Idle Issues - 4.0 - JeepForum.com
 5Likes
  • 1 Post By Skippynutz123
  • 2 Post By MrRoundel
  • 1 Post By MountainMan304
  • 1 Post By MrRoundel
 
LinkBack Thread Tools
post #1 of 15 Old 10-13-2019, 09:08 PM Thread Starter
MountainMan304
Registered User
1997 ZJ 
 
Join Date: Oct 2019
Posts: 8
Idle Issues - 4.0

Evening gents, I'm not new to Jeeps, but never had a "grand" Cherokee. Picked up a purple 97 zj with a 4.0 and it's got idle issues Im hoping someone can help with. I'll try to give as much info as I can. Feel free to tell me I'm spate parts if warranted!

Kid I bought from said it idled like **** when cold, but cleared up eventually. He had IAC valve unhooked already and it fired up, idled like ****, and I drove it 2 hours home with no issues. Figured I would hook IAC back up once and see what would happen. It already had check engine for p0505 and p1899. Kid said a guy had it and was fooling around with wiring harness trying to find a miss or idle issues. Found the wiring on pcm was cut and put back together with those nephson style butt connectors. I know I'm going to have to go through that and solder them correctly, but not sure that's the issue yet. Thing also had a Walmart style "cold air intake". I took that off and put the stock box on with a new paper filter. Still need to run new hoses to it.

I cleared code and now it won't even start without hitting gas. If I give it a little gas it purrs like a kitten. I can see the IAC valve is new, and the Map looked new as well, with an old map sensor in center console. I picked up new iac, cleaned up throttle body a little and installed new IAC. Fired up and it hit high idle just fine, about 1200rom, after about a minute it tried to go to a normal idle and just died. Back to where I started. TPS looks to be unchanged, and def has the wrong bolts holding it in.

I started looking around the thing and found new fuel filter in back floorboard.

My next steps are to install a new TPS, run some new hoses to original stock airbox, and then check wiring if that doesn't bring any results. From my understanding, if it's not the fuel pressure, iac, TPS, wiring issues to iac, it's most likely the pcm?

My initial searches led me to this forum as I found some good related posts. Am I on the right track? Sorry for the long post. Any help is appreciated.


97 zj
4.0 auto
150k miles

MountainMan304 is offline  
Sponsored Links
Advertisement
 
post #2 of 15 Old 10-14-2019, 08:31 AM
jtec
Registered User
 
jtec's Avatar
2014 JK Wrangler 
 
Join Date: Oct 2017
Posts: 6,737
post all codes, this is OBDII so we will be able to seee live data.

The 'modifications' by PO need to be repaired.
The IAC was cleaned and passages were clear?
Do an old school vacuum leak check - a carb cleaner spray..

The CEL and Airbag light should come on @3 seconds EVERY start - yes no?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
jtec is offline  
post #3 of 15 Old 10-14-2019, 11:09 AM Thread Starter
MountainMan304
Registered User
1997 ZJ 
 
Join Date: Oct 2019
Posts: 8
Hello,



The code it consistently pulls is P0505, which relates to the IAC circuit. I sprayed the orifice for IAC clean with TB cleaner.



I posted on a ZJ Facebook group and a guy suggested unplugging battery, turning to start a few times to discharge capacitors, and start it again. Said I would need to give some gas to get started, but to keep it running and let it "learn" to idle.



I did this today with the "old" IAC valve. It wouldn't idle at all, but would stay running with me keepin at about 1000rpm. So, I put the new IAC in that I scored from Advance yesterday. Tried same procedure and now it will sputter along at about 2-300RPM for about a minute then quits. It's an improvement, but something still isn't right.



Here is a youtube video I made of it.



We did spray some carb and TB cleaner around the bay and don't see any mist sucked in. Thanks for your reply, it's very appreciated.
MountainMan304 is offline  
 
post #4 of 15 Old 10-14-2019, 11:12 AM Thread Starter
MountainMan304
Registered User
1997 ZJ 
 
Join Date: Oct 2019
Posts: 8
Forgot to add, the CEL and Airbag light both come on at start and stay on for about 3 seconds. The CEL stays on if the code is tripped.
MountainMan304 is offline  
post #5 of 15 Old 10-14-2019, 02:47 PM Thread Starter
MountainMan304
Registered User
1997 ZJ 
 
Join Date: Oct 2019
Posts: 8
Another update.



