Hey Guys,

Just hooked a LapLogger up to my truck and logged a test drive around the block and down the highway.

I reviewed the data and it says that my TPS is at 12.5% even when it is just sitting there idling. It says 12.5% even when the truck is off (not running) and the key is switched on. The TPS should be at 0% when idling, right (no throttle)?

It also says calculated engine load is at 5% (at idle).

The "Butterflys" are definitely closed, and there was nothing holding the pedal or linkage down.

The TPS has been on the truck since before I got it.

Last time I had the battery disconnected was about 2 months ago. It should have "learned" the TPS by now right?

I am thinking the TPS is shot, what do you guys think?

Is this a typical signal for a failing TPS (reading partially open at idle)?

The reason I got the laplogger was to diagnose a miss at idle with no CEL (or intermittently rough idle).

Any input would be appreciated.

My truck is a 2001 Dodge Ram, 5.9L gas, 46RE Auto, 170000 km.

Thanks,
Chris

 

i don't have any experience with a scanner or logger, so i don't know... but, the only way the pcm knows where the throttle is - is by the throttle position sensor. so if the pcm thinks your foot is mashing the gas, then it might not operate the IAC correctly at idle.

for $40-50, i'd just blindly replace it, if nothing else - just to measure it and play with the scanner. (keep you old until proven bad). if you have a buddy with a dodge, hook it up to his truck and compare tps measurements.

 

Mine reads 11 on my Scan Gauge.

 

My factory tps in my Indy read .58v at idle
Doing tps mod (drilling out brass bushings) I could go as high a .72v before tripping a code.
With 5v max output 11-12% sounds about right to me

 

Thanks for the info guys.

Dhvaughan, how does your truck run at idle? Is it pretty smooth?

RM_Indy I thought that the PCM was supposed to read in the base voltage reading of the TPS (around .65V) and then zero the reading at that value when you first turn the key on. So that when the throttle was closed, the TPS would read 0.65V, but the PCM would read that the throttle was 0% open. Is this correct?

Generally I don't like to replace parts unless I can prove that they are bad... but in this case, I might give it a try.

Which sensor is responsible for letting the PCM calculate the load on the engine? Because I was reading 5% load on the engine even at idle.

Thanks,
Chris

 

The engine will always have some load on it. Trans pump, spinning that heavy torque converter, accessory drives, etc. Load is a calculated value, with input from TPS, MAP, and a few other sensors as well.

 

(after a boatload of time and money in tune up's, plenum, timing chain, and sensor) it's very smooth.

at cold idle it jumps to about 1000 rpm and then slowly drops the warm idle to about 600. i've replaced my tps a couple of times whenever the cold idle has surged up and down, or its thrown a P0123 tps code, or acts up in any other way. they seem to be tempermental little bastards. IAC too. i've replaced it 2 or 3 times as well, probably unnecessarily. the problems i've had are always either surging idle, failure to idle/stalling, failure to hold overdrive on cruise, or the feeling of a flat spot/dead spot in the throttle (where you mash the gas a little bit and it ignores you).

 

By how much did your idle surge dvaughan?

I thought I had an intermittent miss at idle, but it looks like it is actually skipping up and down +/- 30 rpm around 625 rpm.

Could this be caused by a TPS?

 

My idle is jumping +/-30 around 700 and the TPS sits about 12% as well.

 

one time my surging cold idle was extreme, bouncing up and down from 1000-1500. 1000 was where it was trying to idle, and then it was kicking up, and back, up and back, up and back... when it warmed a little and the idle rpm dropped down a little, it would quit the surging. new tps fixed it.

another time i washed the engine and got everything nice and wet, and it started surging at warm idle. not a huge jump, but maybe 100-200 rpm. i already had an extra TPS for some reason that i can't remember so i swapped it and it fixed it.

i hate TPS's and IAC's. i keep an extra of each and when they screw up the least little bit i swap one of them out. if it fixes the problem, then i throw the old one away as bad. if it doesn't fix it, i keep the old one and swap the other sensor. its almost always one of the damned two.