Possibly a bad TPS and low LTFT? '97 GP GT

Hi guys,

First of all I hope you're all OK and would like to thank all of you for all the previous help!

1 - The other day I took a look at the scanner and noticed the LTFT would read from +3 to -22.4 (at different moments) while idling. I know the PCM is taking fuel from the cylinders.

My first thought was a bad MAF sensor (even when the PCM doesn't needs it during open loop operation), which I replaced one or two years ago along with a new MAP sensor. I went ahead and disconnected the MAF to see if it would fix the problem but it didn't and the LTFT would constantly range from +15 to -15 at all times. I guess the MAF should be OK, correct?

My second thought was a leaky injector which would cause the sputtering as well so I used the fuel gauge tester I have to check fuel pressure and any bleeding after turning off the engine. I thought I had found the problem when I saw the fuel pressure was a bit high so I went ahead and replaced the fuel filter, checked feed and return lines, checked FPR too and everything was OK. Later I found out a piece of rubber on one of the EVAP lines was cracked and causing a vacuum leak. I fixed it and pressure went back to within spec but didn't fix the problem.

Third thing was to replace the air filter. It was dirty but even after replacing it, problem was still not fixed...

The upstream O2 sensor switches between rich and lean quickly, I don't think it's gone lazy. I can't remember the exact readings but I could take a look at them tomorrow, I think it ranges between .800 to .250 volts more or less.

2 - Lately, the car has been sputtering for a second ONLY during the first startup everyday. If I step on the gas to lift the revs it will even out and will work OK for the rest of the day. After a few hours of driving the engine will feel like it has lost some power and will be slow to respond; sometimes I have to floor it just to overtake another car; even at WOT it feels slow.

My first thought was a bad/dirty IAC (on the sputtering) so I removed it, cleaned both the pintle and shaft, and reinstalled; didn't work.

I kept searching the internet and found out the TPS might be the culprit too. I connected my cheap live data capable scanner to take a look at the TPS value but since it has a slow refresh rate and no graph, I can't be sure if it's OK. The sensor does ranges from 0 to 100.

Second test was to backprobe it, and test for resistance with a DMM. Same story, the DMM has a slow response and even when the results showed no weird spikes I can't be sure about it. I would get a better one but my uncle will undergo for surgery next week and I cannot afford other expenses at the moment.

This morning, I decided to disconnect the TPS and start the car. It started so smooth and didn't sputter. I took it for a test drive and the car felt great, no lack of power.

Would that last test surely point to a bad TPS, or it's only forcing the PCM to stay in open loop and masking another problem?


Can a bad TPS also affect the fuel trims?


Am I missing anything else about these two problems?

3 - I can feel a moderate cycling vibration with the A/C ON so I took it in to the A/C shop to have inspected. The guy said the compressor was fine but was a bit low on refrigerant so he drained the old one and refilled with new refrigerant and oil.

I can feel the vibration in the cabin and specially on the brake pedal. Seems to vibrate/resonate more (for a second) sometimes when going over speed bumps. I took a look at the compressor pulley and clutch and it's OK.


My question here (and since I feel the car shudder at 1500 RPM's during acceleration about which I posted previously) is if a bad engine or transmission mount can cause both vibrations?


I'm sorry for the long post, I really wanted to cover as much as my knowledge allows me to.

Thanks in advance, I will appreciate any comments!

Oscar.

Oscar, if I were you, I'd start by cleaning the throttle plate, and the IAC valve and passage. What are your IAC counts when you first start in the morning? Also check them while cruising at a steady speed and report back.

PS LTFT bouncing all over the place is not uncommon as long as you dont have an SES light. But the sputtering when first starting is not norma.

After a cold soak (overnight), it wouldn't hurt to check the intake air temp and then coolant temp values to see how they compare. Make sure they are within a few degrees of eachother and a few degrees within the actual ambient temp.

Otherwise it sounds like you are on the right track.

Thanks Tim, it's good to hear from you! Hope you're OK.

Even when the IAC and passage are clean, I'll end up removing the entire throttle body to give it a better clean.

Unfortunately my cheap scanner can't read IAC counts, It will only read generic data. About the IAT and ECT you're correct; if I remember correctly the IAT was about 2 ºC from the ambient temp, and ECT was about 3 degrees form the IAT. Based on your info, they should be alright.

Do you have any idea on number 3?

Thanks,

Oscar.