Pulled plugs, did compression test, most were 125, with cylinder 1 being about 105.

Cylinder 6 plug gap was about .15, corrected that.

Pulled throttle body, cleaned again, removed basically all the black ****. Put the new IAC back in

Installed new TPS

cleared existing codes, found P0505, P1899, and P0138 this time. First time seeing P0138


pulled battery, hit key a few times, then started.



Started perfect, idled perfect (even miss was gone) for about a minute and then it died again. Kicked the P0505 code again.



Seems like when it's cold I get it to at least start up and run find for a minute.



Shrugs
MountainMan304 is offline  
post #6 of 15 Old 10-17-2019, 08:40 PM
Skippynutz123
Registered User
1997 ZJ 
 
Join Date: May 2018
Location: Anchorage
Posts: 45
Change out your front 02 sensor located under the intake, on the exhaust pipe, I had the same problem with a bad idle, I changed all of the sensors on the throttle body, to no avail, changed the front 02 sensor, and it idled great!
3hounds likes this.
Skippynutz123 is offline  
post #7 of 15 Old 10-18-2019, 09:01 AM
MrRoundel
Registered User
1998 ZJ 
 
Join Date: Jan 2007
Location: California
Posts: 2,425
I agree that the symptoms sound like bad O2 sensor or its associated wiring. It starts in open loop (computer ignores O2 sensor), but when it warms up it goes to closed loop, which will utilize signal from O2 sensor. A vacuum leak is also possible, although many times that will get better as car warms up. Good luck.

BTW: Cleaning the engine grounds is never a bad idea either. If you haven't done so.

1998 Laredo 4.0L 4x4, 242 TC. Turned over 200K miles in 06/18. Original owner.
MrRoundel is offline  
post #8 of 15 Old 10-19-2019, 09:34 AM Thread Starter
MountainMan304
Registered User
1997 ZJ 
 
Join Date: Oct 2019
Posts: 8
So after my last post the Jeep fails to start completely. It's throwing codes p0505, p1899, and p0138. The last one is related to o2 sensor. I have a new pcm and both o2 sensors on the way, along with a rotor button. When we pulled mine it showed some arcing on the end of rotor. Everything else is new. Compression is good, fuel pressure good, getting spark, new plugs and wires and distrib, confirmed distrib was installed correctly.

One thing we noticed when installing new TPS was the bolts supplied with new did not fit. The one currently on it has oversized metric bolts holding it in that clearly are not right. We removed metal inserts from New and installed using old bolts as those are only ones that fit. Wondering if they stripped original out.

I'll update again when I get o2 sensors and pcm. Thanks for replies
MountainMan304 is offline  
post #9 of 15 Old 10-20-2019, 01:35 PM
RedRiverT
Registered User
1997 ZJ 
 
Join Date: Nov 2014
Posts: 603
mountainman, a piece of bad news for you. You said you found a new fuel filter in the back. On a 97, the fuel filter is in a metal can that is mounted to the top of the fuel pump housing ("module"), in the top of the tank. The metal canister contains both the pressure regulator and the pleated paper filter. If there is a separate in-line fuel filter, it was added by one of those hacker previous owners. Unless they poked a hole through the original one, it could still be restricting flow.

But that's beside the point. You want to check the wires to the O2 sensors to see if they are worn through and shorting out. I know you're getting new ones, but you would hate to have a silly little wiring short cause you to chase your tail.
RedRiverT is offline  
post #10 of 15 Old 10-21-2019, 09:38 AM Thread Starter
MountainMan304
Registered User
1997 ZJ 
 
Join Date: Oct 2019
Posts: 8
Hi RedRiverT, I figured out the fuel filter was for something else and was just in the back. I don't see any mods to the fuel line or anything. Fuel pressure is 49-50psi at the rail.

As for the wires, I've been tracing them out and testing them for shorts. So far, I don't see anything bad. The guy cut the main engine harness plug at the PCM and then used those ****ty butt connectors to splice back together. The colors all match up on his repair job, but I noticed two heavier gauged black wires with a gold stripe. To me, these two wires could be reversed easily, so I have to trace them back to their origination.

As far as the o2 sensor go, I've never known of an o2 sensor to cause an no-start condition, which is the point I'm at right now? Won't hit at all.

