you might as well toss it and try a new one.

 

The car is questions is mine...

Replaced the TPS, still the same deal. .54-.58 at idle, and going wide open only gets to 1.27.



I am at a loss w/ that and the CTS. CTS is brand new and went in w/ the new motor.

I am at a loss...

 

unplug the TPS & then turn the key on with the engine off & check the voltage at the connector, if i remember right 2 of the 3 wires should be near 0 volts, 1 is ground which should be no more than 0.03 mv, 1 is signal return which i don't remember about for sure but i think it should be down under 0.5 volts, the third wire should be up around 5 volts. if you don't have 5 volts on 1 of the wires, unplug all of the other sensors, CTS, MAP, air temp & recheck for 5 volts on all 3 wires. if you still don't have 5 volts on any of them check for 5 volts at 1 of the wires to the other sensors. if you don't have 5 volts at the other sensors then check all the powers & grounds at the ecm. if they check good, next start checking for a ground problem on the 5 volt reference wire.
you'll need a wiring diagram & pin out, if you don't have 1 you should be able to find 1 here.

can you pull codes from the ECM? do you have a scanner? if so, can you get data from the ECM?

 

Yup got a scanner and have been pulling codes and readouts from the scanner w/ it not helpoing much. ONly code is a 33 MAF too high code at idle everyonce in a while.

 

The main question is, though, that his car with the old motor went low 15's with that tps sensor, and drove normal, so is it possible that the tps sensor is functioning correctly even though it maxes out at 1.27 volts? Put a new one on last nite and the max it would go to is 1.27 volts wot, and it is slotted.

Anybody else run into a tps sensor that didn't go to 4 volts at wot?

 

Anybody else have any insight?

 

TTT

 

There is no way I've ever heard of that a TPS should only go to 1.27 volts when WOT. One thing though - which wires are you reading it at? Should have your volt meter on the middle wire and the top wire (which are black on the top and blue for the middle on my 91 Firebird TPI setup). I don't do my measurements across the top and bottom wires. You also need to make sure you're getting good contact on those wires. On mine I stripped off a little insulation for 1/4 inch or so 6 inches from the sensore and just insert my probes between the strands on each of the wires. Hope this helps.....


- Vern

 

Using the autoxray scanner for the tps reading.

 

To eliminate another potential problem, try using a volt meter like I suggested and desctribed above. Maybe your scanner or the ECM has a problem......

 

I will try to ohm the TPS wires tomorrow sometime... that and the CTS wires...

Funny thing about it only seeing 1.27 v is that the ECM is still seeing cell 15 when i go WOT w/ the loud pedal.

 

OHM OUT THE WIRES?

NO -- you want to take voltage readings on the wires I mentioned....

Might have just been a slip on words, but just trying to make sure you test it the correct way.

 

test like this. Like the guy says its supposed to go to 4.0 at wot but like his mine only went to like 3.6-3.7

http://www.iroczone.com/techarttpsadj.html

 

Yeah that was a slip... sorry bout that...

Never got around to it... been to busy w/ other stuff... Guess I need to write down a list of todos for tomorrow...

 

anyone know what kind of voltage or ohms i should get testing the wiring for a CTS??

 

With the circuit connected you will get between .5 and 4.5 volts from the cts. The main thing your looking for is a voltage rise as the engine heats up.

 

Thanks guys... I found the culprit tonight...

CORRUPTED ECM...

yeah thats right. I had a feeling since I was having issues w/ the CTS, TPS and O2... that it was more than wiring. I got 89gta383s ECM tonight and put it in... and low and behold the thing ran great... the CTS was correct and working, ranging between 160* and 190*... and the TPS was .52 at idle and 4.37 at WOT...

Thanks again guys...