Year+ long issue that no one can figure out with gas pedal

Maintenance/Repairs
1

I’ve had this issue for over a year. I can’t figure it out as I am a car repair noob, and no one else has been able to either. I’ve spoken to some mechanics that have theories. Below are the major points I’ve observed and they are clear and not ambiguous during observation.

  1. The main problem is that when I lightly touch the gas pedal, the car will die. If I press it further, past 10% or so, the car takes off fine and doesn’t die. As long as I have the pedal pressed in past a certain point, it drives fine and cruises just fine. If I come to a stop, then lightly press the pedal again, it will die. Stopping/going is a real issue and tough to deal with stop lights and such. Putting the car in neutral or park will allow the car to idle more normally so it doesn’t die. Putting it in drive again will kill it most of the time unless I immediately gun it.

  2. I don’t hear misfires or anything like that. It doesn’t seem to miss out and sounds smooth in neutral and while cruising.

  3. The problem got to this point over time, and continues to slowly get worse. It used to idle ok in drive, but now will die most of the time while sitting still in drive.

  4. I messed around with the throttle body and replaced the throttle position sensor. This action fixed the problem for 2 months, but then appeared again. I thought it was the sensor that went bad again, but after replacing it with yet another new one, it resolved nothing this time. I assume now that it wasn’t the sensor causing the issue.

  5. The problem is minimized when the car start up fresh, cold. It worsens as the car heats up. There is definitely a correlation with the temperature of the engine it seems.

  6. Autozone used their device for testing the computer and came up with the results in the picture I have attached. The guy said it was ‘running too rich’ according to the device. He suggested it may be vacuum related, purge solenoid, or oxygen sensor related.

This is beyond stressful at this point, especially after starting a new job and wondering if I’ll get to work each day. I will either take it into a place like Firestone and have them test the computer more thoroughly, or I’ll do the trial and error thing if parts are not too expensive. I just don’t know where to start other than the suggestions I got from Autozone and thought I’d come here first to get some expert knowledge. I’m ready to get this solved somehow. Any advice would be much appreciated.

2

Make/model/year/miles/engine/etc?

3

clean idle air control valve yet?

4

Like Texases said need the year, make, model and engine size. Many cars have common problems so knowing what you have helps greatly. Don’t just replace parts randomly, if you want to give money away I will send you a postmarked envelope ;). Getting a accurate diagnosis is a good idea. I am not a big fan of the large chains like Firestone & Pep Boys, fixed too many cars that they threw a ton of parts at guessing. If you can find a good independent tech in your area I would go there first.

From your codes you have 2 issues

P0442 small evap leak: To accurately diagnose this the tech will need a scan tool with the ability to test the evap system. It will also help if he has a smoke machine and the ability to test the gas cap.

P0172 system too rich: Again a tech with a scan tool will be able to read the various sensors and fuel trims while the engine is running to find out what is causing the issue.

Don’t fall into the AutoZone trap of replacing parts listed on their “free diagnosis” sheet. Spending a few dollars on a real diagnosis will have you money ahead in the long run.

Steve

5

Forgot to post why it runs good cold. When a car is first started cold the fuel system is in “open loop” where the the ecm uses default parameters to control the engine. Once the engine is hot the ecm goes into “closed loop” where the ecm relies on multiple sensors to control the engine.

6

This problem cannot be fixed with discusssion. You will need to spend some money on diagnostics. The two codes can be related or may not be, but only running tests will determine that. The P0442 code points to a vacuum leak in the evaporated system. The P0174 points to the engine running rich. The ECM uses vacuum to determine fuel loading, so the leak in the right place can cause both codes. Or maybe you have two separate problems. Both codes are general enough that they do not point to a simple solution.

7

You don’t know what you are doing and you are taking your car to people who don’t know what they are doing. Instead of worrying about whether or not you will get to work, take your car to an actual mechanic, not a parts or tire, or lube shop. If you don’t have a mechanic, get the name of one from the mechanics files here.