Thing that blows my mind about all this is I drove this hunk home 2 hours without a single issue. All I did was plug in the IAC valve and my nightmare started.
MountainMan304 is offline  
post #11 of 15 Old 10-21-2019, 10:20 AM
3hounds
Registered User
1997 ZJ 
 
Join Date: Nov 2017
Posts: 77
It SUCKS when you buy a messed with vehicle especially a hacked wiring harness. Unfortunately you're going to go over ALL THE WIRING NOW.


You still might have a bad IAC RIGHT OUT OF THE BOX ?

Last edited by 3hounds; 10-22-2019 at 09:55 AM. Reason: wrong part quoted
3hounds is offline  
post #12 of 15 Old 10-21-2019, 01:48 PM
MrRoundel
Registered User
1998 ZJ 
 
Join Date: Jan 2007
Location: California
Posts: 2,425
I should have mentioned that when you're ordering the O2 sensor(s), you should get the NDK brand. Pretty much anything that communicates with the PCM, BCM, etc., should be Mopar or the OEM type. With the fuel-pump, that's Bosch. With the O2 sensors I believe it is NDK. Always more money but the longevity is much more likely. Even the TPM should probably be a Mopar, although I'm not sure on that one.
Benthal8 and 3hounds like this.

1998 Laredo 4.0L 4x4, 242 TC. Turned over 200K miles in 06/18. Original owner.
MrRoundel is offline  
post #13 of 15 Old 10-22-2019, 10:03 AM
3hounds
Registered User
1997 ZJ 
 
Join Date: Nov 2017
Posts: 77
MrRoundel, It's NGK or NTK not NDK for 02 sensors.
3hounds is offline  
post #14 of 15 Old 10-29-2019, 05:28 PM Thread Starter
MountainMan304
Registered User
1997 ZJ 
 
Join Date: Oct 2019
Posts: 8
Alright boys, I've waited a few days to post so that I could drive the piss out of this thing after the many fixes, and I think I got this some ***** whipped.



I scored some of those butt connectors that have solder in them and seal on the ends with only a heat gun. Worked great, highly recommend. Put a new black plug on the wires going to PCM that the PO rigged. I then installed a new PCM that I ended up getting from Oreillys for about 210 after I take the core back. With new PCM I was able to get the Jeep to actually fire and spit and sputter as it had been doing. The IAC errors were gone, but there were o2 sensor codes like P0132 and P0138. I unplugged the o2 sensors and it fired up and idled pretty nice for running in rich mode. The next day the new o2 sensors came and when I went to put the new one in the cat, i found the whole top of the cat was rusted out, o2 sensor and bung were hanging on by a thread.



I knew I wanted to rip the straight pipe off and had already ordered a cheap Walker muffler from Advance. I found direct fit cats on eBay for about 70-80 bucks, but wouldn't be here for a week. My 2015 Silverado just dropped a torque converter, so I needed these wheels to work. Ate $140 bucks to get a Walker direct fit cat from Advance nearby and was able to install the new o2 sensor and muffler as well.



Purrs like a kitten.



During the o2 sensor change, I decided I'd use a sawzall to cut the tail off the one on downpipe up front. Well, I poked hole in transmission cooler line lol

So, I easily found the 2 that ran up beside the oil pan for about $35 bucks at Advance. I then had to go to AutoZone to get a new connector for the line in rear of tranny (plastic clip was broke).

This is when I found out that you can't get the line that goes from top of radiator to transmission cooler line. So, I bought one for at 97 XJ, as it had the correct ends, and bent the slop into place.



I hope my troubles help someone else down the road.



One thing I did notice was I changed the oil and used some 5w-30 and have some serious piston slap or something now. I guess I'll have to switch to a little heavier weight to quiet it down some.



Thanks for the replies everyone.
3hounds likes this.
MountainMan304 is offline  
post #15 of 15 Old 10-30-2019, 06:47 PM
MrRoundel
Registered User
1998 ZJ 
 
Join Date: Jan 2007
Location: California
Posts: 2,425
Thanks for the "NTK" correction. I knew that but haven't changed one in a while to have refreshed my memory. Cheers.
3hounds likes this.

1998 Laredo 4.0L 4x4, 242 TC. Turned over 200K miles in 06/18. Original owner.
MrRoundel is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.



Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome