SOLVED: Low Idle Stall/Limp mode 5.7 Hemi in a Jeep

[JeepHemi]

Hey folks.

Here is what I have.

2007 Jeep Wrangler Unlimited with a 2010 Ram 1500 5.7 VVT Hemi motor conversion and a Getrag 238 6 spd transmission. It uses a 2010 PCM with a special programming to work with the Wrangler instruments.

This conversion was done professionally about 30k miles ago and has been essentially flawless since then.

Recently once the motor is warmed up and it drops to low idle (it’s a 6 speed so clutch in foot off gas), it predictably will drop suddenly to very low rpm and will often stall. This does not register any CEL or codes and it will start and drive fine afterward.

However in the past week it has gotten markedly worse. Now it will stall anytime the engine hits low idle, and if I “save” it from a stall with some throttle it will start stumbling and go into limp mode. No CEL and no stored codes. It will illuminate the Red “Throttle Control Warning Light” (the red lightning bolt light on the dash).

I’ve checked all the wiring I can get to and all the plugs (accelerator pedal plug and throttle body harness) and they seem solid. Air cleaner is clean, battery is charged, gas is fresh.

I haven’t had time to dig in, but plan to pull the throttle body and clean it if necessary. Other than that I guess I’ll replace parts until it’s fixed (pedal, throttle body, etc).

Any thoughts?

 

[ColdCase]

Check for vacuum leaks, brake booster and/or check valve. Do you still have a TIPM?

 

[JeepHemi]

Check for vacuum leaks, brake booster and/or check valve. Do you still have a TIPM?

Yes it’s still has the original Jeep TIPM.

I’ll pay particular attention to looking at the vacuum lines.

 

[RLJ10X]

There's a real good chance that the guys that did the conversion, know exactly what is going on. The first thing that I'd do, is call them. It's probably something real simple.

I assume you disconnected the battery for 15 minutes.

 

[JeepHemi]

Had a little time to work on the Hemi. Pulled and cleaned the throttle body. Replaced the IAT probe. Checked all the plug connection and wires again. Several battery disconnected resets and still the same issue (and no codes)

Next up a new throttle body and accelerator pedal.

 

[Rampant]

Had a little time to work on the Hemi. Pulled and cleaned the throttle body. Replaced the IAT probe. Checked all the plug connection and wires again. Several battery disconnected resets and still the same issue (and no codes)

Next up a new throttle body and accelerator pedal.

Do you have a decent scan tool that can monitor sensors? Instead of replacing parts blindly, I'd invest in one so you can see what's actually happening. I have an Innova 31603 and it only cost me about $100 on Amazon. It has literally saved me thousands. I have other more expensive ones that are much less capable and less user friendly. There are many many codes that will not throw a CEL but will show (usually as pending) on a good scan tool. Monitoring the TPS percentages would be a great place to start.

Since it seems to exacerbate the fault when you push in the clutch, I'd look real hard near the linkage for any vacuum and electrical binding/rubbing. I'd also pull major harnesses and clean, then put a good coat of dielectric grease on them before reseating. Good luck and let us know what you find!

 

[huntergreen]

My first is the throttle position sensor. Nice jeep btw !

 

[JeepHemi]

Fixed it. The accel pedal assembly was fine, it was the throttle body (which includes the TPS inside). Replaced the throttle body, let it activate (key on - wait 20ish seconds while it initializes the new TB) then started right up. No need for a dealer visit to set up the new TB.

Thanks for the help folks.