86 2.5 Running rough/ stalling issue

[eaglescout526]

2 hours ago, jamcomanche said:

My TPS is set right now at around 4.75v at WOT. My understanding is that should cause a high idle, not a low idle. Do you know if that's correct?

A little high but should be fine. 
 

What I like to do in situations like this if I can get the engine to run and stay running, I’d start unplugging things and seeing what changes. 
 

What’s the history on your MJ? I almost wonder if the ISA has been messed with. I also recall having some similar issue where I could get the engine to run right during the time it had a bad headgasket and unplugging the MAP would usually make it run better. I almost think the ISA could be adjusted too low by the PO and now your basically fixing their “fixes”. 

[jamcomanche]

18 hours ago, eaglescout526 said:

What’s the history on your MJ? I almost wonder if the ISA has been messed with. I also recall having some similar issue where I could get the engine to run right during the time it had a bad headgasket and unplugging the MAP would usually make it run better. I almost think the ISA could be adjusted too low by the PO and now your basically fixing their “fixes”. 

Thanks for the response my friend.  Always appreciate being able to reach out to you.  

Thankfully I know it's not that. I've had the truck for about 6 years and I've done a lot of repairs - as well as a lot of correcting things the PO rigged together. The truck has always had it's good days and bad days. Sometimes it would run great and idle smooth. Other times it would idle rough and lack power.  It has never produced a consistent power band and has pretty much always had fluctuations in power during acceleration.

I'm not going to get into the entire list of things I've done to it. but as far as what might be related to my problem: 
I've replaced just about every sensor except for the CPS.
Replaced the fuel pump last year (which was a blast because PO put an XJ sending unit in)
This past weekend I replaced the timing chain, TPS and MAP.

I have not replaced the EGR Valve
I have not replaced the ISA. ( I asked about IAT in my previous post, but I meant to say ISA )
I have not closely inspected the vacuum system or replaced any lines. I've only made sure everything is connected. 
  
As of right now after a lot of searching, I am thinking (and hoping) there is a vacuum leak. There is evidence in my truck that things melt in that area, so I have some 1/8" OD stainless tubing coming in. I'm planning to use that and the existing rubber elbows to replace the small lines at the TB / Intake
 

[eaglescout526]

5 hours ago, jamcomanche said:

Thanks for the response my friend.  Always appreciate being able to reach out to you.  

Thankfully I know it's not that. I've had the truck for about 6 years and I've done a lot of repairs - as well as a lot of correcting things the PO rigged together. The truck has always had it's good days and bad days. Sometimes it would run great and idle smooth. Other times it would idle rough and lack power.  It has never produced a consistent power band and has pretty much always had fluctuations in power during acceleration.

I'm not going to get into the entire list of things I've done to it. but as far as what might be related to my problem: 
I've replaced just about every sensor except for the CPS.
Replaced the fuel pump last year (which was a blast because PO put an XJ sending unit in)
This past weekend I replaced the timing chain, TPS and MAP.

I have not replaced the EGR Valve
I have not replaced the ISA. ( I asked about IAT in my previous post, but I meant to say ISA )
I have not closely inspected the vacuum system or replaced any lines. I've only made sure everything is connected. 
  
As of right now after a lot of searching, I am thinking (and hoping) there is a vacuum leak. There is evidence in my truck that things melt in that area, so I have some 1/8" OD stainless tubing coming in. I'm planning to use that and the existing rubber elbows to replace the small lines at the TB / Intake
 

Of course! Sounds like a weekend of starting out with the easy stuff and going from there.

 

Id start with replacing vac lines just because at this point they’re 40 years old. If yours is an 86, there’s a TSB to replace the rubber block at the base of the TB with just regular vac lines. 

[jamcomanche]

12 hours ago, eaglescout526 said:

Of course! Sounds like a weekend of starting out with the easy stuff and going from there.

 

Id start with replacing vac lines just because at this point they’re 40 years old. If yours is an 86, there’s a TSB to replace the rubber block at the base of the TB with just regular vac lines. 

Thanks.  Mine is an 87.  But I discovered something else today. There are 2 vacuum lines that connect to the intake manifold. one of them is routed to the EGR solenoid over on the passenger side, and if I disconnect that line the engine idles really rough but i can leave the MAP vacuum connected. When I have both connected, it won't run.

I looked at diagrams today and my vacuum system is a mess. The EGR has been connected to a vacuum port on the throttle body cap this whole time, and diagrams show that it's supposed to be connected at the solenoid. The one on the cap is supposed to run to the air box. 

 

SMH... 

[eaglescout526]

30 minutes ago, jamcomanche said:

Thanks.  Mine is an 87.  But I discovered something else today. There are 2 vacuum lines that connect to the intake manifold. one of them is routed to the EGR solenoid over on the passenger side, and if I disconnect that line the engine idles really rough but i can leave the MAP vacuum connected. When I have both connected, it won't run.

I looked at diagrams today and my vacuum system is a mess. The EGR has been connected to a vacuum port on the throttle body cap this whole time, and diagrams show that it's supposed to be connected at the solenoid. The one on the cap is supposed to run to the air box. 

 

SMH... 

 

Sounds like a fun weekend date with the vac lines haha. I think I have a pic somewhere of my MJ of how the lines are supposed to be. Luckily 87-90 remained the same. But sounds like the EGR is essentially being opened and causing your issue. Which yeah actually if you open the EGR on a setup that runs fine, it’ll bog down and or die.