Novak Conversions Jeep Wrangler TJ engine mounts

RPMs up and down while coming to a stop and sometimes at a stop

boganst

New Member
Original poster
Joined
Sep 11, 2024
Messages
18
Location
Colorado
2001 TJ 2.5

I've gone through the boards and tried a few things. Cleaned the IAC and throttle body. Tested it with a new TPM and IAC plunger. Reset the PCM. Replaced all my air intake hoses (some were missing, rerouted, plugged when I bought it) and have looked for leaks but have not done a smoke test.

The problem is random so I can't repeat it at will. When I am driving if I release the gas the RPMs hold where they are for a second then slowly starts to drop. Seems normal. However, when I depress the clutch that seems to be when the RPMs will shoot up 500-1000. Then they will drop while I coast with the clutch in. Then without changing anything the RPMs will shoot back up and then down. Kinda like a pulse. Once I get to a stop that's when everything seems to go back to normal but not all the time. Sometimes the RPMs will shoot back up while stopped both with the clutch in and out while in neutral. Sometimes I slow down and stop and everything is normal.

The worse part is sometimes while stopped and I just released or release the clutch and give the car some gas, that will cause the RPMs to shoot up to 2000... sometimes even 3000 and hover there for 3-4 seconds before coming back down. This is more rare than the regular RPM isue and sometimes during those times I have the small evap leak and large evap leak codes thrown. I replaced the gas cap but this still happens. Clear the codes and CEL stays off until the next spike in RPM

It's weird because sometimes the Jeep drives fine without any RPM issues. Other times I feel like the guy next to me thinks I want to race.

I'm in the process of replacing the cold air intake setup the PI put in with a stock air handler. Kiinda not sure what to do next but before I take it to a mechanic figured I would give this forum a shot. Below (I hope) is a video of the RPM.

 
Do the smoke test to find / rule out vacuum leaks. Also consider a failing throttle position sensor.
 
So I had it running on the driveway and just started to manually give it gas from the throttle body. It was doing its erratic RPM thing. Then I just started putting pressure on the part that connects the throttle cable to the body and the RPMs shot up. I put pressure in all directions and even pushed it the opposite way than giving it gas, and the RPMs went up. I disconnected the TPS sensor plug and the problem went away. I could do whatever I want and it behaved normally. It threw TPS codes but seemed to run fine. Reconnected the TPS and the problem returned. Bad TPS? Do I just have to replace it to see if that is it?
 
Air leaks around the throttle body shaft are common. You may have one. As I said above do the smoke test to find your possible vacuum leaks and repair them. Until you fix your leaks throwing parts at it, such as a new throttle position sensor, is pointless.
 
IMG20240619101436_01.jpg
 
I ended up replacing the fuel pump and making sure the wire harness was secure. That seems to have fixed this problem. I still get a little RPM rise and fall as it warms up or coming to a stop. Once I come to a complete stop the RPM drops and holds at idle.
 
  • Like
Reactions: macleanflood
Novak Conversions Jeep Wrangler TJ engine mounts