4.0 engine low idle

[Top C]

I have low idle after the engine reaches normal operating temperature. This is causing the engine to stall on sudden deceleration. This is has an automatic transmission and its shifting okay.  If I slow/y approach a stop light or sign the engine won't die. It has great pickup no hesitation.  The engine does not have a rough idle its low and does surge very slightly though. I have read through pages here of Idle problems and have follow advice give to others.

 

Here is a check list of what I've done so far.

Cap & rotor replaced

New wires

Plugs replaced

TPS has been checked and set

O2 sensor has been replaced

MAP Sensor has been check

Throttle body was cleaned
Ground wires have been cleaned

C101 connector has been cleaned

All vacuum lines have been checked

CTS has been checked and is working

Vehicle starts up normally and will restart if it dies.

Engine is not burning oil or smoking

Engine does not appear to be running rich

 

Things I have not done

Fuel pressure has not been checked

Injectors have not been replaced

 

Has anyone else had this problem and what did you to solve it. Looking for other ideas that I could check. Also purchasing a Renix reader from Nick which should help also.

 

Thanks for your help in advance.

 

Mike

 

 

 

 

[jeeppapa]

I have low idle after the engine reaches normal operating temperature. This is causing the engine to stall on sudden deceleration. This is has an automatic transmission and its shifting okay. If I slow/y approach a stop light or sign the engine won't die. It has great pickup no hesitation. The engine does not have a rough idle its low and does surge very slightly though. I have read through pages here of Idle problems and have follow advice give to others.

 

Here is a check list of what I've done so far.

Cap & rotor replaced

New wires

Plugs replaced

TPS has been checked and set

O2 sensor has been replaced

MAP Sensor has been check

Throttle body was cleaned

Ground wires have been cleaned

C101 connector has been cleaned

All vacuum lines have been checked

CTS has been checked and is working

Vehicle starts up normally and will restart if it dies.

Engine is not burning oil or smoking

Engine does not appear to be running rich

 

Things I have not done

Fuel pressure has not been checked

Injectors have not been replaced

 

Has anyone else had this problem and what did you to solve it. Looking for other ideas that I could check. Also purchasing a Renix reader from Nick which should help also.

 

Thanks for your help in advance.

 

Mike

You might clean those injectors it wouldn't hurt. Some good videos DIY on line. If you have checked or replace all on that. Cleaning the injectors would just get you down the road that much farther for performance and improved mileage. Not sure if that would fix it but you will be happy you did. After I cleaned the ones on my Eliminator it made a sizable difference. Check your fuel pressure to and change the fuel filter. Totally start fresh with a clean system.

 

 

Sent from my iPhone using Tapatalk

[cruiser54]

If you're gonna do injectors, replace them with Volvo 746 injectors. cheap on ebay. The whole part number is 0 280 155 746. 

 

Are your intake manifold bolts loose? 

[Ωhm]

3 shots in the dark:

1. Transmission converter lockup locked up. (always on)
2. P/N switch tell ECU to kick idle up when shifted in gear. (Does vehicle start in gear?) 
3. Worn out, lazy or tried IAC.

[Top C]

3 shots in the dark:

 

• Transmission converter lockup locked up. (always on)
• P/N switch tell ECU to kick idle up when shifted in gear. (Does vehicle start in gear?) 
• Worn out, lazy or tried IAC.

How do you check for transmission lockup?

No won't start in gear

What is IAC?

[Jeep Driver]

Idle Air Control. 

 

 

That would be my guess too.

[Top C]

Well thanks for all the replies.  I did find a couple things that seemed to improve the idle. I'll know better once I get my engine monitor from Nick.  Here's what I found so far;

 

I had a problem with the NSS - the backup lights were not coming on so I cleaned the switch, it was full of gunk and the two small springs that push on the contacts were gunk up and the one that works the  backup light switch blade was not working at all. I fixed that and now that's working great now. This didn't have any effect on the Idle though.

 

The TPS sensor was replaced just before I purchase the vehicle (which was a Month ago) so the only thing I did was reset it that didn't fix the idle. After exhausting everything else including grounds,  I decided to swap out the TPS sensor with one I had from another 4.0 Renix engine.  I started engine back up and it sound better. I hadn't calibrated it I just put it on and adjusted it to where old one was. This seems to have made a difference as it's not stalling now after its warm up and doing a hard stop or slowing it doesn't seem to stall as it did before.

We'll have to see over time if this fixes the problem with the low idle.  I also forgot to mention I replace the spark wires these were replaced about year ago.  I'd  had heard some arching coming from around the spark area so waited until it was really dark outside and then I started the engine back up and sure enough It was arching around several of the spark plugs wells  I that stop that. Good quality wires can make big difference.

.

 

So we'll see what happens, hopefully this cures the stalling and low idle problem.

 

Mike

 

[cruiser54]

How are you adjusting the tPS?

 

Here's the best way:

 

http://cruiser54.com/?p=54