Hi everyone! My ride is a 2002 Neon ES that I purchased from a friend.
I'm in need of some help here from those who have scanned theirs' TPS idle voltage.... What voltage do you get at idle? I need to know because the previous owner messed with the throttle stop and also drilled the 1/8 hole on the throttle plate(idle issues). To compensate for the rush of extra air he backed up the screw all the way, but the car(While running great and idling just fine) only gives me 18 MPG Highway. I drive 44 miles roundtrip 7 days a week, so you can imagine the $$ I'm spending just in gas. I'm planning to plug the hole and bring that screw back to the stock position and work any possible issues from there; but I need to know the idle voltage you guys have so I can start in the right direction. The voltage I get with the current set up is .56 at idle and 3.77 at WOT.
Please guys help me with this one so I can stop going to the pump so often due to this TPS being out of range... BTW, I purchased a brand new TPS to replace the old one, just in case.
Thank you for reading! Any suggestion will be greatly appreciated!

 

The PCM supplies approximately 5 volts to the TPS. The TPS output voltage (input signal to the powertrain control module) represents throttle blade position. The TPS output voltage to the PCM varies from approximately 0.6 volt at minimum throttle opening (idle) to a maximum of 4.5 volts at wide open throttle.

 

Thanks for the reply! But is there a specific number for idle, say 0.68V? Or anything above 0.6V is OK for the TPS to send a "good" signal to the ECM?
I just want to make sure, so I can set the throttle stop screw to it's original, or at least an acceptable position that will let me work on finding out what could be the idle problem, and of course, hep with the low mpg issue.

 

The way I read it, 0.6V is what idle should be, up to 4.5V at full throttle.

 

Cool! I'll set it a 0.6 and see how it works. I think I need an AIC valve also. This one only opens a little bit, not letting enough air in to compensate for engine load. It's like the ECM is not sending enough voltage. The car shakes like a washer machine and drops down to 500 rpm under load. Also, the rpms don't drop fast enough when coming to a stop, making the transmission jerk a couple of times before settling down. It kind of stays at 950 for a second or two. I checked for vacuum leaks and can't find one though. Most likely the TPS is bad, though it sends a good progressive signal. Well....

 

Have you filled the hole in the throttle plate? I've got an 1/8" hole in mine, but I don't have a loss of MPG. IAC valves can go bad, but more commonly, get very dirty. You could try cleaning it real good and see what happens.

 

I did. Yesterday. Then adjusted the screw so the TPS will read .60. The car idles fine whith some vibration(motor mounts?) But once I put in in drive it shakes like a ****, making it obvious that there is a problem, and the rpms drop about 100-200. If I turn the A/C on then it dips to 500 RPM while the compressor engages, causing the car to shake even more. Then it ides erratically between 750-650 RPMs. I tested the IAC and even bought another one just in case. Both work Surprisingly on my tests but don't get enough voltage to compensate for load. I've read that it could be the TPS giving the ECM a bad signal, therefore not sending enough voltage to the IAC to open and compensate, but it can also be a bad ECM as I tested the wiring and seems to be fine. Well, what a puzzle. I also have a problem related to the transmission when coming to a stop. the RPMs stay at about 1000 and the car jerks like trying to continue going forward. I don't have any vacuum leaks, so my main suspects are a bad TPS causing the ECM to use too much fuel when decelerating, or a bad MAP sensor, or both. Mmmm. I can be wrong, because the IAC seems to be opening all the way when the car is moving, and then takes a long time to return to idle position keeping the RPMs high and driving the transmission forward... Crazy stuff with these "new cars"... I just replaced the TPS today to see if that fixed the problem, but the car just ran fine for like 5 minutes, then all came back like before. This new TPS reads 0.70 at the position of the old one, and can only adjust the throttle screw enough to get it to 0.68 without stalling the engine. I disconnected the IAC and ran the car like that for a few miles, doing stops and some highway speed and it actually performed better than I thought. What really bothers me is that the car runs fine and pulls strong, but this idle issue kills all the fun.
I just ordered a pre-programmed ECM(VIN#, Mileage, most recent Chrysler flash, lifetime guarantee, etc) from E-Bay. It was on special for $130 so I compulsively went ahead and bought it ... Well, another few days and I'll find out if that's the problem, if not then back to the drawing board. The MAP sensor will be next, after that I don't know what else I can do to fix it.

 

Do a search around the Neon section for more possible diag. information. Idle issues are common with these cars, unfortunately. Drives me up the wall.

 

We have been through this many a time here and I have boiled it down to the motor mount and the fact that it's water filled. There is a sticky just for this issue. Right now the only way I can drive this car is to turn the motor mount bolt out half a turn and it settles down. I have done it all and it still idles rough and i have done everything you have done up above. Still waiting for the solution to this problem ! And BTW I'm pretty sure this is why he sold the car it's very annoying to have the car shake all the time it drives me up the wall and the gas mileage is really bad on my car too i never get more than 20mpg .

 

Yes, the hydraulic filled factory mount not being used when the motor mount replaced is part of the problem. However, there are still known idle issues. Dodge/Chrysler issued TSB's about it.